the vehicle in question is an 89 sedan. The question is on my exhaust sizing. motor for now is a stock d15b2, swapped to mpfi, light weight crank pulley, light weight flywheel, no other engine modifications, but a CAI. The exhaust ive gotten is a 4-2-1 header and high flow cat. Would running custom fabbed 2.5" exhaust be too much. Would i be going too large and losing too much back pressure? I'm also looking into going with JDM Vtec d15b motor, do i need to reduce my exhaust past the cat to 2.25" or less? any input is appreciated!

 

any ideas? bump

 

2.25" should be fine unless you plan on going forced induction in the future.