This was taken from Flowmasters website. I have also seen this on other sites as well. I was also told this from the shop that installed my set up.
12. What size exhaust tubing should I use for my street application?
The size of tubing used in an exhaust system is as important as selecting the right muffler. Your tubing diameter choice will affect the sound level and performance characteristics of the muffler, but keep in mind that bigger is not always better. Using tubing that is too large can actually hinder exhaust scavenging by slowing the velocity of exhaust pulses in the tubing. As a rule, most stock street applications (dual exhaust) use 2.00” through
2.25” tubing, and modified street applications will generally use 2.25” or 2.50” tubing. Very rarely will 3.00” tubing be used for street applications.
Thank you for confirming my statement, aside from the "y pipe is the biggest restriction after the factory cats" part, which is true by the way,
A stock hemi or lightly modded hemi only needs a single 3 or dual 2 1/4
People running boost or n2o (or both!) is a different story!
So basically if you got a catback system that did not change your factory y pipe you may as well have gotten a muffler delete or swap and saved the money.
The OEM system is quite well made, aside from the ugly y pipe. All stainless and mandrel bend, what more do you want? (More than a y pipe)
There are several threads on here with photos of the stock y beside the magnaflow y and once you will see the difference you will understand real well!
These guys say lots of things in general. They are not hemi experts. Gm 6 litre 2500 2009 to at least 11 or 12 (trucks i work on) comes with a y so nice it looks like a mf y and 3" mandrel from the manifold to the y into single 4 so for the exhaust shop guy to recommend the same thing for every truck is ridiculous.
