Everything including the X-pipe, muffler in/out, and piping is cheaper when you go 2.5 inch instead of 3 inch. I have several mods but nothing major, is it worth it for me to spend the extra $ on 3 inch piping over 2.5 inch piping? If so what kind of differences are we talking about?

 

2.5 inch duals should be good to 500rwhp or more. I have 2.5s and my ground clearance sucks and i dont even have an x-pipe. But they do sound really awsome at idle and wot. Pics are in sig.

 

3" for true duals would be a waste of money. I remember doing the calculations to see how big I would want to go if I went with true duals, and it was much smaller than I had anticipated. The reason being is obvious--We put 3" on our traditional cat-back's right? That is a cross sectional area of 7.06 sq.in for the exhaust of all 8 cylinders to exit and is plenty unless you've got a motor that breathes heavier than my emphasima suffering grandma, in which case some guys seem to go with 3.5"-4" which is probably still over kill.
If you're running true duals, and you have 3" pipe, that cross sectional area is 7.06sq.in per 4 cylinders. So you doubled it, and while it is good to have a non-restrictive exhaust, it is also important to keep the exhaust velocities reasonable. The bigger the cross-sectional area, the lower the exhaust velocity.
Sorry if you didn't want the long explanation, but the final answer is:
stick with the 2.5inch piping and save yourself some money.
Also, comparing cross-sectional areas, 2.5" duals is equivalent to 3.5" single exhaust, so you still will have plenty of flow even for a big head port job.

 

I agree with both the guys above, go with the 2.3". 3" would just be overkill.

 

not just overkill...it will kill your torque!

 

I just got done with my new exhaust.... JetHot longtubes, H- Pipe, 2.5" True duals, and bullet's right before Tail-Pipes (Full Lenght) Sounds Awsome,and is louder, and more refined than when a had my cut-out open on my cat-back system. Best I've heard & even my Mom said it sounds "Vicious" !

 

there is a pretty good article in the may issue of popular hot rodding (pg 56). it is rather in depth, and touches on everything from the primaries to the tailpipe. just some more research for you...