exhaust backpressure!

[bl1tzk1213g]

i asked for how much a custom exhaust for a 97 eclipse gst. The guy said $289 with magnaflow exhaust. Then i asked if its the same for the 3" piping. He then told me they cant put 3" piping on my car or i will lose backpressure. He told me id lose power and they could only put 2.5" press bent pipe. He even asked me what kind of engine i have and mods. I said it was turbo! Still no go, backpressure... Is he wrong or am i just stupid?

what do u guys think about their press bent 3"? the muffler must have 3" inlet right? do u think they might use a 2.5" inlet and 3" pipe? how about tsudo catback? well its $300+ shipping and tax included but my brother said that difference will only be like 1/8 inch and wont really notice on street cars. planning on evo 16g get atleast 350-400whp thanks

[spyderturbo007]

Originally Posted by bl1tzk1213g

Is he wrong or am i just stupid?

He's an idiot.

The best exhaust for a turbo, is no exhaust at all.

[LouieAWDTSi]

If you are really looking to hit 350-400 hp...you hsould just spend the money now on a 3in turbo back madrel bent exhaust. Turbo's don't want back pressure. To reach that goal you are going to need all fuel mods,turbo, tuning, and FMIC at least. If that is truly your goal then just go with the madrel bent 3in off the internet or what not. If you really are just looking to make some more power and like a 13 sec car, you could always just get the press bent done if it saves you cash.

[bl1tzk1213g]

thing is, my mom wont let me use her atm/card online cause she was told my by my aunt about and scams =/ but my brother in law uses ebay a lot. ok now i gotta open my new account to but it. thanks for the info

[Black97GST]

yeah print this thread out, take it to that guy and show him how much of an idiot he is! what a dumb ass! lol

[Skugulgurk]

I used to work on a lot of older muscle chevys (Nova, chevelle, camaro). I also raced the bracket series with my 70' nova. I tried a lot of different exhaust combinations. I was even dumb enough to think that open headers would not only sound cool but would make my car faster. The track proved that with no backpressure I lost up to five tenths in the quarter. I also had other competent "ricers" tell me that the reason their civic was faster than the other civics was because of the fact that the incompetent civic drivers would spend all their money and put a huge 3" exaust on top of a muffler designed to pull air through the system. I've seen this proven. Does a turbo really provide sufficient backpressure to where the exhaust doesn't matter? Again I have no experience with forced induction so please excuse me if I'm being ignorant.

[tfoti]

Originally Posted by Skugulgurk

Does a turbo really provide sufficient backpressure to where the exhaust doesn't matter? Again I have no experience with forced induction so please excuse me if I'm being ignorant.

Best summed up by our resident DSM expert:

Originally Posted by 95_GSXRacer

The turbo provides more than enough "backpressure," in fact too much (the reason we all switch to bigger hotsides eventually). But in summary, velocity is good, backpressure is ALWAYS bad.

[Thor06]

There is a really good article on backpressure on dsmtuners.com... I will find it tonight when I have time to search for it.

[kjewer1]

Originally Posted by Skugulgurk

I used to work on a lot of older muscle chevys (Nova, chevelle, camaro). I also raced the bracket series with my 70' nova. I tried a lot of different exhaust combinations. I was even dumb enough to think that open headers would not only sound cool but would make my car faster. The track proved that with no backpressure I lost up to five tenths in the quarter. I also had other competent "ricers" tell me that the reason their civic was faster than the other civics was because of the fact that the incompetent civic drivers would spend all their money and put a huge 3" exaust on top of a muffler designed to pull air through the system. I've seen this proven. Does a turbo really provide sufficient backpressure to where the exhaust doesn't matter? Again I have no experience with forced induction so please excuse me if I'm being ignorant.

Most poeple that post comparisons to V8s really show thier ass, thanks for the intelligent contribution. Quite refreshing.

