Auto Racing: running off headers, open pipes, pulse waves

Question
me and my buddy got in an arguement the other day about running the exhaust off the headers.  i thought that the less backpressure there is, the easier the engine can breathe, but my buddy says, that especially on old cars the backpressure actually helps the engine breathe, and that the full exhaust system actually boosts horsepower rather than limiting it. how is this possible and who's right? thank you for your time!

Answer
Dominic-

 Actually, you're both right...sort of.  If you ran right off of the headers you'd lose too much backpressure which would effect low end torque.  But factory exhausts are way too restrictive.  This is, of course, assuming the motor is stock.  As an engine's power level goes up backpressure becomes an enemy.  I once saw a graph of a top fuel funny car where just for fun some guys threw a traditional aftermarket exhaust system on it and it lost close to 1,000hp.  But when you run at 6,000hp regularly, I don't think you'd miss 1,000hp a whole lot.  Aftermarket exhaust systems today are actually a big help...especially compared to older setups and factory systems.  Many mufflers that increase velocity and aid in scavenging are readily available.  So really it's all about finding a balance between flow, backpressure, exhaust pulse waves, and velocity.  On a stock engine an actual exhaust system is best.  On a big power racer, open pipes work best. Hope this helps.

Steve