Hello guys, I now have fitted a Supersprint 2.5" (standard diameter but without catalyst) downpipe. The first hole is the same as the standard downpipe with catalyst (no big hole as the SS downpipe to flow the wastegate gases better).
Should I go for a SS downpipe that has 3" and big hole for wastegate gasses????
ric

 

On the off chance that you'd like the question in the title answered the PE T65 and T75 downpipes are named with their diameter in mm. So T65 = 2.5 inch and T75 = 3 inch.

Not having the blanking plate across the turbo exit should make a difference, as should the increased diameter, but since you've already removed the cat I don't know how much that alone restricts the gasses.

Paul