you dont need backpressure right? just good for mpg so y do u need it or do u?

 

nobody wants backpressure. thats an old wives tale. "engines need backpressure" is bullshit. engines need exhaust gas speed ....aka velocity. to make power and run properly. free flowing exhaust with proper size pipe is what works.

 

and like runnerdown said its gas velosity so dont think you should go buy a 3" exhaust for you 250whp engine becuase it will decrease back pressure. A 3" on an application like that will slow exhaust velosity. A large pipe will let the exhaust expand and cool down on its way out which will slow velosity.