Hi all,
I was wondering if any of the Sprintex boys have upgraded to a 3" system with dyno results, or have had a reasonable discussion about it with Sprintex themselves, or a credible tuner/workshop.

I'm wondering if there's much to gain in going from a 2.5" system to a 3" (headers-back). Right now I'm mainly interested in results with the 7psi pulley, as I'm not sure when/if i will be chasing more power with forgies, 10 psi and larger injectors.

Currently I have a 2.5" system with 3" metal substrate car, RPW "race" 1 5/8" extractors, straight-through rear muffler and 2x hotdog resos. Given that peak power is occcuring at 6000rpm even with the standard cams, my impression is it must be breathing fairly well up top as is, or I imagine power would be peaking dropping off earlier.

However, I do vagely recall Andrewd (banned a while ago) claiming that he was making peak power at something like 6400rpm with a 3" system and Sprintex@7psi, so I am slightly intrigued.

Cheers.

I think it'd be a good idea - pretty much all turbo Subarus swap out to a 3" TBE for power.

the bigger the exhaust the better, no matter what anyone tells you about backpressure. so go as big as you can manage to keep relatively legal. You would see power rise, how much is impossible to say but noise would increase aswell.

If you desperate to have that little extra power, then go for it, but how often are you giving it 10/10ths where that big of extra flow is really cruical?

I'm running a 3inch stainless system on my TH sports (only major performance mod so far) and to tell you the truth the power band has dropped a fair bit. before i was only running a 2.5inch system and peak power was around 5500rpm, now it's making peak power just on 5000rom. It might not seem like much but it is really noticable on WOT. I would imagine that with a supercharger it would help alot right through the rev range and have already reccomended it to another user on this forum that has charged his magna.

Having forced induction with little or no lag there is no need for backpressure cause your getting near maximum fill in the cylinders at all times... No real need for scavenging.
And a good Cam should sort this.


If you had a switchable supercharger i would suggest against cause the gain you would get with the charger on would not outwiegh the lost performance when turned off.

I'm running a 3inch stainless system on my TH sports (only major performance mod so far) and to tell you the truth the power band has dropped a fair bit. before i was only running a 2.5inch system and peak power was around 5500rpm, now it's making peak power just on 5000rom. It might not seem like much but it is really noticable on WOT. I would imagine that with a supercharger it would help alot right through the rev range and have already reccomended it to another user on this forum that has charged his magna.

I would like to know how much you lost down in the lower rev range....

i didn't loose any power at all, it was a very noticable increase right through the rev range but it just shortenned my rev range. almost like putting a cam in it if you know what i mean.

you still need to get the gases out of the exhaust. The larger the pipe, the slower the gas will move.

you still need to get the gases out of the exhaust. The larger the pipe, the slower the gas will move.

Thats true, you need to keep velocity up, witout restrictiong flow... kinda contradicting

i understand what you're saying but the gasses aren't sucked out by the exhaust, the engine pushes them out so as far as i can understand the above comments have no relevance what so ever on this topic.

Yes the smaller the pipe the quicker the gasses will flow through that pipe and vice versa, but just remember why those gasses are flowing at those speeds.

a supercharged engine will make more torque and hp with a 3inch system no doubt about it.

engines with forced induction are affected little by back-pressure or lack of. There is such a large mass of exhaust gases leaving the engine that back pressure plays little part. On a non-forced induction engine, back pressure plays a vital role in helping coax the exhaust gases in the right direction.

On a non-forced induction engine, back pressure plays a vital role in helping coax the exhaust gases in the right direction.

Sorry but I don't agree with this. Like the old power/torque debate, I feel the old backpressure myth is one which constantly rears its ugly head.

Basically at an optimum level of gas velocity, backpressure is minimal, and this is the ideal situation. The lesser the backpressure, the lesser the pumping loss, and therefore more power/efficiency.

