I have read alot on this and for the 7.3, the 4" straight pipe seems popular with alot of people. If you want a muffler, use 4" with a Magnaflo or equivelant muffler.
What are you wanting to do, race it, just add power for the family RV or what?
I'm going to use 4" TB, no cat and a magnaflow muffler on my 6.0 when i get some money from momma!
