I read this write-up on AF a long time ago about two measured types of pressure in your exhaust: backpressure and another type, like qpressure or some ****, I cant remember... anyway, the article said that lack of backpressure is good but the other pressure is needed to maintain mid-range power. Can anyone clarify this or have I lost my mind completely? Thanks in advance,

- Jake

 

the only thing I can think of is you don't want backpressure-but you do want to limit ex. diameter to keep the exhaust velocity up, and help that good olde scavengin effect.

 

for NA or boost?

 

Backpressure is a myth, no car needs backpressure.

The hp/torque tradeoff relates to exhaust gas velocity ie torque
vs total volume the exhaust can flow ie HP.

With a tiny exhaust you are maximizing torque because the air flows out super fast, but gets clogged up in the higher rpm limiting hp. With a exhaust that is too big the air is forced to exit slowly hurting the "low end torque" but when high rpm arrive the exhaust has plenty to room to leave. This is the classic tradeoff between torque/hp, this is also a tradeoff in intake manifolds and heads themselves.

 

Arg, this is driving me insane. Yeah I know backpressure is a huge myth. I want to know what the name of the other pressure measurement is. Oh well, thanks for your help everyone.