For a given volume of gas flow if the pipe is too big, velocity is too slow, and backpressure is created. However, if the pipe it too small, backpressure will also be created. What you want is to find the balance where you are achieving good velocity with minimal backpressure. However, as a car engine does not produce a constant volume of gas velocity, but infact it varies greatly depending on rpm/load, it is all about trying to find the best compromise for the situation.

I believe 2-stroke motors in fact need some backpressure to work properly, however for 4-stroke motors, it's a case of the less backpressure the better at all times.

Also it it important to remember exhaust gas does not come in one steady flow, but in a complex series of pulses with pressure waves. Basically backpressure is created when the pulses collide, a good exhaust system allows the pulses to escape with minimal interaction with each other (besides "scavenging" when applicable).

In turbo cars, even with a well-designed exhaust the turbo will always create plenty of backpressure which is inescapable (power is never "free"), but with an NA motor, a well-designed exhaust system will offer minimal backpressure for the conditions in question.


I'm running a 3inch stainless system on my TH sports (only major performance mod so far) and to tell you the truth the power band has dropped a fair bit. before i was only running a 2.5inch system and peak power was around 5500rpm, now it's making peak power just on 5000rpm

This really confuses me. Generally if you run too big an exhaust for the motor, the result is at low rpm/load gas velocity is too slow, to the point that backpressure may form. But unless the exhaust is STUPIDLY big, only bottom-end will suffer, not top-end.

Are you sure about this apparent drop in top-end power? Is this from looking at dyno graphs, or from the "bum-dyno"? Are you sure it isn't something else like a stuffed cat? What you describe is exactly what I felt when my cat collapsed, like the top 500rpm or so chocked.

i would say 3" would be a good size, but i would strongly suggest a decent set of extractors.. or at least a decent set of collectors on the 'race' extractors.. from what i can see there just an ordinary bash collector.. not a tapered merge cone.. thats where you get the power from..

That's great that people *still* misuse the term 'back pressure'. Back pressure would be better referred to as a lack of gas movement, or flow retardation. Anyway, the key is velocity and keeping exhaust velocity at it's peak and making it occur at a useable rpm. I'm not going to rehash the pressure reading at peak torque etc instead I will answer your question:

Running DUAL pipes of 2" will give you the same cross-sectional area as a single 3" BUT it is easier to control drone and note using dual systems. Your cat converter should be 0.5" larger than your exhaust pipe cross section i.e: 3" pipes or 2.2" pipes use a 3.5" cat. It's all about minimising flow restrictions while maintaining peak velocity. The heat of the expanding gas and the correct sized exhaust is the MAIN driving force behind gas flow, with minor consideration to resonance/pulse tuning etc.

The Sprintex AWD ran dual 2.5"s but I think it was split at the rear. Which isn't the worst thing. Consider a set of Hurricane headers, 3.5" cat, 3" pipe, resonator (louvred internally with fully glass packed body), split at the rear axle into dual 2" or even 2.25" pipes (larger to compensate for the losses thru the additional bends at the rear of the car. 2.25" also presents more Muffler options. Make sure any muffler you choose is fully glass-packed and doesn't have a resonance chamber!

Enjoy. :cool:

AFAIK hurracaine only use 1.5" pipe at least all the ones i have seen do..

i would seriously be looking at the extractors and improving on them.. THAT is where power is made, collectors, pipe size, steps, merge.. everything.... the rest of the exhaust doesn't make nearly as much difference as what somthing so close to the head will make..

Are you sure about this apparent drop in top-end power? Is this from looking at dyno graphs, or from the "bum-dyno"? Are you sure it isn't something else like a stuffed cat? What you describe is exactly what I felt when my cat collapsed, like the top 500rpm or so chocked.

ok this is the last time i am going to say this, and i'll even put it in capital letters.

