I've been browsing through these forums, and there seems to be a lot of bad advice being given out to those of us that are looking at moving up into 3" exhaust systems (myself included). I thought it appropriate to do a write up on the issue of back pressure. I'm new to magna's, but not new to go-go-mobiles.

The definition of back pressure is:

Restrictions in the exhaust system that slow the exit of exhaust gases from the combustion chamber.

To quote another post of mine, back pressure can be caused by small tubing, bends, badly flowing mufflers etc. Backpressure will be present in any system, but the less backpressure there is, the better. There is no "required amount of back pressure" to be had in any system.

Therefore you won't lose any power in a 3" system. In stupidly large exhausts, you can lose the effectiveness of the scavenging effect (the effect in which gasses are forced out of the system), and therefore lose a small amount of bottom end power. But it must be noted this loss is not created as a result of "low back pressure".

The perfect system is where the fastest velocity is achieved with the least restriction possible.

Exhaust gases moving out of your exhaust can be used to pull other exhaust gases out of your cylinders. Thats why extractors are made the way they are. This effect is called scavenging. The faster the gases move, the more you benefit from scavenging. Moving gas creates a vacum behind itself.

The larger the exhaust, the slower the gases move, so less scavenging occurs. (this is not to say a large volume of gas isnt being moved; it most likely is, but at a slower speed)

The smaller the exhaust, the faster the flow. (this does not mean a high volume of gas is being moved. Because it is restricted, the gas that is moving is moving faster through the available space).

So the trade off is velocity against volume, to some extent. That being said, just because your exhaust gas is moving hyper fast through that drinking straw, that doesnt mean a lot of exhaust gas is being moved. We want move that exhaust gas moderately quickly through something that won't cause any restriction. Restriction is our enemy.

And back pressure is restriction. Therefore, very little back pressure (I would say none, but on any car that has an exhaust, there will always be a shmidget, even on the best system money can buy. You could always take your exhaust off... if you dont love your ear drums and the gift of hearing) is good back pressure.

So next time you hear someone warn someone against getting that 3" system because of 'loss of back pressure', slap them.

Hard.

Sources:
http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm
http://www.club240.com/forums/showthread.php?s=&threadid=1406
http://www.ford-trucks.com/forums/archive/index.php/t-80881-backpressure%20required.%20fact%20or%20myth%20%3F% 3F%3F%20(Falcon%20you%20there%3F%3F)
http://www.miata.net/garage/KnowYourCar/S4_Back.html
http://autorepair.about.com/library/glossary/bldef-044.htm

would this apply to smaller cars?
one of my mates owns a 92 pulsar with a 2" pipe installed. he didn't go any bigger because he said "i'll loose back pressure".... can i smack him?...HARD!! :bowrofl:

If you'd like to read up a bit more on back pressure and exhausts in general, check out:

http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm

http://www.club240.com/forums/showthread.php?s=&threadid=1406

Bigger is not always better, but it sure kicks the **** outa smaller. :bowrofl:

Nicely put Old chap :clap:

I use the analagy that its like a syphon, to thin a tube and you dont get much flow, too large and you lose suction, like baby bear it has to be just right.

Papa bear said someones been sleeping in my bed
And momma bear said someones been sleeping in my bed
and baby bear said, well.........g'night everyone. :bowrofl:

would this apply to smaller cars?
one of my mates owns a 92 pulsar with a 2" pipe installed. he didn't go any bigger because he said "i'll loose back pressure".... can i smack him?...HARD!! :bowrofl:

Slap him, but only for thinking of putting a big ass exhaust on such a small car. I'd say he'd lose the effectiveness of any scavenging effect. Biggers not always better. It'd sound like a little fart machine though. :bowrofl:

Slap him, but only for thinking of putting a big ass exhaust on such a small car. I'd say he'd lose the effectiveness of any scavenging effect. Biggers not always better. It'd sound like a little fart machine though. :bowrofl:

yeah its one heck of a rice box. he told he made calculations before he went out and got the exhaust....... i just laughed and said "are you an engineer???" He works at target fulltime lol i wanna know what hes learning

Your writings very much reflect a web page i found...

what you said:

The perfect system is where the fastest velocity is achieved with the least restriction possible.

What they said

The optimum is where the fastest velocity is achieved with the least constriction possible.

Did you get your text from web pages? if so, please provide your sources.

I've been browsing through these forums, and there seems to be a lot of bad advice being given out to those of us that are looking at moving up into 3" exhaust systems (myself included). I thought it appropriate to do a write up on the issue of back pressure. I'm new to magna's, but not new to go-go-mobiles.

The definition of back pressure is:

Restrictions in the exhaust system that slow the exit of exhaust gases from the combustion chamber.

To quote another post of mine, back pressure can be caused by small tubing, bends, badly flowing mufflers etc. Backpressure will be present in any system, but the less backpressure there is, the better. There is no "required amount of back pressure" to be had in any system.

Therefore you won't lose any power in a 3" system. In stupidly large exhausts, you can lose the effectiveness of the scavenging effect (the effect in which gasses are forced out of the system), and therefore lose a small amount of bottom end power. But it must be noted this loss is not created as a result of "low back pressure".

The perfect system is where the fastest velocity is achieved with the least restriction possible.

Exhaust gases moving out of your exhaust can be used to pull other exhaust gases out of your cylinders. Thats why extractors are made the way they are. This effect is called scavenging. The faster the gases move, the more you benefit from scavenging. Moving gas creates a vacum behind itself.

The larger the exhaust, the slower the gases move, so less scavenging occurs. (this is not to say a large volume of gas isnt being moved; it most likely is, but at a slower speed)

The smaller the exhaust, the faster the flow. (this does not mean a high volume of gas is being moved. Because it is restricted, the gas that is moving is moving faster through the available space).

So the trade off is velocity against volume, to some extent. That being said, just because your exhaust gas is moving hyper fast through that drinking straw, that doesnt mean a lot of exhaust gas is being moved. We want move that exhaust gas moderately quickly through something that won't cause any restriction. Restriction is our enemy.

And back pressure is restriction. Therefore, very little back pressure (I would say none, but on any car that has an exhaust, there will always be a shmidget, even on the best system money can buy. You could always take your exhaust off... if you dont love your ear drums and the gift of hearing) is good back pressure.

So next time you hear someone warn someone against getting that 3" system because of 'loss of back pressure', slap them.

Hard.you work at an exhaust shop?

you work at an exhaust shop?

I've worked in a few places mate.

But if you have any doubts, don't take my word for it.
http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm

I've worked in a few places mate.

But if you have any doubts, don't take my word for it.
http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htmi asked if you worked at an exhaust shop. i take your word that u found a site that fed you this crap but have you worked in the field

Ive been trying to tell these guys this info for years now. What would I know hey :gtfo:

i asked if you worked at an exhaust shop. i take your word that u found a site that fed you this crap but have you worked in the field

Haha, I thought you might have a go at me for this, reading some of your other posts. No I haven't mate, I'm not an exhaust specialist. By the sounds of it you are? I'm just regurgitating what I've discussed with a few blokes at my local shop, a bloke who deals RPW products, and of course the forementioned websites.

And Hyper TF, I've updated my original post. Most material taken from http://www.nsxprime.com/FAQ/Miscell...hausttheory.htm . If you need more let me know.

Thanks for that... anyway, moving on.

TC, i never doubted what you have said about it in the past, though I have been told 2 theories for and against now by 'experts' so sometimes you just don't know what to believe.

You should know who to believe by now madmag :P

let me put it to you guys like this since everyone thinks the net holds the keys to all the uknown questions in life.
if you go into an exhaust shop and you have an exhaust leak does it lose power? off course because the carbon monoxide is flowing freely through an opening and causing the car to run lumpy. why? because the engine hasnt got enough time to componsate the loss of CM02 for C02 (thats fresh air for exhaust air for all of you who arn't in the know. This same principal works for ehaust diameter. if you have an exhaust piping that is too big for your cars engine to handle/componsate its going to lose "POTENTIAL" power (note the word Potential within speach marks). you still gain power in some case's. but in most case's especially in cars with smaller capacity engines that are otherwise naturally aspirated like your magna, this doesnt do any justice.
Now alot of you may have notice me poping up in almost every exhaust related thread. Why because I have and still do work with the exhaust industry. I have and still do see many ppl fall for the Myth "Bigger Is Better!". I've even witness a Magna owner who demanded he be fitted with a "SICK 3" system" and was warned that he was wasting money but did it any way and you know what he regrets it. he tells me theres more power but my verada is quicker. Hmmmm.............. i have a 2.5 " system. Magnas aren't Skyline GT-R's. they're not WRX's. Nor Are they 200sx's. These cars are all turbos. Magnas however are not. Why can a Turbo car have a 3" system you ask? because of the Words FORCED INDUCTION. A turbo can quite easyly componsate for any loss of air flow that is lost through excess exhaust tubing. Whereas like I've previously stated a standard N/a small engined car cannot. In my reccomandations and those of countless exhaust shops 2.5" is plenty for a Magna. you don't need more you can always have less. its up to you if you wanna get ROOted by those who want nothing but to sell you the most expensive exausht they can **** feed you go for it. don't say no one warned you. but if you wanna save muney that doesnt need to be spent and get the most form your exhaust take my advice.

TC, i never doubted what you have said about it in the past, though I have been told 2 theories for and against now by 'experts' so sometimes you just don't know what to believe.

I completely agree. The only reason I've chosen this 'theory', however, is because after reading lots and lots of bull**** about how exhausts work, this theory seems to make the most sense.

