I'm doing a true dual set up and was wonder what size piping should I get, is 3.5 inches good or do i need more? And does shorties headers fit right to the cats like the factory headers?

 

Well I would think 3.5 duals is a little overkill for the mods you have plus the sound would be a little loud even thought that is proably what you are going for. There would proably be a lot of backfire form the oversized pipes. I am using 2.5 inch and i love the sound. Has a nice idle and a hella loud top end. The factory exhaust is only 2.75 and is single so dual 3inch would be the biggest I would go. also going bigger creates clearance problems. You will also have more money in the duals with shorties since you will need to make custom down pipes to the frame of the car as to where longtubes are perfect for true duals since all you need is straight pipes.

 

Unless you have heads and cam in a stroker or a supercharger, you won't need anything bigger than 2.5" duals.

 

I run dual 3" pipes, with 3" Borla XR-1 shorty mufflers, and that's good for approx. 800 flywheelHP. A friend of mine is running 3.5" duals with 3.5" Borlas, and he's pushing 1,325 flywheelHP.

I'd say 2.5's should be OK

If you are getting "shorties", are they dual-cat, or single-cat? The dual cat shorties will be only the headers, and they will bolt up to the stock Y-pipe, to keep the cats in the stock positions. If they are "single-cat" shorties, they will include a Y-pipe, probably no more than 2.5" branches. You will need to do some fairly extensive work to run "true duals" with shorty headers, and the gain over a simple 3" catback, or even a 3.5" catback will be marginal.

"True duals" work best with long tube headers.