Does it make a big difference? I drive a 90 GTU, soon to have apexi n1 duals.

 

I'm sure a header would help. Especially w/ a lot of other mods.

Just be careful not to open the exhaust up too much or you will lose power. :thumbs-up:

 

A down pipe on a NA replaces 1 or 2 cats... so yes it will be an improvement, without the port/combustion noise associated with a header.

 

sorry I had a brain fart there i meant to type mid-pipe. So yeah

 

Ya a midpipe should help more since it replaces the main cat(as long as the precats aren't in too bad of shape. But I suggest you replace all of your cats with 2.5" piping. That with the N1s should make a nice improvement, especially if the cats are 12+ years old.