I am building an H23 VTEC, and I have the exhaust for my H23 layin in the garage. I bought a header for a 97 H22; I understand it will be a different length, but roughly how much shorter/longer will this combo be? How am I going to have to mod my H23 exhaust to fit?

This is all assuming I start at the cat....i.e.-will I have to run an extension pipe from the cat to the flexpipe, or cut some out from after the cat? If so, how much?

 

Ever thought about having an exhaust shop make you a test pipe? That could make things a lot easier on you.

 

A 97 Header will be about 6 inches shorter than the 4th gen H22a cat location. yes you need a test pipe to make up the gap personally I'd mod the header to get a 2.5" collector and add the length.