What is the diameter of a B18B1 stock exhaust system?

 

1995 and earlier - 1.854"

1996 and up - 1.745"

I believe this is the correct measurements as i know my old exhaust was 1.75" off my 98 teg.

 

Thanks Paul. Would a header with a 2.5" collector fit the 1.75" cat?

 

Yes it can, but it'd probably worth your time to get a hight flow cat...keep the stock OEM just in case.

 

I have one on the way actually but I was wondering if it was possible to bolt up the header in the mean time just for something to do one night lol

 

The stock size on DC integras is 2" outside diameter, so about 1.75" inside diameter.

Going to a bigger exhaust will not give you more power if your just going to do a cat back, your going to lose hp because you are losing back pressure, which the engine needs to make the hp. The only way your going to make more HP from a cat back, is you need a header and put on a aftermarket intake system on it.