My statement quoted above is the super short version, I know I have posted more involved responses on the topic in this forum. But to stick to real world examples rather than theory... People with turbo DSMs always pick up HP with larger exhaust piping. People running 10s or better have also measured gains going from 3 inch to 3.5". People that have dropped thier catbacks and run open downpipe (equivalent to open header, close as possible anyway ) have picked up several mph. A local DSMer picked up 4-5 mph running mid 10s at ~130. All of the serious DSMs, shep for example, all run a straight pipe out the side of the car, or with just one bend. Look up pics of sheps setup. His turbo faces front/back so the inlet is "in" the front bumper (CAI anyone? ). There is one bend to dump the exhaust right out the side of the car. No DP, no mufflers, no backpressure whatsoever. They typically run a pipe size larger than the turbine outlet size, so there can really be no measureable back pressure. Shep is running 8.13 at 178, something around 1200-1400 hp.

The turbo is definitely the major restriction in the exhaust system. Look down the turbine inlet. The scroll area is very small. Nowhere near any exhaust piping diameter. And its imediately after the head. You can't even get much in the way of exhaust scavenging like you can with headers on NA cars, since the exhaust manifold pressure is always higher than intake manifold pressure at WOT, to illustrate how restrictive the turbo is. Exhaust manifold to intake manifold pressure ratio is a huuuge part of the power production puzzle. No need to go into it, but it's significance is important in making this point.

[david-b]

^^^ That is why Kevins the man! Without a doubt.

With a N/T car, this is different. Maybe its only this way with smaller 4 banger engines, but i know from experience that back pressure is needed for N/T. When doing my exhuast, the bolts from the DP to the cat came loose, and I pretty much lost my whole cat and cat-back... Still hanging, but not connected at all. Anyways, there was a HUGE loss in any kinds of performance. I could floor it, and the car just sat there. I don't see why back pressure is needed for one kind, but not the other kind. I understand the turbo makes its own or whatever, but i just don't get it. I've read up on it too, but still no go.

[Skugulgurk]

Originally Posted by 95 GSXracer

Most people that post comparisons to V8s really show *their ass, thanks for the intelligent contribution. Quite refreshing.

I will try to keep the V8 comparisons to a minimum. It is just all I have to compare with at the moment. I don't have much experience with smaller import engines yet. Thanks for the help though.

[kjewer1]

[quote=david-bWith a N/T car, this is different. Maybe its only this way with smaller 4 banger engines, but i know from experience that back pressure is needed for N/T. [/QUOTE]

The rant I have done in the past can be entered here It is still no backpressure that you need. It's velocity. I thought I posted more about it, but all I can find is this:

False. Backpressure is never good. ashah000 got it right. You want velocity, to exploit the scavenging effect and pull more aif/fuel in during valve overlap. Smaller pipes increase velocity, thats physics. Increased backpressure is a sideeffect of smaller pipes. So unfortunately poeple confuse the two. Its also possible to increase velocity efficiently, meaning less increase in backpressure pre increase in velocity. Thats the whole trick...

You want the exhaust to travel at high velocity in NA cars to increase scavenging. Backpressure is pressure in the exhaust system that fights the scavenging effect. Those are the simplest terms I can put it in. The trouble is they often go hand in hand as mentioned above.

But to tie it into my previous post, consider the scavenging effect you get with NA motors, header tuning etc. With a turbo there can really be no scavenging to pull more intake charge in during valve overlap thanks to the high exhaust manifold pressure. When exhaust manifold pressure to intake manifold pressure gets too high you are going to get reversion, which is basically the opposite of scavenging. Fluids will move from an area of high pressure to an area of low pressure. Imagine this scenario: intake and exhaust valves both open (overlap), exhaust manifold pressure 40 psi, intake manifold pressure 25 psi. Which way is the air/exhaust going to travel? I believe it was corky bell that said getting exhaust manifold pressure below intake manifold pressure is where the F1 cars really start to make ridiculous power/liter. This is all also the reason why turbo cams tend to run less overlap than NA cams. Its also why people take time to put in anti-reversion measures when building DSM motors/heads. I typically leave the exhaust port a little smaller than the exhaust manifold runner to create a step that helps resist backwards flow. Etc.