I HAVE NOT LOST ANY TOP END POWER, MY POWER BAND HAS CHANGED AND NOW MAKES MORE POWER AT A LOWER RPM.

and yes this is from me only feeling the power difference and the fact that it runs out around 5500rpm unlike what it used to do and rev cleanly past this point, not from a dyno read out. i don't even know why so many people carry on about torque figures anyway, you can't measure it on a chassis dyno, this magical torque figure that people give is just tractive effort. The only true way to measure how much torque is by using an engine dyno.

as for my cat, no there is nothing wrong with it. the power increase way apparent as soon as i left the exhaust shop on my way home after finishing the system.

Is it not true that if you keep velocity UP in the exhaust without going too big the speed of the gasses moving in the exhaust actually help the cylinder empty, and also help the incoming air enter when the valves overlap??? Sucking more of that presious air/fuel into the motor.... More fresh gas means more power....
Called scavenging.... And is very valuble in a NA motor...
But i could be wrong.....

I dont see how 3' can be benificial on a 3.5ltr that only revs to 6000rpm...

maybe if it reved to 8-9000.....:nuts:

EDIT this is not an attack on you ARS55 just a discusion maker...

Is it not true that if you keep velocity UP in the exhaust without going too big the speed of the gasses moving in the exhaust actually help the cylinder empty, and also help the incoming air enter when the valves overlap??? Sucking more of that presious air/fuel into the motor.... More fresh gas means more power....
Called scavenging.... And is very valuble in a NA motor...
But i could be wrong.....

I dont see how 3' can be benificial on a 3.5ltr that only revs to 6000rpm...

maybe if it reved to 8-9000.....:nuts:

EDIT this is not an attack on you ARS55 just a discusion maker...

only in an extractor like situation, the gases exiting the other cylinders have a scavenging effect on the cylinders.

only in an extractor like situation, the gases exiting the other cylinders have a scavenging effect on the cylinders.

only at a specific RPM.... this is where you TUNE your exhaust.....

See im not saying bigger than 2.5 isnt better... BUT the flow rates of 3' compared to 2.5 are quite a bit... so maybe a 2.75 pipe diam would have been more BENFICIAL for the engine size in question...

But like ARS55 said he has more pull up top that i can beleive because the 3' would prefer the higher rpm band, but i cant believe that he has more down low....aswell. there is nothing that will improve a rev band like that. Low+ Middle OR Middle+ Top Rpm

I went from 2.25 to 2.5 mandrel and i felt a loss BELOW 2-2500 rpm but then it kicks a gets outta there the best a 3.0ltr single cammer can...

Now can you see what i'm saying.

Sorry but I don't agree with this. Like the old power/torque debate, I feel the old backpressure myth is one which constantly rears its ugly head.

Basically at an optimum level of gas velocity, backpressure is minimal, and this is the ideal situation. The lesser the backpressure, the lesser the pumping loss, and therefore more power/efficiency.

For a given volume of gas flow if the pipe is too big, velocity is too slow, and backpressure is created. However, if the pipe it too small, backpressure will also be created. What you want is to find the balance where you are achieving good velocity with minimal backpressure. However, as a car engine does not produce a constant volume of gas velocity, but infact it varies greatly depending on rpm/load, it is all about trying to find the best compromise for the situation.

I believe 2-stroke motors in fact need some backpressure to work properly, however for 4-stroke motors, it's a case of the less backpressure the better at all times.

Also it it important to remember exhaust gas does not come in one steady flow, but in a complex series of pulses with pressure waves. Basically backpressure is created when the pulses collide, a good exhaust system allows the pulses to escape with minimal interaction with each other (besides "scavenging" when applicable).

In turbo cars, even with a well-designed exhaust the turbo will always create plenty of backpressure which is inescapable (power is never "free"), but with an NA motor, a well-designed exhaust system will offer minimal backpressure for the conditions in question.



Maybe engine capacity has something to do with it, but I have had experience tuning smallish 4 cyl engines (1.6-2.0), and there is definately a loss right across the rev range when moving to a 2.5" system from roughly 1.8".

i guarantee that a 3inch pipe will do nothing for a sprintexed magna except make noise and lose torque.

