Im going to be running 10-11 psi on my gsr(stock internals) and I need a downpipe for my custom setup. I am stuck on how big I should make it. I do want a 3 inch exhaust, but I dont know about downpipe and cat. I assume I will want to go with a 3 inch downpipe, but I heard they spike and thats the last thing I want on stock internals. Will 2.5 do the job?? Or should I go with the 3 inch? Thanks for replies...

 

If you go with a 3 inch you will not be able to retain your AC. that may answer your question..

Rob

 

3 Inch you will spike with a Drag manifold because of the way the wastegate is located.

 

dis boy aint gonna have a/c..

 

is it worth it to get a 3" (thermal for instance) exhaust running a 2.5" dp?

 

Yes, it most definately is!

 

My CX doesnt have ac anyway, but I will be using an inlinepro manifold with a tial wastegate. Is it still gonna spike?

 

I found that the WG flange on Drag manifold was not very well matched with the gasket. A little porting on the flange ought to solve the spiking problem.