I think I understand why people are confused about back pressure though. I think people associate back pressure with high velocity exhausts, due to the constriction caused smaller piping, when really back pressure is the term applied to restriction, ie, like that caused by the ****ty triflow magna muffler. :bowrofl:

I completely agree. The only reason I've chosen this 'theory', however, is because after reading lots and lots of bull**** about how exhausts work, this theory seems to make the most sense.

I think I understand why people are confused about back pressure though. I think people associate back pressure with high velocity exhausts, due to the constriction caused smaller piping, when really back pressure is the term applied to restriction, ie, like that caused by the ****ty triflow magna muffler. :bowrofl:
Do you even know what your talking bout dude? High Velocity Exhaust? go to a proper exhaust shop and ask them about exhaust sizes for your magna not a performance shop where all they do is head work and **** but a shop that SPECIALISES in Exhaust because seriously dude your going down the rong path of advice.

because the engine hasnt got enough time to componsate the loss of CM02 for C02 (thats fresh air for exhaust air for all of you who arn't in the know. This same principal works for ehaust diameter. if you have an exhaust piping that is too big for your cars engine to handle/componsate its going to lose "POTENTIAL" power (note the word Potential within speach marks).
What the hell is CM02? Or C02 for that matter (That's C-zero-two you've written). I assume you mean carbon dioxide (CO2) but why is the engine compensating for a loss of it? Why does the engine care? After all, it's the catalytic converter that changes the carbon monoxide into carbon dioxide.

let me put it to you guys like this since everyone thinks the net holds the keys to all the uknown questions in life.
if you go into an exhaust shop and you have an exhaust leak does it lose power? off course because the carbon monoxide is flowing freely through an opening and causing the car to run lumpy. why? because the engine hasnt got enough time to componsate the loss of CM02 for C02 (thats fresh air for exhaust air for all of you who arn't in the know. This same principal works for ehaust diameter. if you have an exhaust piping that is too big for your cars engine to handle/componsate its going to lose "POTENTIAL" power (note the word Potential within speach marks). you still gain power in some case's. but in most case's especially in cars with smaller capacity engines that are otherwise naturally aspirated like your magna, this doesnt do any justice.
Now alot of you may have notice me poping up in almost every exhaust related thread. Why because I have and still do work with the exhaust industry. I have and still do see many ppl fall for the Myth "Bigger Is Better!". I've even witness a Magna owner who demanded he be fitted with a "SICK 3" system" and was warned that he was wasting money but did it any way and you know what he regrets it. he tells me theres more power but my verada is quicker. Hmmmm.............. i have a 2.5 " system. Magnas aren't Skyline GT-R's. they're not WRX's. Nor Are they 200sx's. These cars are all turbos. Magnas however are not. Why can a Turbo car have a 3" system you ask? because of the Words FORCED INDUCTION. A turbo can quite easyly componsate for any loss of air flow that is lost through excess exhaust tubing. Whereas like I've previously stated a standard N/a small engined car cannot. In my reccomandations and those of countless exhaust shops 2.5" is plenty for a Magna. you don't need more you can always have less. its up to you if you wanna get ROOted by those who want nothing but to sell you the most expensive exausht they can **** feed you go for it. don't say no one warned you. but if you wanna save muney that doesnt need to be spent and get the most form your exhaust take my advice.

I did point out that bigger is not always better. The main point of my argument was, however, that the trade off is velocity versus volume. For example, the amount of gas you move through a system as compared to the speed at which you move it. Now while a 2.5" system may be close to the perfect size, I do not see why a 3" system will be worse. More volume.

Now you say that "you can always go smaller", I believe that to be incorrect. You'll increase your gas velocity with a smaller pipe, but that doesnt mean you'll be increasing the amount of gas your moving. For example, take a drinking straw and blow through it. The air feels like its coming out at the end pretty quickly, but in reality the volume of air moving is relatively slow. Then take a cardboard toilet roll, and blow in it. You'll run out of breath quicker, but you wont feel anything at the end of the pipe.

I'm not saying you should whack a 5" exhaust on your car, you'll have close to no scavenging effect. You might as well take the whoel bloody thing off. But I see close to no evidence that says a 3" exhaust is not going to perform as well as, if not better than a 2.5" exhaust on a 3.5L V6.

Cmon, guys let's talk technical for a minute.

I recall from memory that this is how my Redback cat back exhaust is designed (excuse the crude paint diagram lol)... it was labelled "Z-Flow" as the gasses don't exit through a straight path; instead hopping from one pipe to another through the rear muffler... the amusing thing I was told this was the case to promote some degree of back pressure if this is not the case, can someone please explain the point for this z-flow concept by a trusted exhaust manufacturer.

I am not saying the theory is true or false... I was told and shown why this was the case.

Do you even know what your talking bout dude? High Velocity Exhaust?

High velocity means 'going really fast'. As in, gases moving really quickly out of an exhaust. That is, after all, what our exhaust systems are supposed to do? Move gases quickly and efficiently?

What the hell is CM02? Or C02 for that matter (That's C-zero-two you've written). I assume you mean carbon dioxide (CO2) but why is the engine compensating for a loss of it? Why does the engine care? After all, it's the catalytic converter that changes the carbon monoxide into carbon dioxide.
it still is Carbon Monoxide wen it leaves the back off the system. the engine doesnt think it acts it hasnt got a brain therefre it doesnt care. it composates because if the car does not have C02 it cannot run.
It will always have C02 so long as theres access to it though it can have not enough of it if it is forced to run too quickly it cannot componsate with the standard fuel system and intake system. this is where FORCED in duction takes place. what im trying to get at is air assists fuel that is bburnt in the combustion chamber which produces Carbon monoxide which exits through the exhaust ports into the exhaust system now if your system is too big the air will escape too quickly not giving the engine enough tyme to restart the cycle and you could face a lumpier drive and you will almost definatly experience a flat spot.

I was told this was the case to promote some degree of back pressure if this is not the case, can someone please explain the point for this z-flow concept by a trusted exhaust manufacturer.
My guess, as is my opinion of all mufflers, it was one possible trade-off between flow and muffling ability (i.e. SPL).

My guess, as is my opinion of all mufflers, it was one possible trade-off between flow and muffling ability (i.e. SPL).
ok yeah, that makes sense. I have read something about a mirror something or other, where basically they try to design mufflers so sound waves travelling down the exhaust path, are crash into each other at one point to try to cancel waves out as much as possible to dull the noise emitted down... it makes sense.

Makes me wonder how loud the redback system could be :badgrin:

Cmon, guys let's talk technical for a minute.

I recall from memory that this is how my Redback cat back exhaust is designed (excuse the crude paint diagram lol)... it was labelled "Z-Flow" as the gasses don't exit through a straight path; instead hopping from one pipe to another through the rear muffler... the amusing thing I was told this was the case to promote some degree of back pressure if this is not the case, can someone please explain the point for this z-flow concept by a trusted exhaust manufacturer.

I am not saying the theory is true or false... I was told and shown why this was the case.
that is a good subject to bring up the design of that uffler is called BAFFLED goes in through one and zigzags to the other end the exhaust fumes are slowed to form back pressure. it gives a nice sound its usually refered to as a semi-sports or just a sports muffler depending on the design etc. a straight through is to still alow the air to flow quickly but at the same time the piping is purfirated in a way that the air is still caught in the muffler for a lil while that is BAck Pressure. you didnt get fooled you got a decent muffler.

take a cardboard toilet roll, and blow in it. You'll run out of breath quicker, but you wont feel anything at the end of the pipe. youv'e asered your own question you run out of breath. what do you think the engine does?

it still is Carbon Monoxide wen it leaves the back off the system. the engine doesnt think it acts it hasnt got a brain therefre it doesnt care. it composates because if the car does not have C02 it cannot run.
It will always have C02 so long as theres access to it though it can have not enough of it if it is forced to run too quickly it cannot componsate with the standard fuel system and intake system. this is where FORCED in duction takes place. what im trying to get at is air assists fuel that is bburnt in the combustion chamber which produces Carbon monoxide which exits through the exhaust ports into the exhaust system now if your system is too big the air will escape too quickly not giving the engine enough tyme to restart the cycle and you could face a lumpier drive and you will almost definatly experience a flat spot. Ok it sounds like you're fundamentally talking about the same thing FROGi is talking about - a larger diameter exhaust reduces the scavenging effect.

Other than that I'm confused. An engine will always see CO2 because there's a non-trivial quantity of it in our atmosphere, but other than that, I'm not sure what part it is supposed to play.

If your exhaust is too big, the combustion by-products won't exit the exhaust very fast at all. The smaller the exhaust diameter, the greater the gas velocity, and the greater the scavenging effect, not the other way around.

To get the most power from an engine, you want to get rid of the spent charge as quickly and completely as possible, you don't want to leave it behind. That's one of the reasons why forced induction is so good, you always have a positive pressure on your inlet side. This is also why high-performance N/A cams have more overlap than hi-po turbo cams.

edit: fixed logic error

My guess, as is my opinion of all mufflers, it was one possible trade-off between flow and muffling ability (i.e. SPL).

Yeah, thats my udnerstanding. Mufflers are always going to be restrictive, thats their job, and for the best peformance no muffler would be the way to go, but of course if we were allowed to drive around like that we'd all have to give up the gift of hearing.


air assists fuel that is bburnt in the combustion chamber which produces Carbon monoxide which exits through the exhaust ports into the exhaust system now if your system is too big the air will escape too quickly not giving the engine enough tyme to restart the cycle and you could face a lumpier drive and you will almost definatly experience a flat spot

But wouldnt you be talking something ridiculously large for an effect like that? If a 2.5" system creates an excellent scavaging effect, then how much different can a 3" system be? I'd assume it'd be something very similar, especially at higher rpms.

what do you think the engine does?

Runs out of breath? Nah, that sounds a little absurd to me.

