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I was watching some hot rodding show the other day and they were talking about small hp gain mods. They talked about all of the basic stuff that I will generalize as the engine's ability to breathe. Now, if you think about the way turbo works, it is forced induction - breathe in. With all of the components of exhaust, you are trying to improve the engine's ability to breathe out.

Now, my question is this. Why isn't viable to help "force" the breathing out process. I mean most "exhaust" mods deal with improving airflow, through better air paths, larger pipes, etc. But, because of the neccessary setup for legal cars, you have to deal with mufflers and cat converters, etc and that puts a natural limit to what you can do. But why can't you setup something that creates negative pressure in back end, essentially sucking the air into the exhaust system and spitting it out? Wouldn't that go beyond all of the exhaust mods most people currently use? Anyway, just a crazy thought...

 
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thats y turbo cars dun have headers..it has a downpipe then a straight sysytem that leads out to the muffler. most ppl that mod there turbo's have a 2.5 dp and a 3' cat but not everyone uses cat ..i mean if u know a mech he can take care of theat for u during inspections. your dun want to use a 3'dp witha 3' cat unless u are runnin at least 400hp or else u will be losing power...

 
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cause then you wouldn't have any backpressure, even worse negative back pressure, and your torque goes out the window. Can't be compared to forced induction where the more air you shove in the bigger the bang.

 
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ok... I see what you mean. I guess I didn't think it all the way through.

 
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he basically said it: any horsepower you'd gain would be cancelled out by torque loss.. and trust me, you want torque- that's the only thing i miss with this civic...