I was bored and was looking at the specs for buschurs evo package available at medina mit. why did he use a 2.5" dp and go to a 3" exhaust??? why not go with a 3 " dp.....

 

If you do some research youll find that some people think 3" is to large for the stock turbo and slows the gas through the exhaust or may have some other negative effect. IMHO i think 2.75 is optimal buts its the most expensive to produce because its an unusual size. a 2.75 down pip should cost more money then a 3".. which is why 3" are probably pushed on eveyrone so much.

 

oh yea, now i remember seeing a thread on this. No one could agree though. some people thought less restriction after turbo=better spool and some people said 3" was just too big and had - results.

 

no , he did it so it would not bottleneck at the stock cat , they kept the stock cat for emissions or something like that

 

that makes more sense

 

Yes since it's a new car I think officially they can't replace the cat unless it was defective... of course not flowing enough for the engine output could be considered a defect of sorts! Basically you wouldn't want a 3" downpipe feeding a stock cat and then going back to a 3" Cat back. If the stock cat is considered a restriction on a stock exhaust then it likely flows only as good as a 2" pipe at best. I wonder how much CFM a stock cat versus high flow cat versus 2.5" versus 3" pipe looks like with flow coming out of the typical 4G63.

 

youd lose tones of pwr if you used the 3" with the stock cat... ... only with a high flow or test pipe do you want to use 3" or larger...