exhaust size??

[WCH_diesel]

hey guys im buying exhaust this week and want to know what size i should go with 4'' or 5'' and the down pipe is it better to have a 3.5 or 4'' ive heard alot of different things but nothing the same,some help please

[colo_dually]

What are your plans as far as power goes?

Staying under 500HP, just a tuner, go with the 4" system.
Plans on going big, or like a loud exhaust, go with the 5" system.

As for DP, I'm trying to find a 4" that mates to the CAT but not having any luck. There is not much of a change between the 3.5" and the 4" DP for EGT's.

[PGreenSVT]

A 4" is fine and sounds great straight piped. A 5" will give you a little lower tone. that is the only difference. A 4" down pipe takes some trial and error fitting to get it so it isn't rattling on something like the up pipe, firewall, etc. on the 05-07. A 4" down pipe takes some BFH fitting on an 03-04 to get it in.

Here is the difference between the oem down pipe and a 4".

[rentstdi]

Is the stock downpipe 3-inch?