I have the super comp shorty headers with the y-pipe im going to put the muffler right after that(Delta flow 40 series). but im not sure if i should run a 3 in. pipe to the back then split for the two pipes or run 2.5 in. side by side to the back any suggestions.

 

Single pipe would be easier to route and less expensive. The difference in flow would be minimal assuming this isn't some high-reving, firebreathing beast.

 

The00night....I will assume the headers have a 2.5" collector and the Y-pipe is 2.5" as well. So to keep the velocity up you need to figure the cubic inch diameter of the pipes in question. A 2.5" pipe has a cubic inch diameter of 4.90 times 2 pipes is 9.80 cubic inches. A 3" pipe has 7.06 CI dia so it is considerbly less than the 2 2.5" pipes. A 3.5" pipe has 9.62 CI dia and would be the best for velocity and less restrtictive for a 2.5" to 3.5" back out to 2.5" system.

I must agree with five7kid also. If it is a run of the mill the difference will be minimal.

 

The engine is a very strong 355 how strong not sure yet. 10.5-1 compression if that helps any. its the 3 in. y-pipe and colector that is on my particular ones.