bit of confusion on exhausts

[sad_rocc@veedub.com (Dan Smith)]

Well, that makes sense. For more info, the TT exhaust is 2.25", the muffler is 2.5" inlet, dual 3" outlets. (God I hope it doesn't sound like a fartcan) It seems velocity would be the same as in a stock setup, as the sizes aren't changing, just the restrictions, or lack of. Am I correct? And do others agree that backpressure is a myth?

Dan

--- Ryan H <rhock99@epix.net> wrote:
>I can't answer your question about your exhaust, but I can offer my knowledge on back pressure...
>This is a big myth... from what I have read, you don't want ANY backpressure, you want exhaust gas velocity.  The reason people think you need backpressure is simple: If your engine only generates 250 cfm of exhaust gases, and you have a 3.5" exhaust, the exhaust has so much room when it makes it to your 3.5 inch pipe, that it has no need to move further down the pipe, and it creates a sort of wall.  This causes exhaust gas velocities to slow, and interferes with the ability of the exhaust system to "scavenge" exhaust gases from the engine when the exhaust valves are open.  This means the engine has to force exhaust gases out the valves, instead of it being sucked out by the exhaust system, and this is where systems with "too little backpressure" (in truth, exhaust gas velocity) lose their power.
>I guess it would take some experimentation on your part to see what allows your car the maximum exhaust flow rate.
>
>> 
>> From: Dan Smith <sad_rocc@veedub.com>
>> Date: 2002/11/26 Tue PM 01:59:12 EST
>> To: scirocco-l@scirocco.org
>> Subject: bit of confusion on exhausts
>> 
>> I have a stock 1.8l 16v, which hopefully at some point will change. I've been looking into an aluminized TT setup with no resonator and swapping the muffler for a fireball dual tip straight-thru design. I've heard though that you want some backpressure and if your exhaust is too free flowing, then you actually lose power. What exactly is the real deal on this? And would this setup be too free flowing? Suggestions, comments, ect.
>> 
>> Dan
>> 
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