At what point do the 2.5" y-pipes become a perf hinderence. Does it Y into a 3" pipe or 3.5"?

 

can't really tell you when it will start huring, but i can tell you that it merges to a 3 inch. I would think the 2 1/2 shouldn't be a problem till you are running heads and cam then i think it might hut you about 10 hp but thats just a guess so take that as a grain of salt.

Justin