You should know who to believe by now madmag :P
Be careful of excessive cranial inflation there lol

I might believe you on many things but with the rest, i think you're full of **** :bowrofl: :P

Hang on, after reading that again I'm completely confused.


it composates because if the car does not have C02 it cannot run.
It will always have C02 so long as theres access to it though it can have not enough of it if it is forced to run too quickly it cannot componsate with the standard fuel system and intake system

And this relates, how? CO2 to run? I thought CO2 was the biproduct of the engine, after a cylinder fires? And it's what we pump out the ass end of our cars?

Yeah, thats my udnerstanding. Mufflers are always going to be restrictive, thats their job, and for the best peformance no muffler would be the way to go, but of course if we were allowed to drive around like that we'd all have to give up the gift of hearing.



I understand that, and without knowing any better I'll say that makes a lot of sense. But wouldnt you be talking something ridiculously large for an effect like that? If a 2.5" system creates an excellent scavaging effect, then how much different can a 3" system be? I'd assume it'd be something very similar, especially at higher rpms.
3"= too much loss of air as my BOss told me "you always need to have eir in the exhaust its the way it works" im not saying smaller is bbetter but im also not saying bigger is better im saying that you should match your car with the best size that it will run with. a 2.5" system will run smoothly and not lett too much air escape. a car with forced induction will strgle a lil with a 2.5 " system where as a 3" system will be ideal. the air can flow faster and better and there will be no starvastion of oxygen to the motor. your motor does breath. its called an airfilter. if the airfilter throttlebody and intake Plenum cannot suck in enough air your motor wiill starve/choke and turn off.

Hang on, after reading that again I'm completely confused.



And this relates, how? CO2 to run? I thought CO2 was the biproduct of the engine, after a cylinder fires? And it's what we pump out the ass end of our cars?
carbon dioxide is wat you breath in true? carbon monoxide is not what you want to breath in that is why it is known as a form of suicide to breath in the gasses emitted from the exhaust.

3"= too much loss of air as my BOss told me "you always need to have eir in the exhaust its the way it works" im not saying smaller is bbetter but im also not saying bigger is better im saying that you should match your car with the best size that it will run with. a 2.5" system will run smoothly and not lett too much air escape. a car with forced induction will strgle a lil with a 2.5 " system where as a 3" system will be ideal. the air can flow faster and better and there will be no starvastion of oxygen to the motor. your motor does breath. its called an airfilter. if the airfilter throttlebody and intake Plenum cannot suck in enough air your motor wiill starve/choke and turn off.

Loss of air? Through an exhaust?

Now I'm completely confused. Letting air escape? Aren't we trying to f*** the air off out of the exhaust anyway?

Starvation of oxygen to the engine because you have a large exhaust? Just how does that work? Just because you've got a big ass, doesnt mean your mouth gets any smaller.

Sorry, but how the f*** will your motor "starve/choke and turn off" just because your running a 3" system?

FRE5H, you probably design good exhausts, but I'm not convinced you understand why they work.
Don't get me wrong, there's no problem with that. After all, it's the end result that counts.

carbon dioxide is wat you breath in true? carbon monoxide is not what you want to breath in that is why it is known as a form of suicide to breath in the gasses emitted from the exhaust.
Oxygen is what you breathe, dude. It's what the engine breathes too.

Sorry, but how the f*** will your motor "starve/choke and turn off" just because your running a 3" system?
He was referring to induction of air... not exhaust

I think people need to slow down a bit as I doubt you are really reading what is being said properly and misunderstanding is going on... just slow down a tad lol

Edit: especially for us older ones ha ha

ok i know jack about exaust
what would be the best system for a
second gen 3L V6 and 4 banger
and for the 3.5L third gen?

carbon dioxide is wat you breath in true? carbon monoxide is not what you want to breath in that is why it is known as a form of suicide to breath in the gasses emitted from the exhaust.

Do you know what a cat converter does?


it composates because if the car does not have C02 it cannot run.
It will always have C02 so long as theres access to it though it can have not enough of it if it is forced to run too quickly it cannot componsate with the standard fuel system and intake system.

Now explain how this works? Sorry if I'm slow on the uptake, but I dont understand your argument at all.

edit: Post made more friendly. :D

Now explain how this works? Sorry if I'm slow on the uptake, but I think you're talking ****.
I don't know if you have noticed but I am trying to calm this thread down and keep the tone lighter, but keep this up and it will close pretty soon. That is not just to you either.

Thanks

Loss of air? Through an exhaust?

Now I'm completely confused. Letting air escape? Aren't we trying to f*** the air off out of the exhaust anyway?

Starvation of oxygen to the engine because you have a large exhaust? Just how does that work? Just because you've got a big ass, doesnt mean your mouth gets any smaller.

Sorry, but how the f*** will your motor "starve/choke and turn off" just because your running a 3" system?
it wont turn off ok listen here. firstly you need to learn about how a car operates. air goes in air goes out your air filter does notsuck in enough air to feed an engine that is lettin out too much exhaust air . your engine will run faster if there is a consistant flow of the engines "breathing cycle" this is hard to explain over text but **** here it goes,
now wen the exhaust fumes have escaped the combution chamber more air is needed to repeat the cycle but if the exhaust is escaped to quikly the engine needs to force itself to suck in more air quickly. though in most cases it cannot on a standard engine. which is why alot of manufacturers use a EGR Pipe (exhaust gas REturn Pipe.) to "Help" the engine burn faster by reusing a fraction of the exhaust fumes.

He was referring to induction of air... not exhaust

I understand that, but just how exactly does the amount of CO2 breath relate to having a 3" system? Unless he's feeding his exhaust back around into his intake?

:bowrofl:

I don't know if you have noticed but I am trying to calm this thread down and keep the tone lighter, but keep this up and it will close pretty soon. That is not just to you either.

Thanks

Sorry mate, I was trying to keep it toned down, I realise my last post came out as otherwise though. This is a good discussion, we might finally get to the bottom of all the rumours circulating around about exhausts. It's only a forum after all.

Do you know what a cat converter does?



Now explain how this works? Sorry if I'm slow on the uptake, but I think you're talking ****.
a cat reduces the emmisions of "Bad Air" i.e Carbon monoxide. however there is always traces to be found in the end result of the exhaust cycle. the honey comb inside a catalitic converter has a chemical reaction to that of the carbon monoxide and elemenates a percentage of the gas to that of carbon DIOXIDE. but as ive said there is still traces of it in the end result

it wont turn off ok listen here. firstly you need to learn about how a car operates. air goes in air goes out your air filter does notsuck in enough air to feed an engine that is lettin out too much exhaust air . your engine will run faster if there is a consistant flow of the engines "breathing cycle" this is hard to explain over text but **** here it goes,
now wen the exhaust fumes have escaped the combution chamber more air is needed to repeat the cycle but if the exhaust is escaped to quikly the engine needs to force itself to suck in more air quickly. though in most cases it cannot on a standard engine. which is why alot of manufacturers use a EGR Pipe (exhaust gas REturn Pipe.) to "Help" the engine burn faster by reusing a fraction of the exhaust fumes.
You have that all wrong.

EGR exists as an emissions control device. It slows down combustion rate and lowers the combustion temperature to lower the production of oxides of nitrogen. It achieves this because the exhaust air doesn't contain much oxygen and hence isn't a very good combustion catalyst.

The number one main aim in exhaust design is to get all the spent air out and replace it with clean, burnable, air. This is why people spend hundreds of dollars on extractors and ported heads. You don't end up with a more efficient engine by leaving exhaust gas in the cylinders.

You have that all wrong.

EGR exists as an emissions control device. It slows down combustion rate and lowers the combustion temperature to lower the production of oxides of nitrogen. It achieves this because the exhaust air doesn't contain much oxygen and hence isn't a very good combustion catalyst.

The number one main aim in exhaust design is to get all the spent air out and replace it with clean, burnable, air. This is why people spend hundreds of dollars on extractors and ported heads. You don't end up with a more efficient engine by leaving exhaust gas in the cylinders.
i know that is true that is why they are almost always the first thing to go on a exhaust upgrade, they arent the most effective design for a performance application but they are good sorce of emission control good point

it wont turn off ok listen here. firstly you need to learn about how a car operates. air goes in air goes out your air filter does notsuck in enough air to feed an engine that is lettin out too much exhaust air . your engine will run faster if there is a consistant flow of the engines "breathing cycle" this is hard to explain over text but **** here it goes,
now wen the exhaust fumes have escaped the combution chamber more air is needed to repeat the cycle but if the exhaust is escaped to quikly the engine needs to force itself to suck in more air quickly. though in most cases it cannot on a standard engine. which is why alot of manufacturers use a EGR Pipe (exhaust gas REturn Pipe.) to "Help" the engine burn faster by reusing a fraction of the exhaust fumes.

So the exhaust puts out "more exhaust air", as you say, because it runs a larger exhaust? That doesnt make sense to me, the same amount of gas should be exiting through a larger area by rights? How does the larger space area at the end of the exhaust create a larger vacum effect, making the engine "force itself to take more air in", as you've been saying? The scavaging effect is not as strong in a larger exhaust correct? The gases would be hanging around longer if anything, as we go back to the "small pipe iz fast, large pipe iz slow" theory.

If what your saying is true, then why do extractors work so well?

Sorry mate, but I still dont accept any of that.

ok yeah, that makes sense. I have read something about a mirror something or other, where basically they try to design mufflers so sound waves travelling down the exhaust path, are crash into each other at one point to try to cancel waves out as much as possible to dull the noise emitted down... it makes sense.

