Little about the truck first. '99 -7.3. basic fuel mods- banjo bolts ,regulated return,62+psi spring, new bosch lift pump. Turbo - "stock" garret with "XDP" X-wheel, bellowed up pipes, Riffraff exhaust back pressure valve delete kit. Intake - 6637 mod. exhaust- 3.5" strait pipe stock down pipe. Tranny all stock as far as I know, except for bullydog shift kit. Thats the major stuff. I do have some minor stuff like Riffraff oil and fuel crossover kits, sinister coolant filtration kit installed etc.

So I'm trying to decide on weather I should dump some money on replacing the 3.5" exhaust to a 4" down pipe and either to 5" stacks or 5" strait. (havent decided yet)..... Or, proceed with getting a tuner. (made my mind on the sct x4.) My question is: Will the size of the exhaust (even though its straight piped) have an effect on the performance of the truck with a tuner intaled? Obviously EGT's are my concern. will the 4"-5" stuff flow better than the 3.5" straight pipe?
Opinions , ideas and of course facts always welcome.

 

exhaust will have very little effect on it. 4" is as big as you need, 5" does nothing for performance and will only change the sound.

as far as a tuner the X4 is garbage on a 7.3. not very many tuners will tune for that, so you are limiting your options right away. then you are stuck in one tune till you have 15 minutes of down time to change it. the best option on the market for the 7.3 is a hydra