Just wondering if diameter matters as much if you're running wastegate dumps. Is 2.5 big enough or should you still get 3". This is for a built motor w/ a greddy kit on it. I've been hearing different things and wanted to get opinions. Thanks

 

i have been testing our 2.5" exhaust for the last week now and running it on my car. ofcourse before that i was running the 3" system. i also have w/g our w/g dumps on there too. this is a great comparison, because both the exhaust designs are nearly identical.
i have had a noticeable gain in part throttle responce with the smaller exhaust, but as i get further into it, it seems to hold back a little. not sure if i am just trippin out or anything, as i havn't dynoed them against eachother on my car, but there does seem to be a bit more throttle responce and bottom end grunt with the 2.5". now to answer your question, i can't wait to get my 3" system back on. i highly recommend anyone over 500rwhp to go with the 3" dual set up. and the 2.5" set up for under 500rwhp.
true, once the w/g dumps open up, you effectively increase exhaust effeicientcy and the difference would be hard to tell at the point, but in the driveability areas, i do notice a difference.

 

Thanks for the imput Scott