Makes me wonder how loud the redback system could be :badgrin:
I'm gonna try not get into this discussion much, but HyperTF what you are mentioning here where the waves crash into each other is not just for noise, as its not only sound waves but pressure waves, and with back pressure, it creates more waves going back "up" the exhaust, and when these crash with the normal flow of the exhaust it creates a vaccum which in turn helps with scavenging, hence why back pressure is needed, it also depends on extractor/header design, and many other variables, exhaust ports etc. which is why some cars respond well to reduced backpressure, and others don't
I'm not saying anyone is wrong, with the whole backpressure theory, i'm just giving my side of what i was taught at TAFE (for my mechanics trade).
But even the TAFE's have been wrong before, i'm just showing another theory about backpressure.

and with back pressure, it creates more waves going back "up" the exhaust, and when these crash with the normal flow of the exhaust it creates a vaccum which in turn helps with scavenging
That's an interesting spin - using "back pressure" (deliberate restrictions) to tune pressure waves. Good call.

I expect it would be a fairly high precision thing to do and would be very car specific.

I'm gonna try not get into this discussion much, but HyperTF what you are mentioning here where the waves crash into each other is not just for noise, as its not only sound waves but pressure waves, and with back pressure, it creates more waves going back "up" the exhaust, and when these crash with the normal flow of the exhaust it creates a vaccum which in turn helps with scavenging, hence why back pressure is needed, it also depends on extractor/header design, and many other variables, exhaust ports etc. which is why some cars respond well to reduced backpressure, and others don't
I'm not saying anyone is wrong, with the whole backpressure theory, i'm just giving my side of what i was taught at TAFE (for my mechanics trade).
But even the TAFE's have been wrong before, i'm just showing another theory about backpressure.


I agree with you mate, i did my Thesis on this topic, i can post my document if you like, i did my thesis on the intake side, but same law applies on the exhaust side.

I'm gonna try not get into this discussion much...
Now that makes sense too thanks...

oh and I just looked it up... it was not mirroring, it was "reflection" I meant lol :nuts:

I expect it would be a fairly high precision thing to do and would be very car specific.
Well they said my type of muffler/exhaust was designed for the Magna! They have a pretty wide range.

That's an interesting spin - using "back pressure" (deliberate restrictions) to tune pressure waves. Good call.

I expect it would be a fairly high precision thing to do and would be very car specific.

Yeah, thats sounding pretty high tech! So restriction can be used for good as well? Or is it the bends that do the work? Do you know anywhere I can read up a bit more on this theory? Sounds cool.

So the exhaust puts out "more exhaust air", as you say, because it runs a larger exhaust? That doesnt make sense to me, the same amount of gas should be exiting through a larger area by rights? How does the larger space area at the end of the exhaust create a larger vacum effect, making the engine "force itself to take more air in", as you've been saying? The scavaging effect is not as strong in a larger exhaust correct? The gases would be hanging around longer if anything, as we go back to the "small pipe iz fast, large pipe iz slow" theory.

If what your saying is true, then why do extractors work so well?

Sorry mate, but I still dont accept any of that.
ahh extractors are know as collectors elsewhere meaning they collect the exhaust fumes and bring them together evenly the size/length of the extractors add to the effect. on a 4 cylinder engine for example you want the pipes to be equal or close to equal in length to provide the bbest airflow to the system. after that the sytem takes charge,

Also to go with my previous post, the vaccum is also because of the tailpipe,as it is the opening to atmospheric pressure, which is why an exhaust leak affects performance, because it changes the flow between each wave crashing into each other, buy having another opening to atmospheric, thats why exhaust systems are best designed as a whole, as the flow,waves etc obviously all starts from one end then ends at the other.
Its hard to explain withou being right in front of you, but i hope you get what i mean.

I thought the length of the extractor pipes were at such precise but differing lengths to promote a pulse by pulse flow away from the engine after the combustion cycle so the amount of bottle necking is reduced.

Yeah, thats sounding pretty high tech! So restriction can be used for good as well? Or is it the bends that do the work? Do you know anywhere I can read up a bit more on this theory? Sounds cool.
this is what ive been trying to tell you and you are unlikely to get this effect with a 3" sstem.

I agree with you mate, i did my Thesis on this topic, i can post my document if you like, i did my thesis on the intake side, but same law applies on the exhaust side.
if you could it would be great, i'm not the best at explaining things

I thought the length of the extractor pipes were at such precise but differing lengths to promote a pulse by pulse flow away from the engine after the combustion cycle so the amount of bottle necking is reduced.
yes and know depends on the application and the car etc. but usually the case is the pipes should be even to allow an even amount of flow adawise you mite end up with a lumpy untuned engine as you have sum exshaust fumes flowing quicker from one cylinder than another

yes and know depends on the application and the car etc. but usually the case is the pipes should be even to allow an even amount of flow adawise you mite end up with a lumpy untuned engine as you have sum exshaust fumes flowing quicker from one cylinder than another
The only way you could really have them at equal lengths is to have seperate exhausts per cylinder as they all have to meet up in one place?

this is what ive been trying to tell you and you are unlikely to get this effect with a 3" sstem.

Nah, reading back through your posts... I dont mean to be picking on you mate, not at all, but these guys are bringing a completely new perspective to it all, whereas I still cant quite grasp what you were trying to explain to me before, it seems to be quite unrelated. Might just be that your style of writing and I are incompatible.

RPW seems to think otherwise as well, in regards to the 3" system. Not saying they're the gods of all things exhaust and magna, but they wouldn't push a 3" system for N/A cars if it was going to adversely affect peoples cars? Or would they...

:bowrofl:

I agree with you mate, i did my Thesis on this topic, i can post my document if you like, i did my thesis on the intake side, but same law applies on the exhaust side.
It's a bit different though, right? Correct me if I'm wrong, but on the intake side you're talking about tuning runner length, yeah? When the inlet valves close the air in the runner collides with the valve and rebounds off of it. The idea being that by the time the inlet valve opens again, the wave front has bounced off the back of the plenum and has arrived back at the valve just in time to be ingested into the engine.

In the exhaust we're talking about riding the low pressure zone at the back of the wave to draw air out of the cylinders.

The only way you could really have them at equal lengths is to have seperate exhausts per cylinder as they all have to meet up in one place?
thats right a seperate pipe per cylinder froming into one hence your 3into1 pipes and so forth.

DUUDES lol


E-MAIL THE MYTHBUSTERS! :cool: :bowrofl:

DUUDES lol


E-MAIL THE MYTHBUSTERS! :cool: :bowrofl:

Hahaha, best idea I've heard all day. Here's a quote from the RPW website...


RPW has found that upgrading the whole system to a complete 3" system ie 3" cat converter, resonator, muffler and piping mandrel bent whilst does not on a fairly stock motor increase horsepower over the above 2 1/2" system, nor did it lose horsepower or torque. We have found the vehicle to be non - responsive in this size meaning that either sizing works well. The 2 1/2" system tends to be slightly quieter. But if you are planning on doing more work later being camshafts, twin throttle bodies, internal engine work etc then the 3" system is definitly the way to go to bring it in line with future mods. And since there is no loss of power over a 2 1/2" system its the perfect way to go.

So you won't get 'extra' power out of a 3" system, but your not going to be losing any either. I can see why the 2.5" system is recommended so highly, does the job fine by the sounds of it. By the sounds of it though, for those of us who want an almighty roar, 3" is the right way to go?

thats right a seperate pipe per cylinder froming into one hence your 3into1 pipes and so forth.
no no, not quite what I meant... I know that's how it is he he... now hold on, what did I mean lol

I thought you were saying that the pipes from the block to the join would have to be equal in length, which I didn't think they were stock, whereas the headers are designed to compensate for the mis-lengthened stock pipes...

oh i am trying to work here and think about this at the same time... lol

Hahaha, best idea I've heard all day. Here's a quote from the RPW website...



So you won't get 'extra' power out of a 3" system, but your not going to be losing any either. I can see why the 2.5" system is recommended so highly, does the job fine by the sounds of it. By the sounds of it though, for those of us who want an almighty roar, 3" is the right way to go?
w8 now you making a different statement you want power or just sound?? and even then you can get a decent sound outof a 2.5" system hence my signiture

So you won't get 'extra' power out of a 3" system, but your not going to be losing any either. I can see why the 2.5" system is recommended so highly, does the job fine by the sounds of it. By the sounds of it though, for those of us who want an almighty roar, 3" is the right way to go?
3" is for people who want an almighty drone ;) 3" is loud, especially combined with the engine mods I've got.

3" is for people who want an almighty drone ;) 3" is loud, especially combined with the engine mods I've got.
yes 3" is loud on a magna with the right mods but hey like ive said my cars louder and its 2.5" so hmmmmm your also forgeting that for a deep sound you want the sound waves to b able to "bounce" of something so you mite want a smaller system than a 3" i remember i bodged up my olde vns exhaust by cutiing out the back too mufflers and just replacing the rear the result was a 100db car. loud enough at the tyme ive since wantd louder

w8 now you making a different statement you want power or just sound?? and even then you can get a decent sound outof a 2.5" system hence my signiture

No I'm not making a different statement, but you were saying all these nasty things aobut 3" systems before. Such as what you were discussing earlier, in regards to the engine "choking itself" with a 3" system, and the loss of back pressure being evil. Where RPW doesnt mention this at all?


