Low back-pressure is bad for non-turbos - Saab 9000 Bulletin Board - Saabnet.com
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Low back-pressure is bad for non-turbos
Posted by BillJ (more from BillJ) on Mon, 3 Jun 2002 15:01:52
In Reply to: Aftermarket exhaust bad 4 93 Aero?, Chris M, Mon, 3 Jun 2002 12:51:25
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Perhaps this is what he is thinking of. Normally-aspirated engines tend to have a certain amount of valve overlap to help high-end power, but rely on exhaust back-pressure to stop the fuel/air mixture from going straight out through the exhaust valves at lower RPM. If you put a 3" straight-through system on a normally-aspirated 2.0 car, expect extremely poor performance at low RPM.
Another thing to watch out for is that there are reportedly performance silencers (sorry, mufflers) on the market that assist performance by introducing a scavenging effect (I'm not familiar with US brand names, sorry). These will not work with a turbo and may actually reduce performance.
No, you don't need the rear muffler, if you like the extra noise. It depends on what you're after. The best single component you can change, performance-wise, is the downpipe for a well-engineered performance item. The further back you go, the cooler the exhaust gasses and the less potential for performance improvement.
I have a full JT 3" exhaust system on my '96 Aero and it has certainly helped reduce turbo lag, as well as (subjectively, anyway), helped power at high RPM. When the silencers rust through, I might consider replacing the cat-back part of the system with something quieter now I know the downpipe and cat are the most significant components. Not that it's super-loud anyway.
posted by 80.2.252...
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