2.5" is good for a small block up to 400 HP.....
Alot of guys say that 2.5" is too big for a stock motor, and they are right. But, it does sould cool!
One of my friends has 2.5" dual pipes and generic Flowmasters on a stock 305 with log-style manifolds....it actually sounds really good! You would never guess that it is a 305 until you drive it, lol..
I have headers, dual 2.5" pipes, and 40 Series Delta Flow Flowmasters on my truck, dumped before the rear axle. It sounds GOOD, but it gets a bit loud on extended highway trips when i am pulling 3k rpm the whole way....but hey, i'm 19 so loud is good