Andy, I think this question is probably betted suited to pf.com, rather than aussiemagna. Those guys seem to know alot of technical in depth facts (assuming you havent posted their yet).

Basically, I was always led to beleive, that on a NA motor, bigger exhaust isnt always better, yes, you are increasing capacity, however, you are decreasing velocity of the exhaust gasses, often leading to poor results, or less power.

I know that on a turbo engine, bigger tends to be always better (within reason ofcourse) because the turbo is effectively "pushing" the exhaust gasses out.

As for a supercharged setup, I would think (and i mention think, because I dont know for a fact), that the optimum level lies somewhere between that of an NA, and Turbo motor.

As for your particular case, I think the money would be better spent on upgrading your cam, and then, maybe, changing exhaust latter on.

i guarantee that a 3inch pipe will do nothing for a sprintexed magna except make noise and lose torque.

so you've had a 3inch exhaust on a magna with a sprintex?

results please.

Sheeesh,

Since if was possible for you to gain power where it shouldnt be available considering your setup,whos to say a supercharged 3.5 wouldnt have a "better power band" with a 2.5" instead of a 3" pipe??????,It`s like sticking a huge duration cam in a engine and saying you picked up a heap of bottom end over a short duration cam,never usually happens,but hey,if you feel it you feel it i spose

In my experience,I have always sacraficed low end torque when going bigger in exhaust size,this ranges on engines from 5 lire V8`s to 1MZ-FE V6s,so a broad range i say,but top end normally always improves,these days i will always go for torque for street driven vehicles over outright power anyday,it makes for a much more comfortable drive,you can stick peaky engines up your bum,i like big lazy engines that dont need the ring revved out of them to make decent power and torque

Steve

remember when you say tune, are you actually referring to changing timing and fuel maps on the engine after the exhaust install. I can give you plenty of examples of where low end torque has increase on the same motor while jumping up .5inch at a time. Granted the car was a 16v DOHC 1998cc NA. The final exhaust chosen was 3.5inch as it made the most power with the least noise (granted it is a track car) but 4 inch only gained 1.3hp... which is well inside the margin of error for a dyno, but the niose was unbearable.

At no stage did the low end torque drop off, or even dip below the previous benchmark and we started with a 2" system. Every time the exhaust was changed, the tune was slightly altered (usually a point or 2 more igntion advance and even able to trim some fuel out as the chamber was better scavenged on the last system)

The car is far from a daily, but was making good low down torque (as much as 2ltrs can have) when dribbled around the city roads

Depends on amount of fluid being pumped and every single restriction in the system. Pipe englargments/shrinking bits, angle bends.

The 3" will probably improve it in this case but you're guessing pretty safe bet though.

so you've had a 3inch exhaust on a magna with a sprintex?

results please.

Yeah results kthx.

With turbo cars you tend to go larger as lesser restriction= more power, now being supercharged is very different, yet similar as its still forced induction. I dunno how about someone with a kit go and switch from a 2.5 inch system to a straight 3inch and get it dyno'ed. Will be the only way to solve this i assume.

Sheeesh,

Since if was possible for you to gain power where it shouldnt be available considering your setup,whos to say a supercharged 3.5 wouldnt have a "better power band" with a 2.5" instead of a 3" pipe??????,It`s like sticking a huge duration cam in a engine and saying you picked up a heap of bottom end over a short duration cam,never usually happens,but hey,if you feel it you feel it i spose

In my experience,I have always sacraficed low end torque when going bigger in exhaust size,this ranges on engines from 5 lire V8`s to 1MZ-FE V6s,so a broad range i say,but top end normally always improves,these days i will always go for torque for street driven vehicles over outright power anyday,it makes for a much more comfortable drive,you can stick peaky engines up your bum,i like big lazy engines that dont need the ring revved out of them to make decent power and torque

Steve

What you guys are failing to see, is that forced induction is VERY different to N/A.

FI is all about getting rid of the exhaust as quick as possible, because the positive pressure on the intake side of things, can/will overcome imperfections in the inlet.

