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Old 10-20-2020, 05:52 PM   #1
Bowties from Birth
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Join Date: Jan 2008
Location: Chester County PA
Posts: 86
3inch exhaust reduced?

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.

68 K10 Burb aka "da bomb"
72 C10 SWB Highlander
97 30th anniv. Z28 Conv
99 Chevy Crew 454
11 Traverse AWD
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Old 10-22-2020, 08:33 PM   #2
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Location: Beaver Falls, Pa
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Re: 3inch exhaust reduced?

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
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Old 10-25-2020, 09:22 AM   #3
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Location: Binghamton, NY
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Re: 3inch exhaust reduced?

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.
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Old 10-25-2020, 04:59 PM   #4
LS short box
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Re: 3inch exhaust reduced?

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.
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