I've just replaced my tiny FM intercooler with the full sized one from cxracing. The FM plumbing is all 2" and the intercooler is3".

I'm pushing big boy power levels, 25-28psi, and wonder if I can expect credible improvements with 3" all the way. I assume it'll be slightly cooler with 3", but any other advantages?

 

The smallest diameter from the turbo output to the intake manifold input dictates the bottleneck in air flow.
ie. if your turbo oulet is 2" then going from 2" to 3" wont do anything other than make it harder to route the intercooler plumbing.

If your turbo outlet is X", the intercooler barbs are X" and the intake manifold input is X" then X" is perfect.

If anywhere along the route you need to up-size the plumbing (eg. many intercoolers use 2.5" while the turbo outlet is 2"), you want to keep it at that size from there on and NEVER drop back.

Mine is 2" turbo outlet -> 2"-2.5" Si elbow hose-> 2.5" intercooler barbs -> 2.5"-2.75" Si elbow hose -> 2.75" Skunk2 TB (intake manifold ported accordingly)

 

difference will be minimal if at all. you have to have a huge snail flowing serious air to see a difference

 

Good to know, thanks gentlemen!