3.5 or 4 inch single exhaust

[DRAGGIN95]

Hello, I would like to run an idea I have by you guys and get your opinions, I have a 95 crew cab stepside truck that is bagged, I have limited space for exhaust. First off the truck has a TSP 408 with a 4L80E and Schoenfeld headers, I do not want to loose any bottom end torque by running to large of an exhaust, I was already planning to run 2.5 pipe from the headers on both sides back to a Y, but I do not think that one 3 inch pipe is enough for the size of the engine so I would like to merge the 2 pipes together in to either a 3.5 or 4 inch single pipe, with one good flowing muffler, probably either a Race Flowmaster 1 chamber or a race Spintech, also there are no cats on my truck, which do you guys think would be better 3.5 or 4 inch single pipe? Thanks!

[canada4g63]

if your running a 408 i don't see a 3.5 to 4.0 inch making a huge difference. Also what do you mean run a 2.5 pipe to the y pipe? are you talking about were the y pipe meets?

[DRAGGIN95]

I am going to run 2.5 inch pipe from the header collector on each side to the y where they will merge and go in to either 3.5 or 4 inch pipe.

[DRAGGIN95]

Anybody else have any thoughts about doing the exhaust this way, or is anyone on here running a single 3.5 or 4 inch pipe and if so what is your experience?

[Duct_tape123]

http://www.popularhotrodding.com/eng...re/0505em_exh/
This is a great article that explains a lot about exhaust and its effect on an engine.
3.5" pipe flows around 1106 CFM
4" pipe flows around 1445 CFM
After the flow of the piping reaches 2.2 CFM per HP there isn't much gain.
Say your motor makes 600hp at the crank. 600 x 2.2 = 1320CFM
So the 3.5 may be a little small, but say you only make 600hp at 5000 rpm. How often do you drive at 5000+ rpm?

[stngh8r]

Easy option, get a 4"CB for a diesel app in your year model. 4" mandrel and prebent. Plus a straight thru muffler. FYI- I don't think the Spintech flows very well.