2.5 to 3.0 Exhaust

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1971 CY Dodge Dart said:
I’ll be installing a 3” exhaust on my car this Winter. It’s a basically stock 340 but I want to go big when I do my longtubes and it will allow me to grow into the exhaust as I add more power. Right now my exhaust is a mish mash of sizes from less than 2” up to 2 1/2”.
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My set up works great for me, but maybe not for others. There are a lot of variables. 2.5" collectors with 2.5" pipe welded to the 2.5" flange (at the proper angle) into duel Walker Turbos (not sure why no one ever mentions them) with the outlets before the rear tires (only one bend after the headers) to reduce back pressure. The bends and lengths are all the same on both sides. The headers tubes should all be the same lengths also (a good set). I agree with others here, stick with the 2.5" and you can still grow on your HP if needed.
 
The lower the compression ratio, the bigger the header primary pipe, collector and exhaust needs to be. Higher compression ratios need less primary header tube diameter. Expansion ratio is real.
 
I have hooker competition headers, 3" collectors. I have a custom bent exhaust, over the axle, H pipe, 2.5" with "race" mufflers, welded seams. Mild cam. Stock compression. Idle sound great. A louder than stock, but not enough to piss off the neighbors. When i "light em up", the car guy neighbors wonder if i have exhaust dumps. Loud as hell. There is a bend in the one pipe over the axle im not impressed with but flow seems equal on cold days. with the H pipe im not worried. Im happy with the exhaust. Seems better than the 3" straight pipes with a turn down and mufflers i had on there.
 
Swinger 340 said:
My set up works great for me, but maybe not for others. There are a lot of variables. 2.5" collectors with 2.5" pipe welded to the 2.5" flange (at the proper angle) into duel Walker Turbos (not sure why no one ever mentions them) with the outlets before the rear tires (only one bend after the headers) to reduce back pressure. The bends and lengths are all the same on both sides. The headers tubes should all be the same lengths also (a good set). I agree with others here, stick with the 2.5" and you can still grow on your HP if needed.
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Thanks. I'm thinking now 2.5" exhaust may be enough for me. I plan on running Doug's headers and they come with a 3" collector that tapers down to 2.5" I believe.
 
1971 CY Dodge Dart said:
Thanks. I'm thinking now 2.5" exhaust may be enough for me. I plan on running Doug's headers and they come with a 3" collector that tapers down to 2.5" I believe.
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The collector seldom necks down. The “Reducer” bolts to the collector and often reduces in size. Would this be the case?
 
1971 CY Dodge Dart said:
Yes that’s exactly it.

Doug's Headers D453 Doug's Headers | Summit Racing
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1971 CY Dodge Dart said:
I’ll be installing a 3” exhaust - It’s a basically stock 340 but I want to go big when I do my longtubes and it will allow me to grow into the exhaust as I add more power.
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Before you purchase anything, what is the power level your after? 1-5/8 header tubes efficiently work very well to a certain level. Most times, IMO, a 3 inch exhaust pipe after a 1-5/8 tube header is what I see as a miss match. I’m not saying it doesn’t work but in most cases when power goes up and starts to become a powerful engine, a larger header does better. Most times, the next size up header is a winner in power from start to finish.

Not knowing what you have in mind, my mind see’s a 3 inch exhaust connected to at least a 1-3/4 header.
 
A 2-1/2 inch muffler, chambered or turbo, is good until approximately 450 hp, (give and take a little here on actual design and manufacturing) the 3 inch should carry another 100hp. The straight through mufflers that you can see unobstructed to the other side will carry a good bit more…. (And sound louder…. LOL)

The 1-5/8 header should be upgraded (for sure) on power levels north of 450. Or a straight through muffler should be used to allow the header to work at its best. It gets a bit dicey to make a call here on the internet without, 1; Knowing the build and purpose and 2; Not having a dyno to work with. This leaves you with the track, so enjoy that! I’m sure that’s going to be a lot of fun.
 
When I bought my 69 Barracuda a few years ago it had new hooker headers and 3 inch exhaust. Probably one of the worst fitting exhausts ever. Had the cheap around the steering linkage headers, smashed flat on the driver side. Header collectors dragged the ground on a mild bump. 3 inch exhaust was just too big. Couldn’t keep it away from brake lines. I took it all off & trashed it. Went back stock. Low compression 360, so didn’t really matter.

Just an opinion…..
 
Except for Mike's #36 post, nobody has mentioned fit. It's hard enough getting by trans crossmember, shocks, gas tank, frame trails, etc. with 2-1/2 without rattles. You'll never feel the difference with 3" behind a stock 360. Then there's the guys who do it mostly for bragging rights.

Another thing, I always consider weight when changing things and once calculated 12 feet of 2-1/2 vs. 3 and it was significant.
 
Mopar44134 said:
I have hooker competition headers, 3" collectors. I have a custom bent exhaust, over the axle, H pipe, 2.5" with "race" mufflers, welded seams. Mild cam. Stock compression. Idle sound great. A louder than stock, but not enough to piss off the neighbors. When i "light em up", the car guy neighbors wonder if i have exhaust dumps. Loud as hell. There is a bend in the one pipe over the axle im not impressed with but flow seems equal on cold days. with the H pipe im not worried. Im happy with the exhaust. Seems better than the 3" straight pipes with a turn down and mufflers i had on there.
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turn downs before axle equals increased interior noise vs exhaust to rear bumper.

3” full exhaust over the axle and past stock gas tank is tough to pull off on an A-body. Not much room between leaf springs and gas tank. It just opens up another set of issues. Issues = increased skills or money or both. How much to you have of each to give?

a full TTI has true mandrel bent exhaust. So the mufflers shop 3” will neck down to 2 1/2” size when it bends over axles.
 
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CluelessMopar said:
Yeah I probably should have specified that, my apologies!

I have TTI headers with a 3 inch collector. I was also thinking about going the X-pipe route but from what I've heard in videos it's not as "muscle car" sounding, a bit more modern. I'm hopefully trying to achieve a loader, deeper exhaust sound without sacrificing whatever performance I currently have.
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Gibson Performance Mufflers
Just change to these MWA mufflers for the sound you're looking for with no loss in power. Worked for me. 2.5" exhaust. Changed from a sporty kind of sound with strait-through Magnaflow kind of muffler to the muscle car tone I was looking for with MWAs.
 
I have a 69 B'cuda w/ a stroker low deck BB. My buddy is a TTI dealer and runs a perf shop. We fabbed a 3" x-pipe from the headers to Flowmaster 50 series mufflers on to TTI 3" tailpipes. It's all tucked up nice and those tailpipes fit perfectly. I have never had any of the exhaust scape the ground. Done right it's pretty easy to fit 3" on an A-body without issue.
 
Im going 3in on my 70 Dart. Dont think 3in will provide much more hp unless you have a beast of an engine. I wanted bragging rights.
 
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