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Re: Dual 2.5" exhaust??
[Re: WO23Coronet]
#1333544
11/13/12 08:10 AM
11/13/12 08:10 AM
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Joined: May 2012
Posts: 100
Tennessee
meep_meep
member
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member
Joined: May 2012
Posts: 100
Tennessee
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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.. 
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Re: Dual 2.5" exhaust??
[Re: WO23Coronet]
#1333546
11/13/12 01:41 PM
11/13/12 01:41 PM
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Joined: Apr 2005
Posts: 15,134
Kelowna, B.C. Canada
DPelletier
I Live Here
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I Live Here
Joined: Apr 2005
Posts: 15,134
Kelowna, B.C. Canada
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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
1970 Super Bee 440 Six Pack
1974 'Cuda
2008 Ram 3500 Diesel
2006 Ram 3500 Diesel
2004.5 Ram 2500 Diesel
2003 Ram 3500 Diesel
2006 Durango Limited
[url] http://1970superbee.piczo.com [/url]
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Re: Dual 2.5" exhaust??
[Re: WO23Coronet]
#1333547
11/13/12 04:22 PM
11/13/12 04:22 PM
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Joined: Aug 2006
Posts: 8,064
Iowa
76dodgeboy
OP
master
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OP
master
Joined: Aug 2006
Posts: 8,064
Iowa
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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
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Re: Dual 2.5" exhaust??
[Re: 76dodgeboy]
#1333548
11/13/12 04:50 PM
11/13/12 04:50 PM
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Joined: Jan 2008
Posts: 4,254
Canada
WO23Coronet
master
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master
Joined: Jan 2008
Posts: 4,254
Canada
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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
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Re: Dual 2.5" exhaust??
[Re: 76dodgeboy]
#1333550
11/13/12 07:15 PM
11/13/12 07:15 PM
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Joined: Jan 2003
Posts: 12,043
State of Confusion
hp383
Just a normal tag again
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Just a normal tag again
Joined: Jan 2003
Posts: 12,043
State of Confusion
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My 92 Dak with the Magnum 5.2 has a single 2.5 IIRC.
Join the Penguin Liberation Front!!
Stop the Hippo Occupation!
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Re: Dual 2.5" exhaust??
[Re: Winchester 73]
#1333551
11/14/12 12:49 AM
11/14/12 12:49 AM
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Joined: Oct 2005
Posts: 6,048
Back home in PA
BulletBob
master
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master
Joined: Oct 2005
Posts: 6,048
Back home in PA
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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
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