Posted By: 76dodgeboy
Dual 2.5" exhaust?? - 11/11/12 02:05 AM
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
Dual 2.5" exhaust??
Posted By: dangina
Re: Dual 2.5" exhaust?? - 11/11/12 02:35 AM
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"
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/11/12 02:49 AM
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 
Posted By: RapidRobert
Re: Dual 2.5" exhaust?? - 11/11/12 04:14 AM
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 
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/11/12 04:48 AM
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.
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/11/12 04:50 AM
The performance will already be improved over the stock smog motor manifold also
Posted By: gch
Re: Dual 2.5" exhaust?? - 11/12/12 12:40 AM
For economy I would go with dual 2.25 or a single 2.5 mandrel bend with a straight through muffler.
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/12/12 12:56 AM
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
Posted By: Erics5th
Re: Dual 2.5" exhaust?? - 11/12/12 02:48 AM
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.
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/12/12 02:53 AM
Its getting a 4bbl when the headers go on and later object itll get an Rv cam and hopefully a 518
Posted By: gch
Re: Dual 2.5" exhaust?? - 11/13/12 03:14 AM
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.
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/13/12 03:19 AM
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°
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/13/12 03:24 AM
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
Posted By: WO23Coronet
Re: Dual 2.5" exhaust?? - 11/13/12 03:34 AM
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
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
Posted By: BulletBob
Re: Dual 2.5" exhaust?? - 11/13/12 03:39 AM
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
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/13/12 04:49 AM
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.
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/13/12 04:53 AM
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.
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.
Posted By: WO23Coronet
Re: Dual 2.5" exhaust?? - 11/13/12 05:28 AM
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
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
Posted By: 74RALLYE
Re: Dual 2.5" exhaust?? - 11/13/12 07:11 AM
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.
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/13/12 07:48 AM
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
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
Posted By: Winchester 73
Re: Dual 2.5" exhaust?? - 11/13/12 08:38 AM
bigger pipe has always equalled better gas milage in the stuff ive played with.i had a slant six valiant four door with a custom 2.5 inch pipe going into a flowmaster knockoff and ending infront of the rear end.it got way better gas milage after i put that on.sold the car to a buddy and he ran more 2.5 inch pipe to the back bumper and said the loss of gas milage was noticeable.
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/13/12 08:52 AM
Either way I go its will flow way better than Stock
Posted By: meep_meep
Re: Dual 2.5" exhaust?? - 11/13/12 12:10 PM
Quote:
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
+1....the back pressure thing is nothing but a bunch of malarkey..
A engine is basically a air pump, just like a vacuum cleaner...anyone that thinks a engine will perform better with "back pressure" needs to go out to their garage/shop...turn on their shop vac, then partially block off the exhaust port on the vacuum with their hand, then see how much better it sucks crap off the floor with your hand over the exhaust..
Posted By: WO23Coronet
Re: Dual 2.5" exhaust?? - 11/13/12 12:31 PM
With a cam, 4bbl and headers I bet your 318 won't be far off what a stock Dakota R/T puts out
Posted By: DPelletier
Re: Dual 2.5" exhaust?? - 11/13/12 05:41 PM
dual 2.5" system is good for up to 500hp (mandrel bent with good mufflers) with zero HP loss. Backpressure is a bad thing so while it's overkill for the OP, it doesn't hurt anything either.
Dave
Dave
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/13/12 08:22 PM
Quote:
With a cam, 4bbl and headers I bet your 318 won't be far off what a stock Dakota R/T puts out
Considering it will be an rv cam I doubt the combo is close. Low compression smog motor. Also the Dakota Rt has a 360 does it not? And higher comp in stock form. I doubt Ill gain much hp. Im also not after more hp its economy Im after
Posted By: WO23Coronet
Re: Dual 2.5" exhaust?? - 11/13/12 08:50 PM
My brother had an 89 318, with an MP 430/450 260/268 cam (little better than RV) crappy manifolds,cast intake w/a thermoquad, 2" dual exhaust, 2.94 gears in an 83 Cordoba and it would take a Durango RT in a street race. Yes the Durango was probably 800-1000 lbs heavier, but had the advantage of 3.92 gears and computer control, the only tuning the Cordoba got was turning the distributor till it sounded good and setting the idle mixture.
You'll have headers as an added bonus, and I agree, you won't put out what an 360 Magnum will but you'll be suprised. Let us know what you go with, it'll be interesting
You'll have headers as an added bonus, and I agree, you won't put out what an 360 Magnum will but you'll be suprised. Let us know what you go with, it'll be interesting
Posted By: 76dodgeboy
Re: Dual 2.5" exhaust?? - 11/13/12 10:50 PM
Im really considering the dual kit and an h-pipe or x-pipe. It would redeem my last 5th ave effort of having dual glasspacks dump at the rear and not sounding anything like Id hoped and it was All stock other than leanburn delete. But we got a discount cause we took 3 vehicles that day. He ransom himself out of business
Posted By: hp383
Re: Dual 2.5" exhaust?? - 11/13/12 11:15 PM
My 92 Dak with the Magnum 5.2 has a single 2.5 IIRC.
Posted By: BulletBob
Re: Dual 2.5" exhaust?? - 11/14/12 04:49 AM
Quote:
bigger pipe has always equalled better gas milage in the stuff ive played with.i had a slant six valiant four door with a custom 2.5 inch pipe going into a flowmaster knockoff and ending infront of the rear end.it got way better gas milage after i put that on.sold the car to a buddy and he ran more 2.5 inch pipe to the back bumper and said the loss of gas milage was noticeable.
I've had good results with a single 3" remember backpressure is like a dirty air filter I'd use a small tube header to keep torque up