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Dual 2.5" exhaust?? #1333522
11/10/12 10:05 PM
11/10/12 10:05 PM
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Iowa
76dodgeboy Offline OP
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Is dual 2.5" exhaust to much for a stock 318 with headers and a 4bbl? 84 Chrysler 5th ave. Looking for best exhaust size for optimal fuel economy. Thanks

Re: Dual 2.5" exhaust?? [Re: 76dodgeboy] #1333523
11/10/12 10:35 PM
11/10/12 10:35 PM
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Lethbridge, AB, Canada
dangina Offline
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Quote:

Is dual 2.5" exhaust to much for a stock 318 with headers and a 4bbl? 84 Chrysler 5th ave. Looking for best exhaust size for optimal fuel economy. Thanks




I'd stick with the 2 1/4"

Re: Dual 2.5" exhaust?? [Re: dangina] #1333524
11/10/12 10:49 PM
11/10/12 10:49 PM
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76dodgeboy Offline OP
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For duals? The A body 2.5" kit fits the 5th ave and dippy cars. Guy at exhaust shop said it would be too much but a single 2.5" would be good. Just looking for the cheapest route. Getting the kit and a h-pipe would be around what the shop wants but a shop is custom and welded not clamped. There's also a guy on the dippy forum that only used the right side of the kit and thinks the left side might work for the left and I could do that myself and use an H-pipe but use an elbow to hook the driver side to the passenger side. But again clamped not welded

Re: Dual 2.5" exhaust?? [Re: 76dodgeboy] #1333525
11/11/12 12:14 AM
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I believe any neckdown aft of the collector flange hurts performance/mileage/efficiency and that correct dia/length for pressure wave tuning etc is a function of the pri tubes. I would rather have (4) 1&5/8 pri tubes collected down into a 2&1/2" pipe rather than into a 2&1/4" one


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Re: Dual 2.5" exhaust?? [Re: RapidRobert] #1333526
11/11/12 12:48 AM
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76dodgeboy Offline OP
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Not being built for performance just optimum fuel economy. Having 2.5" duals is larger than a single 3" and he didn't recommend a single 3" either. Less backpressure. I believe my headers have 3" collectors g9040 I believe is the part number for them.

Re: Dual 2.5" exhaust?? [Re: 76dodgeboy] #1333527
11/11/12 12:50 AM
11/11/12 12:50 AM
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76dodgeboy Offline OP
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The performance will already be improved over the stock smog motor manifold also

Re: Dual 2.5" exhaust?? [Re: 76dodgeboy] #1333528
11/11/12 08:40 PM
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For economy I would go with dual 2.25 or a single 2.5 mandrel bend with a straight through muffler.

Re: Dual 2.5" exhaust?? [Re: gch] #1333529
11/11/12 08:56 PM
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76dodgeboy Offline OP
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Exhaust guy was going to use a flowmaster knock off. And run 2.5" single. I found sizing chart on magnaflows site. Says 2.5" duals are fine for 250-350cid and hp was 150-350 for the same. I guess I have till may to get it done but price might go up by than

Re: Dual 2.5" exhaust?? [Re: 76dodgeboy] #1333530
11/11/12 10:48 PM
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Lubbock, TX
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I run a 2.5" system with a Flowmaster (yeah yeah)on my stock 5th with Edelbrock Performer and 1406 carb (on a low compression/stock cam 318). I think with headers on your stock engine, a large single system should be good. Personaly, I wouldn't even run headers on a stock engine, but its your car.


Eric
Re: Dual 2.5" exhaust?? [Re: Erics5th] #1333531
11/11/12 10:53 PM
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76dodgeboy Offline OP
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Its getting a 4bbl when the headers go on and later object itll get an Rv cam and hopefully a 518

Re: Dual 2.5" exhaust?? [Re: 76dodgeboy] #1333532
11/12/12 11:14 PM
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If you after mileage then hp is'nt a concern at all.Headers with a good flowing Y-pipe(flowmaster has some really nice ones)and a straight through muffler will weigh less and flow more than enough in the rpm range you will be in 99% of the time.

