3inch exhaust reduced?

[CARZ1968]

My 99 c2500 came with 3inch exhaust to the muffler then it reduced to a single 3 inch exhaust. would switching to a dual 3inch outlet with dual 3 inch turndowns give me the best gas mileage/ performance? Should I add reduced turn downs (2.5 inch) instead of the 3"s? Looking to add a cold air kit, performance mass air flow and a program in the future.

[HAULIN' IT]

The short answer would be: It would only help if the single 3" muffler guts/tail pipe are the restriction. If they aren't, you gain nothing.
Spending some time figuring/measuring the inside tubes & opening inside the muffler can be REAL eye opening! Quite often, the manufactures (even BIG well known companies) do all sorts of "cheats" where they use say, a 2 1/2" core in a whole group of mufflers & change just the ends that you see/attach to the pipes...not a problem for a guy with 2 1/4" exhaust or even 2 1/2", but if the engine really needs a 3" & the muffler has a 2 1/2" core area...pipes mean nothing at this point.
You would have to have a pretty nasty engine to need dual 3" exhaust. Also if you do, the words "gas mileage" wouldn't be something you would type very often. I guess I'll leave it at that. Lorne

[b454rat]

I had a similar truck like urs, had the dual 3" into the mufflers. Actually it had dual flow's on it, but i did true duals with i think 2 1/2" into the muffler, then dual 3" out the back. I don't think I gained anything, other than a good sounding exhaust.

[LS short box]

I like to run 3" from the headers to a 3" muffler inlet. Then 2.5" tail pipes if room is limited. If you have the room I'd go 3" all the way.
I would go with an aftermarket mandrel kit or build it out of mandrel bend pieces. Muffler shop tubing benders really squish 3" tubing when they bend it.