I recently purchased and installed nismo headers, invidia test pipes, ichiba y and an AAM 3" ti single. The headers collect to 2.25" and the invidia test pipes are 2" my mistake the pipes had a minimal description and all the pipes i researched were a minimum of 2.5". My question is, am i significantly reducing flow or am i creating necessary back pressure...? (by the way the y-pipe is 2.5"to3"

 

Yes. The weakest link of the exhaust system is the most restrictive component. The test pipes are a choke point.

 

so basically 2.5 inch test pipes for NA motors, and 3 inch test pipes and everything else that size for FI cars correct? or what about if he were to do 3 inch test pipes and 2.5 inch exhaust would that help?

 

Yeah i figured this was a no go i was just trying to convince myself that it was alright to leave them in. Thanx for the input

 

2" is pretty small for test pipes.

2.25"-2.50" are the best sizes (NA).