i don't see a general exhaust forum on here which is wierd but anyway you can move this post wherever

i have a 2000 civic hatch
i plan on swapping a b18c itr with the jdm 4-1 headermy question is should i run a 2.5 test pipe first and then the 60mm cat back
or should i run the 60mm right after the header?

i plan on keeping the motor stock so what will happen if i run the 60mm right after the header? will i lose low end or top end? also what does this have to do with back pressure

 

you do realize 60 mm is smaller than 2.5", right?

 

yes i was under the assumption that you usually go from 2.5 all the way to the test pipe then 60mm after that

 

60mm exhaust is plenty large enough for the power typically produced by an ITR engine... it will make no difference when you transition from 2.5" at the header collector to the cat-back exhaust system... you will not lose any mid-range power depending on when you neck down the exhaust system. It is likely the smoothest transition is created when you use a 2.5" doughnut gasket and flange welded to the header end of a 60mm straight through design high flow cat or test pipe... which bolts to the 60mm cat-back. A very slight expansion of the test pipe at the header end allows the 2.5" flange to be directly welded to it and the internal transition is clean.

 

i can eather put a 2.5 test pipe after the header and then the 60mm cat back or just put a 60mm exhaust right after the header (no test pipe)