Stock exhaust vs. 4"

[ereed969]

I just did the 6637 intake. Was pretty impressed with the difference. My question is how much difference is there in a aftermarket exhaust vs. a stock exhaust with that is straight piped. Also I was think of doing a 3" downpipe. So I went and looked under the truck to see how hard it would be and it looks like it has already been done. It looks like a 3" all the way to where the cat used to be. Is the stock ones bent cause this has no bends in it and it looks like the firewall has had a BFH to it. Thanks.

[marine5811]

It's an aftermarket downpipe if it's at all round. The stock one is flat and atrocious. If your stock exhaust has been straight piped you're looking pretty good. Going up to 4" would let the exhaust breathe a little more, but the main flow problems are the cat and muffler, which you don't have, so you're money could probably go some other places first, I would say.

[erics diesel]

if the dp is round all the way from the turbo to the cat it has been replaced

[ereed969]

Hell Yea. I was thinking gauges and a chip.

[ol_Blue97]

you wont see mush gain from 4" exhaust with a stock truck engine wise.. but an aftermarket down pipe is a MUST!!

[jjones96]

Originally Posted by ol_Blue97

you wont see mush gain from 4" exhaust with a stock truck engine wise.. but an aftermarket down pipe is a MUST!!

Yes. But bigger exhaust does sound nice. Especially with a down pipe.
And when i did my dp and exhaust my egt's went down quite a bit

[ol_Blue97]

very true... it does sound better, but no real HP gain/ egt drop with straight pipes 3.5" over 4" on stock engine... no the DP is a whole new story like said.

HP gain, drop in EGTs and just lets it breathe