Re: Dual 2.5" exhaust?? [Re: gch] #1333533
11/12/12 11:19 PM
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76dodgeboy Offline OP
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The exhaust gay plans to build it from the headers back for less than I can using the dual kit an h-pipe and a 90°

Re: Dual 2.5" exhaust?? [Re: gch] #1333534
11/12/12 11:24 PM
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76dodgeboy Offline OP
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What kind of straight though? I also want it to sound good. I don't plan to "baby" it all the time. He has flowmaster knockoffs. Im kinda surprised there are no exhaust guys on here

Re: Dual 2.5" exhaust?? [Re: gch] #1333535
11/12/12 11:34 PM
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Mopar Muscle did the Stealth Bomber Diplomat build and out a warmed 360 in it with headers and went, I think, 3.5" to the muffler and 3" after to the back.

If I were you I would go 3" single all the way back. If a dual 2.5" will work and its in a kit form then use that, it won't hurt your gas mileage but will improve power. With a cam 4bbl and headers it could use at least a 3" single

Re: Dual 2.5" exhaust?? [Re: 76dodgeboy] #1333536
11/12/12 11:39 PM
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I bet one 3" exhaust will work great there's a guy on the Columbia CL that sells & ships performance X,H & Y pipes cheap as well as muffs $40 & less

Re: Dual 2.5" exhaust?? [Re: BulletBob] #1333537
11/13/12 12:49 AM
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76dodgeboy Offline OP
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Im just leary that 2.5 duals are too much. Plus Im not digging the all clamped together joints. the A-body kits summit/jegs sells fit just have to move the fuel tank to center. Exhaust guy said single 3" was to much for the sickness of the motor. It would make less backpressure and work the motor more.

Re: Dual 2.5" exhaust?? [Re: 76dodgeboy] #1333538
11/13/12 12:53 AM
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76dodgeboy Offline OP
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It would be $310 for me to get the dual kit with h-pipe and 90° to make my own single 2.5". Shop only wants $260-275 from headers back.
If I did duals I want an h-pipe so that puts me at just over what he wants for single 2.5". He also said it wouldn't cost much more for duals.

Re: Dual 2.5" exhaust?? [Re: 76dodgeboy] #1333539
11/13/12 01:28 AM
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The back pressure thing I don't understand, IMO it's a bunch of nonsense, like how 15-20 years ago the common knowledge was that a turbo NEEDED back pressure to work properly which is BS. Back pressure makes an engine work harder, costing efficiency. And really, an engine turning ~2000 rpm at 20% throttle opening doesn't care if you have a single 2.5" or 3" or dual 2.5", you wouldn't have back pressure with any of them since you aren't flowing enough air/exhaust to max any of them out and it would be a wash from a mileage stand point IMO. Where you will notice it is when you do want to play (which you will) and get on it.

BTW, a single 3" pipe has less surface (7.065 sq in) than a dual 2 1/4" (7.95"), but the 3" has less boundary area than a dual 2 1/4" so it's probably a wash and they flow a similar amount of air. Remember, 250 hp Dakota RT's came with a single 3" system from the factory (along with the 98 and later rams, they may have 2 3/4" systems though)

Your exhaust guy may be feeding you a bit of a line about "back pressure" cause a lot of places don't like bending anything bigger than 2.5", go with the 3" single

Re: Dual 2.5" exhaust?? [Re: WO23Coronet] #1333540
11/13/12 03:11 AM
11/13/12 03:11 AM
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I would consider going with a 2 1/2" dual system with 2 1/4" tail pipes to lessen the chance of exhaust drone. Too large a tail pipe can act like a megaphone.

Re: Dual 2.5" exhaust?? [Re: 74RALLYE] #1333541
11/13/12 03:48 AM
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76dodgeboy Offline OP
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I don't mind loud exhaust.

A Dakota Rt has more horsepower than a 1984 318. I don't know much if anything about backpressure. Magna flows site does say 2.5" duals are ok.
The a-body kit comes with turbo mufflers which Im not positive I'll like.
Im sure they have talked about backpressure on powerblock before or one of the car shows. I think Ill do some more research before I spend the cash. I still find it hard to believe there are no exhaust guys on here

Last edited by 76dodgeboy; 11/13/12 03:53 AM.
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