I definatly think 3" on any magna with forced induction. I believe that a 2.5" is just restricting it.

I mean, my EVO is running a 3" exhaust from the cat back, and it is a 2L 4cyl.

I know everyone is going to say something about turbo vs. supercharger, but hey, you guys fail to realise, that the turbo IS the restriction in my exhaust.

What you guys are failing to see, is that forced induction is VERY different to N/A.

FI is all about getting rid of the exhaust as quick as possible, because the positive pressure on the intake side of things, can/will overcome imperfections in the inlet.

I definatly think 3" on any magna with forced induction. I believe that a 2.5" is just restricting it.

I mean, my EVO is running a 3" exhaust from the cat back, and it is a 2L 4cyl.

I know everyone is going to say something about turbo vs. supercharger, but hey, you guys fail to realise, that the turbo IS the restriction in my exhaust.

Turbo vs supercharger does make a big difference. Remember, the turbo is connected to the exhaust, and the piping after the turbo has very little effect on any scavenging effect made my the exhaust manifold. The extra pressure the turbo places on exhaust gases means that Turbod cars tend to need larger exhausts to stop any restriction.

Supercharged cars are very different. They still need the exhaust to provide ample velocity inorder to expell the gasses in the correct fashion. The extractors scavanging effect is also quite important.

So, as I said above, Supercharged cars lie somewhere between Turbo, and Na cars interms of the exhaust side of things.

a general rule with extractors on a S/C engine.. what works well on a NA engine, will work reasonably well on a S/C engine.. usually the next size up in pipe like if you have 1 1/2" primaries you would use 1 5/8" etc etc.. similar principal applies to Nitrous fed engine.. you can play around a little with lengths and steps in the overall length if you like, but i'm just giving rough examples..

a prime example would be a set of 1 7/8" 4-1's on my Bro in laws 2.0L escort (before we did the 2ZZ-GE conversion) the pacemakers were a bit better in normal operation (twin webbers, bit valves, big ports, high comp, big cam etc et) but with the gas shot they chocked the engine.. with the bigger custom 1 7/8" pipes.. it was a little rough and doughy low/mid.. but on gas...... wow..... made a massive difference...

Turbo vs supercharger does make a big difference. Remember, the turbo is connected to the exhaust, and the piping after the turbo has very little effect on any scavenging effect made my the exhaust manifold. The extra pressure the turbo places on exhaust gases means that Turbod cars tend to need larger exhausts to stop any restriction.

Supercharged cars are very different. They still need the exhaust to provide ample velocity inorder to expell the gasses in the correct fashion. The extractors scavanging effect is also quite important.

So, as I said above, Supercharged cars lie somewhere between Turbo, and Na cars interms of the exhaust side of things.

Sort of.

See, It tells all in recommended cam spec's for a supercharged motor. Basically, you want a set of cams with big overlap like an N/A Car, BUT you want a larger exhaust side.

You use the blower to PUSH the gasses through the exhaust ports, and into the exhaust, maintaining velocity.

I believe 3" is warrented.

IMHO 2.5" is too restrictive on a 3.5L V6 making 180kw @ the wheels.

I believe the car will breath a bit easyer with a 3".

After that Andy, throw in a nice set of cams. :D

My car is getting a 3 inch system on monday, the collectors to the cat have already been done in 3 inch so it just the cat back being done. ATM i'm making around 200kw with peak power just over 5,000RPM where in Chisholm's case he is making peak at 6,000RPM. I have recently found out my zorst is only 2 1/8 over the rear wheel which is gay, the car makes a mountain of power up to 5,000RPM and then dies in the ass. I wont have dyno results but i will have quater mile results next week. Last time at the drags i ran 104MPH trap speed so we can all use that to compare if it makes more power

My car is getting a 3 inch system on monday, the collectors to the cat have already been done in 3 inch so it just the cat back being done. ATM i'm making around 200kw with peak power just over 5,000RPM where in Chisholm's case he is making peak at 6,000RPM. I have recently found out my zorst is only 2 1/8 over the rear wheel which is gay, the car makes a mountain of power up to 5,000RPM and then dies in the ass. I wont have dyno results but i will have quater mile results next week. Last time at the drags i ran 104MPH trap speed so we can all use that to compare if it makes more power

wow he posts again! lol but yeah remember though he has a different motor as in cam spec, compression and the standard ralliart headwork, that accounts for something

wow he posts again! lol
yeah, i got the saying "work to live, not live to work" a bit confused over the last 3 months :rant:

My car is getting a 3 inch system on monday, the collectors to the cat have already been done in 3 inch so it just the cat back being done. ATM i'm making around 200kw with peak power just over 5,000RPM where in Chisholm's case he is making peak at 6,000RPM. I have recently found out my zorst is only 2 1/8 over the rear wheel which is gay, the car makes a mountain of power up to 5,000RPM and then dies in the ass. I wont have dyno results but i will have quater mile results next week. Last time at the drags i ran 104MPH trap speed so we can all use that to compare if it makes more power

Jase sounds like your top-end is being chocked pretty good (since peak power should be more like 6200rpm for you, as long as the blower isn't running out of efficient flow), should see good results with a 3" system :)

I assume that 104mph was when it has the 7psi pulley and no water injection? I'd be expecting a fairly marked improvement with 10psi, WI and presumably a better tune.

Was beginning to wonder what happened to you Jase :P

I expect to see a detailed thread on your new build!

Jase sounds like your top-end is being chocked pretty good (since peak power should be more like 6200rpm for you, as long as the blower isn't running out of efficient flow), should see good results with a 3" system :)

I assume that 104mph was when it has the 7psi pulley and no water injection? I'd be expecting a fairly marked improvement with 10psi, WI and presumably a better tune.

Was beginning to wonder what happened to you Jase :P

I expect to see a detailed thread on your new build!
No that 104mph was with 10psi, but i did run around 102pmh with 7psi. The difference is i got 13.6 with 7psi and 13.1 with 10psi. The water meth kit hasnt been done yet so even with the new zorst i wont be retuning it until i get the water done.

Why dont you bring your car out for a race this wednesday night, I'll be there aiming for a 12 second pass and you'll get a mid 13 easy with your car

No that 104mph was with 10psi, but i did run around 102pmh with 7psi. The difference is i got 13.6 with 7psi and 13.1 with 10psi. The water meth kit hasnt been done yet so even with the new zorst i wont be retuning it until i get the water done.


Sports did 13.5@104mph on 7psi, and apparently his clutch was slipping a little. So I'm surprised you only managed 102mph, and you are obviously not beginner at the drags. Although was this in unfavourable conditions like summer heat and/or oncoming wind?

Eagerly awaiting your results with the 10psi, 3" exhaust and WI, as I will probably end up following suit if it works out well for you:P



Why dont you bring your car out for a race this wednesday night, I'll be there aiming for a 12 second pass and you'll get a mid 13 easy with your car

No can do, but will definantely hit up the drags soon :)

Sports did 13.5@104mph on 7psi, and apparently his clutch was slipping a little. So I'm surprised you only managed 102mph, and you are obviously not beginner at the drags. Although was this in unfavourable conditions like summer heat and/or oncoming wind?

Eagerly awaiting your results with the 10psi, 3" exhaust and WI, as I will probably end up following suit if it works out well for you:P



No can do, but will definantely hit up the drags soon :)

Sports has always had amazing 1/4 times no matter what mods he has done.. however there is no way I personally could launch my car like he does. mainly for feer of breaking things. and it's just not how i want to treat my car.. I will settle for a slower 1/4 time.. but a happy car lol.

I like this thread.. im contemplating looking at a 3" exhaust aswell, however i don't know if the performance gain will be worth it as I love how it sounds at the moment... and performance isn't everything for me.. as u can tell :badgrin: