24gt24gt

I have a 2004 2500hd with the 8.1 gas engine, The stock muffler has two 3 inch pipes going in and out of it then combining into a 3 1/2 inch pipe. I was thinking of making the 2 3 inch pipes collect into a 4 inch pipe then go through diesel type muffler. How would this be for performance/gas mileage? What if i went to a 5 inch pipe instead?

CCrowell2

It would help a little on flow, only thing that would help performance much is headers and no cats or high flow cats. Good tune will wake that 8.1 up also

xx_ED_xx

iTrader: (17)

I have sound clips of various size pipes etc on an 8.1
Me personally i would just make it dual 3 all the way back

mufflers are cheaper easier to find etc and yes a tune will wake them up

Kerr

I have dual 3" exhaust. into a huge maganaflow.. sound ok.

I do have 4" d max stock cat back at the house.. i might try that at some point.

hog

I think you will find that your stock muffler has 2 pipes in and only 1 open pipe coming out. The one pipe is a dummy.

peace
Hog

oldred95

A 2 into 1 might sound cool on a big block. The flowmaster scavenger Y collectors are supposed to make a big difference in exhaust scavenging. I've got this exact one I was planning on putting on my 95 with a dual 3 inch to single 4 inch exhaust before the engine blew and I decided to go turbo charged.

Flowmaster Scavenger Series Y Collectors Y300400 - SummitRacing.com

tman_2006

I will likely go 4" diamond eye on our 01 8.1L farm truck. Looking into cam and head options now. Has 274K on it all oem but the hypertech tow tune.