I hit Heidelburg Mitsubishi dealer to look at some Magnas and they had an exec done up with exhaust, lowered, mags, etc.
He was showing me how good the exhaust was and said listen to the exhaust suck in when I take my foot off the accelerator. He told me that back pressure was good.

Is this BS? I would have thought the more air you get out of the exhaust the better?

I can't say Im an expert on car exhausts, but from my knowledge, on any naturally aspirated engine exhausts you do need a certain amount of back pressure, this is why you can put an exhaust on a car that is to big for that certain car, re****ing in power losses.

Im sure some one else can go into more depth and explain it more fully then myself. But basically, back pressure isn't such a bad thing, you just don't want too much of it.

Haha... Be Very careful what they try to sell you.... Because i think I got ripped off a bit because of just the looks.

here is what I think you should pay attention to;

1) Engine Odo
2) Engine sound under some load
3) Look under the bonnet, CHECK ENGINE MOUNTS, bring a torch to see the rear mount.
4) listen to the Engine idle, does it sound refined or rough or
5) You say it's lowered, check what springs they are and whether they changed the shocks or they just changed the springs.
6) Make sure there isn't excessive wear on outter edges of your tires,
7) Stick your head under the front of the car, Look Very carefully for any moist patches, if its' not too hot, run your finger or a tissue across the sumps.
8) You say it has an Exhaust done, Measure the inner diameter of it if it is a cannon, if not, is it just a tip or Lukey or what, find out? also if it's a cannon, Make sure the Piping from the Cat back is 2.5" and not some dodgy links of Piping from various pipes. Make sure you're happy with the level of noise from the exhaust, Don't think that you can get used to it if your test drive was drony.
9) During your test drive, listen carefully and try to feel for vibrations and remember what RPMs are when the noises or vibrations happened. Also, test your brakes, make sure it doesn't shimmy or shudder during light or heavy braking.
10) make sure gear changes are smooth if it's an Auto or make sure that the clutch doesn't slip if it's an Manual.
11) should always check the fluid once you've warmed up the car, Check Engine Oil and Transmission fluid and brake fluid. Coolant can be checked by observing from the resorviour near Battery.
12) check battery, if you have a Volt meter, bring it and make sure it's at least 12.4V on its own. if it's lower than that, you should ask the dealer to replace it with a better battery or at least one that is better charged.
13) Check your door seals and windows, and TAKE your time to look at every single spot on your wind screen for chips or scratches, GET them to replace it if you see even the slightess chip. It's easily not road worthy. If it's Tinted, look closely for scratch marks on the inside of your window glass.
14) Check your carpet, look for stans, look for broken glass bits, If you see small glass pieces in some corner of your carpet, that suggests the windows have been smashed recently.
15) Look from the outside, look at the reflections of your panels and see if there's dents and if they align up.
16) Check that all your external lights work.
17) Check that all your internal lights work.
18) look closely at your console, does it have scratches?
19) push all the buttons you can push inside the car, make sure you are happy with them.

finally, NEVER EVER Look pleased with the car, else you'll give the salesman an excuse to not drop the price.

Good luck, good hunting.

oh, Always point out bad things about the car as soon as you find them, don't hold back the bad things, But hold back the good things about it. Don't look pleased with the car!

Arguing about back pressure is like arguing about religion... IMHO low back pressure doesn't make a difference except if you go for a ridiculous size like a 5" pipe, whereby the gas cools down sufficiently that you don't get the draft effect of cool air drawing hot air out.

Changing pipe sizes is mostly done to get a desirable sound out of the exhaust, or to increase flow when back pressure is too high.

He was showing me how good the exhaust was and said listen to the exhaust suck in when I take my foot off the accelerator. He told me that back pressure was good.

Is this BS? I would have thought the more air you get out of the exhaust the better?

Sorry my last post wasn't what you asked. About the sucking sound, He is trying to say that there's burble from your exhaust, I really Doubt it. Without tuned extractors/headers, You'll only get a bit of a soft back fire. Whereas burble is damn sexy thing to have, but not easy to achieve, only achieveable if you have an independent dual exhaust system or if you have tuned extractors, burble is created by the pulsating behaviour of tuned length extractors hence producing out of phase pulsations at the muffler.

Arguing about back pressure is like arguing about religion... IMHO low back pressure doesn't make a difference except if you go for a ridiculous size like a 5" pipe, whereby the gas cools down sufficiently that you don't get the draft effect of cool air drawing hot air out.

Changing pipe sizes is mostly done to get a desirable sound out of the exhaust, or to increase flow when back pressure is too high.

Whos arguing about back pressure? And also are you an exhaust expert? Just out of curiosity. All the fellas that I've spoken to at exhaust shops, which is a few, seem to think that even just 1/2 an inch in pipe diameter can be the difference between to big and just right. :?

I know your not talking about exhaust here but ill add this.

What you need is a good exhaust velocity to 'suck' the gas from the cylinder creating a vacumn before the exhaust valve shuts so more fresh air enters on the next intake stroke. To get good exhaust velocity you need a smaller pipe. Bigger pipe, the more cross sectional area, the slower the exhaust gas will travel. So its not really back pressure is good for the engine, back pressure is a result of a smaller pipe. Its a trade off but typically car manufacturers use smaller exhausts for cost savings/ reduced exhaust noise/ other silly reasons.

Back on topic now haha.

as far as im aware backpressue IS the topic

all i know is that increasing the stock sized exhaust on the 2.6l magnas (by an inch or so) will reduce the low-down torque by alot, but increase top end at the same time... goes with most cars though... not srue about 4 valve per cylinder cars tho, maybe the difference is much less

IMHO backpressure is very important, but what the dealer was describing is just back fire, when the engine drops suddenly in revs, in my car i get a fair amount of back fire,
you can't really desbribe backpressure, but if the pipe is too big, the exhaust wont have the sucking in effect , just like extractors, which are normally designed to be a bit too bit so it sucks in the gases rather than letting them flow!

no back pressure in a turbo car will make the turbo not spool or too much lag!

there is a reason why exhaust pipes have to be of the correct dimension!

Backpressure is basically the amount of resistance your exhuast system has when trying to expell exhaust gas.

In a nutshell, when it comes to naturally aspirated cars, more backpressure means better low down torque but will become restrictive quite quickly robbing you of top end power in the high rev range. The less backpressure you exhaust system has means it won't have as much torque down low but won't be restrictive at high RPM's.

Generally the stock exhuast system is designed to masimise low down torque while meeting noise and emmision standards. Putting a higher flowing exhaust on will allow you to reduce backpressure and gain more power higher in the rev range.

Adjusting your backpressure is a matter of choosing your exhuast sizing a muffler carefully.

Without tuned extractors/headers, You'll only get a bit of a soft back fire. Whereas burble is damn sexy thing to have, but not easy to achieve, only achieveable if you have an independent dual exhaust system or if you have tuned extractors, burble is created by the pulsating behaviour of tuned length extractors hence producing out of phase pulsations at the muffler.

I've got quite a nice burble coming out of mine - mind you, my definition of burble may be different to yours.

Arguing about back pressure is like arguing about religion.

So true - this will become a flame war in no time.