3"= too much loss of air as my BOss told me "you always need to have eir in the exhaust its the way it works" im not saying smaller is bbetter but im also not saying bigger is better im saying that you should match your car with the best size that it will run with. a 2.5" system will run smoothly and not lett too much air escape. a car with forced induction will strgle a lil with a 2.5 " system where as a 3" system will be ideal. the air can flow faster and better and there will be no starvastion of oxygen to the motor. your motor does breath. its called an airfilter. if the airfilter throttlebody and intake Plenum cannot suck in enough air your motor wiill starve/choke and turn off.

no no, not quite what I meant... I know that's how it is he he... now hold on, what did I mean lol

I thought you were saying that the pipes from the block to the join would have to be equal in length, which I didn't think they were stock, whereas the headers are designed to compensate for the mis-lengthened stock pipes...

oh i am trying to work here and think about this at the same time... lol
uve lost me :S
:S

No I'm not making a different statement, but you were saying all these nasty things aobut 3" systems before. Such as what you were discussing earlier, in regards to the engine "choking itself" with a 3" system, and the loss of back pressure being evil. Where RPW doesnt mention this at all?
y do u think they dont? they just wanna sell you the most expensive thing they can

your also forgeting that for a deep sound you want the sound waves to b able to "bounce" of something so you mite want a smaller system than a 3"
I'm not forgetting that at all :P

Believe me, my exhaust is quite deep, it burbles nicely, and sounds great on the overrun.

But it does drone a bit under load at around 2100-2500rpm. Haven't got a plan to 'fix' it yet, but it's on the cards.

how do you upload sound files i wanna show you wat my cxar sounds like

y do u think they dont? they just wanna sell you the most expensive thing they can

Hahaha, probably very true!

But to the original argument of "the back pressure myth"... I dont think we've really gotten anywhere. Obviously there's far less back pressure in a 3" system, yet it still remains effective, albeit without any gains in power over a 2.5" system.

Now this what I thought I had figured out in the beginning of the thread. That restriction isn't neccesary at all. This is what most texts I've read tend to suggest.

how do you upload sound files i wanna show you wat my cxar sounds like
You can't. Feel free to email me, and I'll host it on a web site for you if you don't have anywhere else to host it.

uve lost me :S
:S
We are saying the same thing, I might not have said it right in the first place...

I doubted the stock pipes were equal lengths and the point of the headers is to correct it, that is all lol

Obviously there's far less back pressure in a 3" system, yet it still remains effective, albeit without any gains in power over a 2.5" system. That needs to be clarified a bit..

"Obviously there's far less back pressure in a 3" system, yet it still remains effective, albeit without any gains in power over a 2.5" system on their particular test car".

I wonder if that would hold true through a car, such as mine, with some mild engine work.

Edit: for the record, I think my 3" system is too big. I kind of ended up with it by accident ;)

That needs to be clarified a bit..

"Obviously there's far less back pressure in a 3" system, yet it still remains effective, albeit without any gains in power over a 2.5" system on their particular test car".

I wonder if that would hold true through a car, such as mine, with some mild engine work.

Edit: for the record, I think my 3" system is too big. I kind of ended up with it by accident ;)

Good point. Is there anyone else out there running the big 3? I suppose since you can't really trust the RPW sales shpeel, the only way of really knowing is by having two identical Magna's, with the two different alternatives on each?

The reason I'm so interested, is because up until recently I was sold on the RPW philosophy that I could rule the world with a 3" system, and after reading a few websites, and talking to RPW, it seemed to make sense.

Hmm, and at the start of this discussion I thought the whole thing was so straightforward...

:bowrofl:

Please excuse me, I just wanted to jump in and comment on HyperTF's remarks about the Redback muffler being a "Z design" - then I'll get out of the way and let y'all get back to the important topic of arguing over 2.5 > 3 (who really gives a ****?? :nuts: )

Neil, when I unwrapped my new redback muffler a few months back - I was surprised to find that the 'intake' piping was on the oposite side of the muffler to the 'outlet' side.

I felt rather ripped off as I had been led to believe up til this point that the redback muffler was a straight thru design. It wasn't til a couple of days later, when I was actually fitting the muffler that I happened to look straight up the 'outlet' end of the pipe - and to my surprise, instead of seeing the pipe continue in a 'straight' line into the muffler and then terminate (as in your diagram) I saw the pipe make a rather sharp bend - towards the oposite side of the muffler.

It is my opinion after seeing this that the redback muffler is infact straight thru, but the design is in such a way that it is as close to the stock muffler as possible (hence all std hangers are able to be used, and piping exits in exact location as std muffler tips). I'm not saying the person who told you it was a Z design was purposely deciving you - just that they formed an opinion of the muffler based on the external apperience of it (as did I when I first saw it)

Here's my version of what I think the Redback muffler design resembles........ but aside from cutting one open it's almost imposible to prove or disprove:

Please excuse me, I just wanted to jump in and comment on HyperTF's remarks about the Redback muffler being a "Z design" - then I'll get out of the way and let y'all get back to the important topic of arguing over 2.5 > 3 (who really gives a ****?? :nuts: )

Sorry if it seems a little mindless, but I'm more interested in the science behind it all, rather than just the 2.5" versus 3" argument. If there's a solid reason why ones better then the other (as I thought I knew at the start of this thread), I wanna know! The only argument I've heard against the 3" system is that of back pressure, and I challenged that theory at the start of this thread. And of course the argument that RPW says its awesome, therefore it is. Now I'm not so sure... :doubt:

Here's my version of what I think the Redback muffler design resembles........ but aside from cutting one open it's almost imposible to prove or disprove:
Sorry to upset you further but that design was stuck in my mind from the Redback product design manual they showed me with more or less the same diagram...(albeit glossy and colourful) unless they have changed the design my picture is the G.O.

Sorry dude... you can cry on my shoulder now :cry:

Sorry to upset you further but that design was stuck in my mind from the Redback product design manual they showed me with more or less the same diagram...(albeit glossy and colourful) unless they have changed the design my picture is the G.O.

Sorry dude... you can cry on my shoulder now :cry:
redback actually design a str8 thru muffler like the one BLACK BEARD showed ive fitted one to a GEN3 sound pretty awsome

redback actually design a str8 thru muffler like the one BLACK BEARD showed ive fitted one to a GEN3 sound pretty awsome
Oh well, then they have different versions... I am still impressed with the note, suits a V6 nicely IMO.

Oh well, then they have different versions... I am still impressed with the note, suits a V6 nicely IMO.yeh i think yours was designed for sound rather than power but still gives a healthy boost in power so u did good. for wat u were after

yeh i think yours was designed for sound rather than power but still gives a healthy boost in power so u did good. for wat u were after
Oh noes lol all i keep reading lately says you don't really gain much at all if anything powerwise from a sports exhaust... You may only gain something if you had the pipes venting seperately straight from the block

I think i have been confused enough for one night... i better go home before I do my head in lol... play nice.

Oh noes lol all i keep reading lately says you don't really gain much at all if anything powerwise from a sports exhaust... You may only gain something if you had the pipes venting seperately straight from the block

I think i have been confused enough for one night... i better go home before I do my head in lol... play nice.
hehe exhaust can make you naucious.

It's a bit different though, right? Correct me if I'm wrong, but on the intake side you're talking about tuning runner length, yeah? When the inlet valves close the air in the runner collides with the valve and rebounds off of it. The idea being that by the time the inlet valve opens again, the wave front has bounced off the back of the plenum and has arrived back at the valve just in time to be ingested into the engine.

In the exhaust we're talking about riding the low pressure zone at the back of the wave to draw air out of the cylinders.


you are correct, i wanted to say that when we experimented with the lenght of the exhaust, ie extractors, he power curve shifted accordingly, simmilar to the way it does if you install longer inlet runners.

should of have been a bit more clear

no no, not quite what I meant... I know that's how it is he he... now hold on, what did I mean lol

I thought you were saying that the pipes from the block to the join would have to be equal in length, which I didn't think they were stock, whereas the headers are designed to compensate for the mis-lengthened stock pipes...

oh i am trying to work here and think about this at the same time... lol
The primary pipes in a perfect world would be equal length. The crank determines the firing order of the pistons and the pipes need to be aligned to have even spacing of exhaust gas pulses to provide a balanced and effective scavenging.

The 4cyl motors are dead easy, just mate all 4 primaries into the one collector and the engine timing will provide the rest. You could also (more expensive to make, so less common) run say cylinders 1 & 3 into a collector/secondary pipe and 2 &4 into a secondary pipe. These secondaries then merge into another collector and become the main exhaust.

V8s are more complicated (forget V10s and V12s!!), there aren't even spaces between cylinder fires on each bank of the motor. Hmmm :think: Header manufacturers generally shrug and just make a set of headers for each bank. The correct method would be to have cross-over pipes under the sump so that an even cylinder firing space is achieved and hence the exhuast pulses are balanced per header bank and scavenging is maximised.

V6s: We CAN have a bank specific header due to our 1-2-3-4-5-6 firing order. 1-3-5 and 2-4-6 sets.The firing pulses are identical between each consecutive cylinder firing in these 2 sets. To ensure we maximise this nicity, EQUAL LENGTH PRIMARY PIPES MUST BE USED.

Think of an exhaust pulse as a soccer ball flying thru a pipe. If the gap delay between each pulse/ball is constant, they will never actually collide. As revs increase, the gap becomes smaller. If the primaries were of unequal length, the pulses or balls would collide and lose their potential energy for creating a vacuum behind them. The mismatch of pipe lengths and the rpm that the pulses collide will hurt performance at that rpm band and above. Unfortunately who know were that might be. Too bad if its at 2000rpm!

One day I'll talk about primary pipe length and how it effects power delivery. Think of the velocity of a bullet from a pistol vs from a rifle.

The diameter of the pipe should really be calculated to move the highest volume of exhaust gas at the highest possible velocity at the desired operating rpm. Now, let the physicists do some work.

there is such thing as having too larger exhaust for the capacity of the car, this is fact. I dont know the technical reasons for this, but i remember reading in a street commodores mag (i think it was street commodores??) a while back they did a number of exhaust tests. They ran a twin 2.5" exhaust system on a VR V8 SS, they ran no mufflers or cats on the car so to eliminate as many variables as possible and dyno'd the car. They then changed the pipes to twin 3" pipes and dyno'd the car, oh and they tuned the ECU to suite the two different systems so to eliminate any thoughts that the factory ECU tune favoured one setup over the other. If this theory of "the larger the better" was correct then the twin 3" should have produced more power, however it didnt! The twin 2.5" system produced an average of something like 10 or so more HP at the wheels.

There is obviously a size of exhaust that is too small, but there is equally a size that is too big. The trick is to find the balance. Look at V8 supercars for example, they could run twin 6" exhausts if they wanted to, but they dont! Why? cos its too big even for a fire breathing V8 supercar engine (i think they run twin 3" or 3.5" not sure.. probably varies from team to team too)

you are correct, i wanted to say that when we experimented with the lenght of the exhaust, ie extractors, the power curve shifted accordingly, simmilar to the way it does if you install longer inlet runners.

should of have been a bit more clear
That sounds like fun. Was it possible to construct a mathematical model for this, or were there too many variables?

I have always been told Back pressure was essential for torque ??

This is why most exhuast shops do not recommend going any bigger then 2.5inch on an NA V6??

I mean we have experimented with Paddock Bashers and yes you get alot more power at the top end of the Rev range with a Exhaust system with no Back Presure just basically Headers and thats all but torque is next to Zero ! No Torque no Acceleration..
There has to be a balance..

You have that all wrong.

EGR exists as an emissions control device. It slows down combustion rate and lowers the combustion temperature to lower the production of oxides of nitrogen. It achieves this because the exhaust air doesn't contain much oxygen and hence isn't a very good combustion catalyst.

The number one main aim in exhaust design is to get all the spent air out and replace it with clean, burnable, air. This is why people spend hundreds of dollars on extractors and ported heads. You don't end up with a more efficient engine by leaving exhaust gas in the cylinders.

thats what i was thinking and im just another dumb home mechanic
most pre 2000 cars have got it

Good point. Is there anyone else out there running the big 3? I

ezboy is running one, but it is for his future turbo application

As some might know i have an 88 TN turbo'd motor it used to have a
2 ½" exhaust till upgraded to a 3"
and i might say its crap. I had more power with the 2 ½” then the 3”
Until the turbo spools up. Then the 3” is better i believe fre5h 100%, I am 42 years old
and have been doing cars since i was 15 and have always been told you must have back pressure to help clean the waste out of the motor. I used to have a derby car an old 63 ford we took the exhaust off at the flange, (the end of the manifold)
And it used to go crap but put a straight though pipe on and it went better

sorry...... just to add my input into the whole 'tuned length of extractors' part of this discussion..... definately a must! just looking at high power applications ie, Evo's and Type R civics/integras, the extractors on these engines are absolutely crazy! they look like worms, twisting and turning away from the block. your first thought when seeing this is 'why the hell did they do this? it cant possibly be beneficial for the exit of exhaust gases to take such a long and complicated route?' this is to promote efficient pulsing of exhaust gases..... this i know for a fact as mitsu and honda have both spend lots and lots of $$$ on development of these hi-po engines so that they do actually PERFORM.

it wont turn off ok listen here. firstly you need to learn about how a car operates. air goes in air goes out your air filter does notsuck in enough air to feed an engine that is lettin out too much exhaust air . your engine will run faster if there is a consistant flow of the engines "breathing cycle" this is hard to explain over text but **** here it goes,
now wen the exhaust fumes have escaped the combution chamber more air is needed to repeat the cycle but if the exhaust is escaped to quikly the engine needs to force itself to suck in more air quickly. though in most cases it cannot on a standard engine. which is why alot of manufacturers use a EGR Pipe (exhaust gas REturn Pipe.) to "Help" the engine burn faster by reusing a fraction of the exhaust fumes.

Sorry but I couldnt help myself, dude slow down, a lot of what your saying highlights your lack of mechanical understanding.
The EGR system is purely an emissions thing, it reduces particulate emissions by reburning exhaust gas which in theory is supposed to reduce nox and monoxide emissions by simulating a more complete combustion cycle.

If your exhaust is exiting quickly, then you have an efficient engine. If your exhaust is restricted and cant escape then you have an inefficient engine in more ways than one.

The pressure waves created by combustion if not allowed to escape properly can bounce and return to a different cylinder and depending on the revs of the engine create unwanted pressure behind the exhaust valve, preventing exhaust gas escaping the combustion chamber. This creates a lot of heat in the cylinder and around the exhaust valve and prevents the cylinder achieveing full volumetric efficiency of fresh air.

On the flip side, if your exhaust is too large, then your exhaust air speed slows down and becomes basically a quagmire, this can cause the same problem as above and exhaust pressure waves bounce back and forth to no end and cause the engine to stifle.

Frogi was bang on the mark when he said backpressure is a bad thing, you don't want backpressure and racing teams work to remove it with excellently designed extractors and exhausts which truly scavenge gasses with tuned length designs, not just equal length but tuned length.

Having low backpressure doesn't mean having a huge mofo exhaust, it means having the right exhaust, this is the one point I agree with fresh on, too big or too small are both detrimental.

Matthius

Here's my input...

Bling!! look at my cool little drawings.

Ok, the idea that everyone knows, or should know, is that the less an engine has to work doing little things like sucking in air or pushing out exhaust, the more efficiently it runs... hence more power. If you put a straw for an intake and a filter over the exhaust, the thing is going to have to work hard to suck air in and push exhaust out...

...by the way, this is for people who understand the 4-stroke principal. if you don't, go away and learn how it works...

... which is why people use large diameter, high flow, high pressure (super/turbocharged) intakes and high flow exhausts. Easy to suck in, easy to push out, more power for wheels. Backpressure is not good at all. The engine has to work against this, whichis energy that could be put to the wheels. Friction of the pipe's internal surface, bends and interuptions all reduce the flow energy and increase backpressure. Try blowing into a hose thats straight, then bend it. It's much harder to do because of backpressure. When a piston forces exhaust gasses into a pipe, a pressure wave is created which flows out of the cylinder and down a pipe. This, like any travelling object, forms a bit of a vacuum behind it which slows it down a bit, but nothing in comparison to the effects of pushing the air infront of it down the pipe too. This can be seen in the lower picture as attatched labeled standard headers or something. The shorter the pipe is or the larger its diameter, the better the ease of flow is and the less the engine has to do to push all this exhaust out.

The extractors you see on performance cars are usually tuned. This is where the firing order of the car, firing time, pipe length and exhaust expulsion delay are all taken into account so the waves of pressure of exhaust gasses meet up just at the perfect time. This is when one pressure wave is introduced into the main pipe immidiately after another one so it sits in the slip stream or vacuum. The effect of the vacuum sucking the pressure wave in, if the length of the pipe is right, also helps suck out the next pressure wave. The idea is that all of the pipes that enter the main exhaust pipe are timed like this so there is a steady, even pressure flow. Check out the top diagram in the picture below. Very rough drawing, but you get the idea... the + are the pressure waves and the - are the vacuum effects behind them.

This does not eliminate the work that needs to be done to push gasses out but it makes the system much more efficient, especially at the tuned rev range.

It's a bit like an expansion chamber on a two stroke, but in that case the pressure wave bounces back and forward only to suck the next pressure wave out with each reflection. Two strokes have a defined powerband because of this. When the frequency of bouncing waves matches the exhaust pressure wave expulsion rate or firing rate, the thing doesn't have to do any work to push the exhaust out.

The energy in wave form travelling out the exhaust actually does create some suction which is beneficial. Thats why no pipes cause power losses, because the piston has to push its own out, with no help from pressure waves exiting the pipes.

Turbo'd cars need high velocity exhaust gasses to run their turbines which create boost. Boost lag is due to low exhaust velocity at low rpm creating low boost, and higher boost only coming when the exhaust gasses run the turbines at higher rpm to create higher boost.
To get higher velocity gasses, you need a smaller diameter pipe, but this creates backpressure, which is bad, so its a trade off. (low diameter means high velocity because flow = velocity x cross-sectional area and flow is constant). That, and not having a tuned exhaust means the turbine runs irregularly or slower than usual, which means less boost!


...


Phew.... now back to the hydraulics and pipe networks study :D
The exam is tomorrow, what an I doing on here :confused:

Oh well, hope thats helpful.

Cheers,

Danno

My car has a shiney exhaust tip :shifty:

That sounds like fun. Was it possible to construct a mathematical model for this, or were there too many variables?

The way we went about tuning the intake runners was simple. We installed a Kwaka 600 motor on a dyno machine, and made a set of male-female couplings, so that in between these we can insert a different length runners. These were made out of alluminium. Allthough the test had a draw back as we could not mount the injectors closest to the inlet and just lenghten the inlet runner, we had to move the injectors with the manifold, it will be clearear what i mean when i put the thesis up with the photots. HOWEVER, it was very easy to see how the lenght of the runners related to power and tourque curves. For higher tourqe down low a shorter runner was best, with on average 12% differance between it and the optimum (most powerfull) runner for the motor which was found to be 320mm, or something like that. The power curve was observed to shift about 300rpm with each intake runner, in incraments of 50mm.

Once we established this theory, or proved it, we mucked arround with a few different exhausts we had for the engine, we had a set of genuine headers and two different types of extractors. Allthough we did not cover this in the final thesis report, it was very easy to see how much differance these made. We tested the headers on a flow bench to see how much difference there was on each runner and the one that had the closes equal lenght runners, gave the highest power/tourqe combination.

So is back pressure necessary for N/A car, i say yes, i have seen the theory and proved it somewhat. I belive that there is a limit, i certainly don't see how a 2.5" exhaust on a 1.8lt excell is a bonus. LOL.

ok enough.

The other thing to remember with "the scavenging effect" is that some engines will rely on this more than others.

The cam overlap has a little to do with that, the higher the overlap the more it will rely on scavenging to clear the combustion chamber.

Wow interesting thread - lots of information and some of it very impressive, some of it controversial.

I am not going to go into lots of theories and other stuff, just on the experiences we have found from testing no cars which is what we tried.

(A) Exhaust size - we have done numerous vehicles with combo's of 2 1/2" and 3" systems. In all cases these have been done with high flow cat converters eitehr 2 1/2" or 3" units, resonators and mufflers straigth through designs.

Case in point - we took the oruigonal 3" system off my turbo magna, bolted it onto a customers car and took it to the dyno (It had been tuned there previously) and we found that it made very impressive gains. This was used on tested on the hub dyno not the roller dyno and its accuracy and repeatability cannot be questioned.

http://www.mogwa.org/forum/phpBB2/viewtopic.php?t=5375&highlight=rpw+exhaust

Check out the above link because we were just as surprised as anyone on the results. IT was also an interesting discussion on exhaust work that time as well.

SO I stand by what we have stated - for the majority of magna's teh 2 1/2" system is definitly what we recomend for the majority of vehicles for sure.

But for those going that extra mile with stage 2 cams, manifolds and other work the 3" system woudl provide more overall horsepower with larger mods - but woudl with those same mods be a little more sluggish at the lower rpm range due to the nature of the modifications being fitted.

ITs a case of choosing horses for courses as they say.

And of course - our RPW race design extractors, and street design shorty headers, are all fully tuned length systems equal length piping for max horsepower and torque. And are also larger primary pipe diameter units to take advantage of future mods. As shown on the mivec magna - the are definitly a key reason as to why it produced so much horsepower at the AMC dyno day and was also running the 3" exhaust on that same car.

Wow interesting thread - lots of information and some of it very impressive, some of it controversial.

I am not going to go into lots of theories and other stuff, just on the experiences we have found from testing no cars which is what we tried.

(A) Exhaust size - we have done numerous vehicles with combo's of 2 1/2" and 3" systems. In all cases these have been done with high flow cat converters eitehr 2 1/2" or 3" units, resonators and mufflers straigth through designs.

Case in point - we took the oruigonal 3" system off my turbo magna, bolted it onto a customers car and took it to the dyno (It had been tuned there previously) and we found that it made very impressive gains. This was used on tested on the hub dyno not the roller dyno and its accuracy and repeatability cannot be questioned.

http://www.mogwa.org/forum/phpBB2/viewtopic.php?t=5375&highlight=rpw+exhaust

Check out the above link because we were just as surprised as anyone on the results. IT was also an interesting discussion on exhaust work that time as well.

SO I stand by what we have stated - for the majority of magna's teh 2 1/2" system is definitly what we recomend for the majority of vehicles for sure.

But for those going that extra mile with stage 2 cams, manifolds and other work the 3" system woudl provide more overall horsepower with larger mods - but woudl with those same mods be a little more sluggish at the lower rpm range due to the nature of the modifications being fitted.

ITs a case of choosing horses for courses as they say.

And of course - our RPW race design extractors, and street design shorty headers, are all fully tuned length systems equal length piping for max horsepower and torque. And are also larger primary pipe diameter units to take advantage of future mods. As shown on the mivec magna - the are definitly a key reason as to why it produced so much horsepower at the AMC dyno day and was also running the 3" exhaust on that same car.
thank you mate ive been tring to tell these ppl that but no one listend

As some might know i have an 88 TN turbo'd motor it used to have a
2 ½" exhaust till upgraded to a 3"
and i might say its crap. I had more power with the 2 ½” then the 3”
Until the turbo spools up. Then the 3” is better i believe fre5h 100%, I am 42 years old
and have been doing cars since i was 15 and have always been told you must have back pressure to help clean the waste out of the motor. I used to have a derby car an old 63 ford we took the exhaust off at the flange, (the end of the manifold)
And it used to go crap but put a straight though pipe on and it went better
thank you too

I have always been told Back pressure was essential for torque ??

This is why most exhuast shops do not recommend going any bigger then 2.5inch on an NA V6??

I mean we have experimented with Paddock Bashers and yes you get alot more power at the top end of the Rev range with a Exhaust system with no Back Presure just basically Headers and thats all but torque is next to Zero ! No Torque no Acceleration..
There has to be a balance..
thANKING YOU also

Sorry but I couldnt help myself, dude slow down, a lot of what your saying highlights your lack of mechanical understanding.
The EGR system is purely an emissions thing, it reduces particulate emissions by reburning exhaust gas which in theory is supposed to reduce nox and monoxide emissions by simulating a more complete combustion cycle.

If your exhaust is exiting quickly, then you have an efficient engine. If your exhaust is restricted and cant escape then you have an inefficient engine in more ways than one.

The pressure waves created by combustion if not allowed to escape properly can bounce and return to a different cylinder and depending on the revs of the engine create unwanted pressure behind the exhaust valve, preventing exhaust gas escaping the combustion chamber. This creates a lot of heat in the cylinder and around the exhaust valve and prevents the cylinder achieveing full volumetric efficiency of fresh air.

On the flip side, if your exhaust is too large, then your exhaust air speed slows down and becomes basically a quagmire, this can cause the same problem as above and exhaust pressure waves bounce back and forth to no end and cause the engine to stifle.

Frogi was bang on the mark when he said backpressure is a bad thing, you don't want backpressure and racing teams work to remove it with excellently designed extractors and exhausts which truly scavenge gasses with tuned length designs, not just equal length but tuned length.

Having low backpressure doesn't mean having a huge mofo exhaust, it means having the right exhaust, this is the one point I agree with fresh on, too big or too small are both detrimental.

Matthiusyeh i correct \that statement bout EGR pipes for sum reason i was thinking it went bak to the inlet manifold i now remember it went to the exhaust manifold. i had only done a few cars wit the EGR pipe so that was a weak spot in my knowledge

Dudes, just thought I'd point out that there's much more to exhausts than a few pipe diameters etc. There are many factors and it's an exact science to get it right. Primary pipe lengths, diameter and the size of the chrome tip is what us home tuners* talk about. I looked at an exhaust book once hoping that it might have had a generic table of advice for some general engines. Not at all so I thought I'd start reading it properly. There were several chapters explaining things before getting close to what I might have been interested in. Here's a few factors for starters; inlet design, flow rates, piston speeds, rpm, chamber design, piston design, temperature variance, cam design as well as your known things.

It was about an inch think and explained all sorts of weird and wonderful things. The thing is that we don't have a racing budget and for the most part, can only change a few things. One thing most of you have ignored is the actual engine itself. Ever noticed that engines with piggybacks vary the gains a bit? Anywhere from 1Kw to 10Kw gains are typically seen. Know why? Sure, there's the tuner and stuff thrown in but each engine is in a different state of tune which mean that 'x' upgrade doesn't necessarily give 'y' result and this means exhausts too.

Generally a 2.5' could be the way to go but 3' can be good or bad you don't know until you try it on your car.


* tuner is used very loosly here

wow, long thread, thought i would add mu 2 cents.

Firstly. I think what we learnt from this thread is that most people, including exhaust specialists, know what exhausts work because of trial and error, and experience. not because of their intimate knowledge of an engine or physics (im sure there are exceptions).

A while i ago i had a complete exhaust fitted to an otherwise stock 4.1L XF falcon. I personally know the guy that designes and fabricates the exhausts for corsa special vehicles, so i figured he was up to the job.

I asked for a 2.5" system and he said that i would be better off with a 2.25" system. This was not to promote backpressure (although im sure backpressure can be good) it was to reduce restiction (and back pressure) at low speeds.

reduce restriction? i hear you ask. well this is how he explained it to me.

hot air is dense. cold air is less dense. so we want the air to move air out the back before it can cool down. This is done best by keeping the velocity up and diameter within reason. the air on the outside of a big exhaust will cool, effectively slowing all other air around it.


now that makes some sense to me but it could still be completely wrong (proving my point).

what i do know is that my 2.25" exhaust has much better top end power and tourqu than the stock. but it has actually lost something low down. I am sure this would be more significant down low.

So i believe that the exhaust size needs to be matched to the output and desired operating range (rpm) of each engine.

sorry to revive a dead issue, i just didnt think 11 pages was long enough

Hot air is less dense than cold air tho, thats why your car produces more power on a cold night than a hot day :P Your cylinder can only pump so much air, on a cold night this just equals more oxygen molecules per stroke.

Matthius

dont start this AGAIN :confused:

like i said, all crap.

wow, long thread, thought i would add mu 2 cents.

Firstly. I think what we learnt from this thread is that most people, including exhaust specialists, know what exhausts work because of trial and error, and experience. not because of their intimate knowledge of an engine or physics (im sure there are exceptions).

A while i ago i had a complete exhaust fitted to an otherwise stock 4.1L XF falcon. I personally know the guy that designes and fabricates the exhausts for corsa special vehicles, so i figured he was up to the job.

I asked for a 2.5" system and he said that i would be better off with a 2.25" system. This was not to promote backpressure (although im sure backpressure can be good) it was to reduce restiction (and back pressure) at low speeds.

reduce restriction? i hear you ask. well this is how he explained it to me.

hot air is dense. cold air is less dense. so we want the air to move air out the back before it can cool down. This is done best by keeping the velocity up and diameter within reason. the air on the outside of a big exhaust will cool, effectively slowing all other air around it.


now that makes some sense to me but it could still be completely wrong (proving my point).

what i do know is that my 2.25" exhaust has much better top end power and tourqu than the stock. but it has actually lost something low down. I am sure this would be more significant down low.

So i believe that the exhaust size needs to be matched to the output and desired operating range (rpm) of each engine.

sorry to revive a dead issue, i just didnt think 11 pages was long enoughWell said. The alternative to accepting either a single 2.5 for low and mid rpm or a 3" for higher rpm is to run dual 1.3/4 or 2". The smaller pipes have excellent velocity as mentioned but can still move the same or more volume of air as a single larger pipe. I think people struggle to understand that the exhaust is an extension of the extractors - not just a place for the extractors to thoughtlessly dump exhaust while they ask the engine for "more please".

Also on the business of "High Flow Cats", any cat with 400cells per inch is NOT high flow, only 200cpi is accepted as High Flow - don't just take the shop or website's word for it. Cats are not Cats. If in doubt run a larger cat than your pipe - i.e. 3" cat on 2.5" pipe. This is a very common approach.

take the exhaust off behind the extractors and go 4 a drive tell me how well it goes

bet you lose power

toey off the line loose it up top

If that's the case, why do a lot of cars 'drop' their exhausts when they hit the drag strip?

Serious question.. there has to be something in it, or a whole lot of people are horribly misinformed.

Slap him, but only for thinking of putting a big ass exhaust on such a small car. I'd say he'd lose the effectiveness of any scavenging effect. Biggers not always better. It'd sound like a little fart machine though. :bowrofl:

accually, if it is a N14, with the SR20, it responds VERY WELL to a BIG Pipe, 2.5" is not un heard on a nat-atmo SR20.

They perfect exhaust system is a mater of mathamatics. i cant remember the formular, but its all to do with pulse lenghths, you may have heard of tuned length extractors, but do any of you UNDERSTAND them? When a piston fires, a pulse is created, that pulse, is a certain length, if a pipe is the correct length, then the pulse will bounce back to its origen at just the right time, assisting the next pulse. when all the individuall pulses meet at the collector they cancle each other out but create a nother very long and low pulse. as you cant have a narrow pipe 6m long to take advantage of this, then a larger pipe can trick the pulse into thinking it is a long pipe. take a look at F1 cars. they rev to 14K, and have large diameter but very short pipes.

did that help any one?

take the exhaust off behind the extractors and go 4 a drive tell me how well it goes

bet you lose power

toey off the line loose it up top
Actually it goes like a bull possessed! My Dad is a former sprintcar and supersedans national champion. The hotrod had a holden straight six and huge single primary pipes (no collector or exhaust). How did it go? Always beat the V8's off the line (even the ex-nascar blocks), always beat them to the cheqered flag. That's driving FLAT OUT for the whole however many laps the race is.

When the greenies made everyone run exhausts, EVERY car lost power and times went to hell.

Of note too is that these vehicles were all carbie without computer efi or timing.

From Frogi's first post, I got the impression that size doesn't matter (pipe size)...

Well, this from his first link.. has me confused..


We've seen quiet a few "experienced" racers tell people that a bigger exhaust is a better exhaust. Hahaha… NOT.

As discussed earlier, exhaust gas is hot. And we'd like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. We don't want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route. Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe. ...
we know of no accurate way to calculate optimal exhaust pipe diameter. This is mainly due to the random nature of an exhaust system -- things like bends or kinks in the piping....

All I know on the subject is that on a mate's BMW (with a 4" system no less) the head gaskets blew because of it. Backpressure was mentioned then.

I still wonder about that 4" system occasionaly.

im going to say it, even know no body is going to listen and take it on...

with tuned length headers, the ideal exhaust system is none. look at the drag racers, they dont have back pressure. for torque, who cares because i dont mod my car for fuel economy :doubt:

im going to say it, even know no body is going to listen and take it on...

with tuned length headers, the ideal exhaust system is none. look at the drag racers, they dont have back pressure. for torque, who cares because i dont mod my car for fuel economy :doubt:

Amen brother :) exhaust pulses can be helpful, but as soon as they become backpressure - even the word indicates they're a negative force.

Matthius

Amen brother :) exhaust pulses can be helpful, but as soon as they become backpressure - even the word indicates they're a negative force.

Matthius
fk yeah i got through :rant:

ok there have been some good points and some bad points said here. firstly i'l say that test have been done, i think it was rpw or someone the like that did dynno test on a magna between 2.5 and 3 inch systems. the result- no power gain, alos no power loss, just more noise.
secondly, if you disconnect the egr you are likely to lose a bit of power over having it disconnected. now i can't give you scientific reasons, it just does. i speak from experience. i had it disconnected on my sss pulsar and it lost power and fuel economy went out the window. i didn't lose much power up top, but lost bottom end. and it wasn't dramatic. maybe 1hp.
and bigger is only better to a point. i have mates big into the drag scene. 1 of my mates has a nissan exa (1.5l turbo). he has a 2 inch exhaust, a megaflow muffler, (not a cannon). now this might not sound like much, but this thing runs 142hp at the treads. still not enough, how about 13.12 second 1/4 mile? he doesn't want to go to a bigger system because he will lose the scavenging effect. this is what back pressure does. it gives you bottom end. if you go to a huge system you lose bottom end as the back pressure makes it so that the gases at low rpm have enough pressure to 'syphon'. the best annology would be to go talk to your local pump expert. they will tell you if you don't have the right size hose for the pump you won't get optimal performance.
if bigger was always better drag cars wouldn't have exhausts. they spend a lot of time 'tuning' the headers getting them the right length so that the pipes 'suck' the gases from the engine. they can gain or lose big hp by changing the length of the pipes.

but at the end of the day it comes down to the type of driving you are doing. if you are drag racing only, go big. if you sit in traffic most of the time and idle along, keep it sensible. you will get off the line better from low rpm with a reasonable sized exhaust. 2.5 inch is plenty.

also if you are ever going to the drags, when you get there, drop off you rear exhaust section. another mate of mine took his natro r31 skyline from a 14.00 to a 13.50 just by dropping it off, and gained about 20hp.....and the exhaust note was delicious....even if it was about 30db about legal limit. but he is running a 3.0l natro with custom 3 inch exhaust, twin throttle bodies, twin pods with heat sheilds, fully customised ecu, big lumpy cams, custom headers. this thing is basically a speedway engine, and drivetrain in a registered car. and it goes through engines and clutches as quick too!

he doesn't want to go to a bigger system because he will lose the scavenging effect. this is what back pressure does. it gives you bottom end.

The thing is it's not backpressure that increases the scavenging effect at lower rpm, it's gas velocity. At lower rpm the engine isn't pumping out as much exhaust gasses as higher rpm (logiclly), so a smaller pipe diameter will maintain a faster gas velocity improving scavenging.

If the exhaust is too big, the amount of exhuast at lower rpm won't be enough to hold the needed gas velocity to help scavenging because it will we expanding to fill the larger pipe diameter and hence cooling down, once the gas cools it will slow down and accually create backpressure in turn reducing scavenging.

You have to find the pipe size that best suits your needs. For the road it will almost always be one that has the most even spread of torque throught the rev range. You don't want and exhaust that has exellent low down torque but restricts top end and vise versa.

carbon dioxide is wat you breath in true? carbon monoxide is not what you want to breath in that is why it is known as a form of suicide to breath in the gasses emitted from the exhaust.

Not exactly. We breathe OUT Carbon Dioxide!

Not exactly. We breathe OUT Carbon Dioxide!

Well I think there's a percentage of it in the air we breath in. We just breath more of it out once we use up all the oxygen. Anyway who cares.

Well I think there's a percentage of it in the air we breath in. We just breath more of it out once we use up all the oxygen. Anyway who cares.

I cant remember where i read it, but the air we breath has only got something like 3% oxygen in it

The CO2 we breathe in is practically non-existent (it's something like 0.03% of the total air we breathe in).

I cant remember where i read it, but the air we breath has only got something like 3% oxygen in it
Where ever you read that, they were lying.

http://www.mistupid.com/chemistry/aircomp.htm

Where ever you read that, they were lying.

http://www.mistupid.com/chemistry/aircomp.htm

cool thanks for that.

cool thanks for that.
I think you might have heard that or be getting confused when someone exhales or is giving you Expired Air Resuscitation. (i learnt it in First Aid training)

When someone breathes air into someone elses lungs, it is around 5% oxygen from memory which is a darn site less than what you originally breath in, because the lungs absorb the oxygen for it's own needs. That's why when doing E.A.R. you breath into the person more than they would normally breathe themselves. One of the other reasons also as to why they use that hand pump thing to get air into the person... more oxygen goes in.

Off topic I know but I just thought it was worth mentioning.

I think you might have heard that or be getting confused when someone exhales or is giving you Expired Air Resuscitation. (i learnt it in First Aid training)

When someone breathes air into someone elses lungs, it is around 5% oxygen from memory which is a darn site less than what you originally breath in, because the lungs absorb the oxygen for it's own needs. That's why when doing E.A.R. you breath into the person more than they would normally breathe themselves. One of the other reasons also as to why they use that hand pump thing to get air into the person... more oxygen goes in.

Off topic I know but I just thought it was worth mentioning.

So is back pressure good for E.A.R?


Just kidding :D

So is back pressure good for E.A.R?


Just kidding :D

Depends if your running a 2.5" or a 3" system I believe.

I think you might have heard that or be getting confused when someone exhales or is giving you Expired Air Resuscitation. (i learnt it in First Aid training)

When someone breathes air into someone elses lungs, it is around 5% oxygen from memory which is a darn site less than what you originally breath in, because the lungs absorb the oxygen for it's own needs. That's why when doing E.A.R. you breath into the person more than they would normally breathe themselves. One of the other reasons also as to why they use that hand pump thing to get air into the person... more oxygen goes in.

Off topic I know but I just thought it was worth mentioning.

they never taught me that during my 1st aid course :doubt: ....i got ripped :rant: