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post #1 of 22 (permalink) Old 05-01-2008, 07:41 AM Thread Starter
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Single vs. Dual Exhaust Question

But not the normal one.

If the area measurement between a dual exhaust and a single exhaust is the same, will one make more power and/or torque than the other?

For example:
Dual 2.5" = 9.82 sq in total area
Single 3.5" = 9.89 sq in total area

Which one will provide the best horsepower and which will provide the best low end torque?

And why!!

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post #2 of 22 (permalink) Old 05-01-2008, 07:56 AM
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With exhaust you are dealing with volume. A 3.5" single exhaust is going to kill your low end as it flows at a higher rate than the 2.5" exhaust does.
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post #3 of 22 (permalink) Old 05-01-2008, 02:26 PM
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with respect to volume, i'm afraid you're incorrect LOLA

V=Area*Length

the volume of a pipe is the cross-sectional area multiplied by the length.....so the length of the pipe will still be pretty much the same to the rear bumper of the car.....and as 94DD pointed out, the cross-sectional area of a dual-2.5 vs a single 3.5 is pretty much identical

as far as the original question, i personally havent seen any tests between such setups.....but if you want low end torque in an mn12, you'd have to use relatively smaller pipes (<2.5") to increase the exhaust flow velocity out of the cylinder.....an X-pipe is also said to help increase some scavenging to promote better torque output overall
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post #4 of 22 (permalink) Old 05-01-2008, 02:39 PM
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I suspect that the power and torque curves would be so close that there would not be a measurable difference. I think the difference in sound however would be drastic, and a single 3.5 would probably sound like crap compared to dual 2.5s.

Oh yeah, also the car with the single 3.5" exhaust would be slightly faster because it would weigh slightly less because there is only one exhaust pipe running to the back instead of 2.

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post #5 of 22 (permalink) Old 05-02-2008, 12:49 AM
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Originally Posted by guitar maestro View Post
with respect to volume, i'm afraid you're incorrect LOLA

V=Area*Length

the volume of a pipe is the cross-sectional area multiplied by the length.....so the length of the pipe will still be pretty much the same to the rear bumper of the car.....and as 94DD pointed out, the cross-sectional area of a dual-2.5 vs a single 3.5 is pretty much identical

as far as the original question, i personally havent seen any tests between such setups.....but if you want low end torque in an mn12, you'd have to use relatively smaller pipes (<2.5") to increase the exhaust flow velocity out of the cylinder.....an X-pipe is also said to help increase some scavenging to promote better torque output overall
Hmm... But wouldn't a dual have twice the length when added together because there are 2 pipes?

I run a single 3" on mine and the pipe is overall shorter because the pipe can be bent less severely since there is only one pipe. I'm sure the difference is minuscule at best, but just putting that out there.
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post #6 of 22 (permalink) Old 05-02-2008, 05:48 AM
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think about it water being pushed thru a big pipe will run slower than the same amount of water being forced thru a smaller pipe. Just like pinching down a water hose to get the water to shoot out quicker. With exhaust uyou want good vaccum the bigger the pipe the slower the gases flow=poor vaccum. also when gases cool they become more dense and slow down due to loss of heat

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post #7 of 22 (permalink) Old 05-02-2008, 08:12 AM Thread Starter
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Quote:
Originally Posted by twin turbo 281 View Post
think about it water being pushed thru a big pipe will run slower than the same amount of water being forced thru a smaller pipe. Just like pinching down a water hose to get the water to shoot out quicker. With exhaust you want good vacuum the bigger the pipe the slower the gases flow=poor vacuum. also when gases cool they become more dense and slow down due to loss of heat
That's the thing though, it's not the "same amount of water."

With dual 2.5" exhausts even though it is smaller, it is only passing half the volume of exhaust. (We're talking true duals here, no crossovers, x pipes, etc.) The other 2.5" pipe is handling the rest.

With the single 3.5" exhaust it is passing the exact same amount of volume as the dual 2.5" with the exact same effective area.

I lean toward the single 3.5" giving slightly more power because all the exhaust pulse waves are "inline" (assuming equal length headers), whereas in the duals, the pulses are not sequential due to the firing order.

But just my babblings, and why I asked this question.

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post #8 of 22 (permalink) Old 05-02-2008, 09:00 AM
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Quote:
Originally Posted by sCrEaMiN BiRd View Post
I run a single 3" on mine and the pipe is overall shorter because the pipe can be bent less severely since there is only one pipe. I'm sure the difference is minuscule at best, but just putting that out there.
Same for me. 3" was the choice for my car by a very good exhuast guy. He thought it better than duals because the single pipe is straighter. I am very happy with the results and it has lots of low end torque and a very flat torque curve. 276 lb-ft max at the wheels.

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post #9 of 22 (permalink) Old 05-02-2008, 09:22 AM
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Quote:
Originally Posted by 94 Daily Driven 4.6L View Post
I lean toward the single 3.5" giving slightly more power because all the exhaust pulse waves are "inline" (assuming equal length headers), whereas in the duals, the pulses are not sequential due to the firing order.

But just my babblings, and why I asked this question.
That sounds about right to me, considering the reason for the X or H pipe is to balance the pulses, and an X or H pipe makes slightly more power than true duals without it. Still though, the sound of a single 3.5 compared to dual 2.5 would be enough to make me not want it. I've heard a single 3.5 on an LS1 firebird, and it sounded awful.

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post #10 of 22 (permalink) Old 05-02-2008, 09:31 AM
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I used a 2-1 resonator vs. an x or h pipe. It does have a different sound than an F-body or Stang. Personally, I like it better. My stock LS1 TA has a gurgley sound similar to the Stang. The Bird has more of a low rumble.

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post #11 of 22 (permalink) Old 05-02-2008, 10:27 AM
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Just shooting from hip here, but I'd say the 3.5 single will outflow two 2.5, in equal setups (same length, same bends). My reasoning is that line loss in fluid flows result from the fluid shear present where the fluid is moving against the pipe. Does that make sense? I'm not sure if that's phrased well. Anyway, while both a single 3.5 and dual 2.5's have the same cross sectional area, the total perimeter of the 3.5 is about 11", as compared to 15" for the duals. There's more wall for the fluid flow (exhaust in this case) to rub against, more fluid shear. That's my thought anyway, but I'd like to see some testing done to provide quantitative results.

Thoughts?

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post #12 of 22 (permalink) Old 05-02-2008, 11:10 AM
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deppends what your talking about as in if you put the duals on a 96 4.6 bone stock npi the duals may flow better than the 3.5". on a 200hp npi stock motor the 3.5 may result in poorer scavenging than the duals as in =less flow???? idk??/

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post #13 of 22 (permalink) Old 05-02-2008, 12:34 PM
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deppends what your talking about as in if you put the duals on a 96 4.6 bone stock npi the duals may flow better than the 3.5". on a 200hp npi stock motor the 3.5 may result in poorer scavenging than the duals as in =less flow???? idk??/
Nowhere in my post did I say which will make more power. That is ENTIRELY application dependant. All I said was that a single 3.5 has more flow capacity than dual 2.5's.

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post #14 of 22 (permalink) Old 05-02-2008, 01:07 PM
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my bad and i totally agree on that! A 3.5 single should have more flow capacity

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post #15 of 22 (permalink) Old 05-02-2008, 05:13 PM
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...I'd say the 3.5 single will outflow two 2.5, in equal setups (same length, same bends). My reasoning is that line loss in fluid flows result from the fluid shear present where the fluid is moving against the pipe....

Thoughts?
Correct.

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post #16 of 22 (permalink) Old 05-02-2008, 10:44 PM
 
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Mike is running 3.5" single on his blown mark viii . Is there any other MN12 or FN10 car running single 3.5" out there?
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post #17 of 22 (permalink) Old 05-03-2008, 03:42 AM
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Mike is running 3.5" single on his blown mark viii . Is there any other MN12 or FN10 car running single 3.5" out there?
David Neibert is running a mandrel bent 3.5" mid-section on his 10 second SC.

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post #18 of 22 (permalink) Old 05-03-2008, 10:08 AM
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We are running Smokymance's old set up on the SVO car.

Catless down pipes with a magnaflow midmount and a 3inch mandrel after the midmount.

The car pulls alittle harder in the upper RPM's.

Torque lost is not noticable.Hell it has an SVO M112 on it.

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post #19 of 22 (permalink) Old 05-09-2008, 08:46 PM
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100% guessing. I vote 3.5" for HP and 2x2.5" for torque.

But in all actuality, I say to be able to come to any sort of conclusion.. DYNO TIME! It's just so dynamic. If the sources were equal for both setups, I'd say 3.5" too, just my thinking. But, the sources wouldn't be the same. One 2.5" would be fed by 4 cylinders... the 3.5" would be fed by eight... and even then, both setups would typically be post catalytic-converter. In any cause, unless something is horribly wrong, I'd say the differences would be almost neglible.. and would place different events at different RPMs.

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post #20 of 22 (permalink) Old 05-30-2008, 01:55 PM
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The 3.5" pipe would literally flow more than two 2.5", even if the area were exactly the same, it has less wall surface to add friction to the flow. Exhaust gas or water or marbles or BBs.

Dual 2.5" would have a more pleasant note. Likely mufflers added to the systems would shift the advantage to the dual 2.5" set up as most of the available mufflers that would fit under these cars and fit a 3.5" pipe are going to be more restrictive than two simular sized mufflers with 2.5" inlets.

My old 454 Chevelle had only 2.5" pipes yup front and 1.875" tail pipes after the mufflers (which cooled the gases and thus allowed same flow of now smaller volume). It ran OK, sounded OK. The old Chrysler performance cars of the '60s which had the best sound of any car IMHO, like the 383s and 440s (and my 340 Swinger) had 2.25 head pipes (Hemi had 2.5"head pipes) and 1.875" tail pipes after the mufflers, they did OK too.

These bigger pipes many use now on street cars have a "fluffy" sound in comparison to the "sharp crackle" heard back then due to slower velocity of the gasses.

Just not a fan of oversized pipes and wheels I guess.

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post #21 of 22 (permalink) Old 05-30-2008, 08:58 PM
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less pipe = cheaper too ahaha sorry had to...

but honestly on a stock 4.6 in a bird, i would think that the differences would be minimal and like 94DD4.6 said, each 2.5" is only flowing 4 cylinders worth of exhaust, where the 3" or 3.5" is flowing all 8....so i dont think it can be compared as easily. but if it were me, id maybe find a happy medium and go a 3" NOT 3.5" single, and going on what some others have said, less pipe becasue of the less bends (again minimal anyways) but also would be cheaper as well.

another reason id go 3" and not 3.5" is yes 3.5" will flow same as dual 2.5" but like others have said low end TQ may suffer so id cut it down to 3" to maybe recover some of that lost low end.

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post #22 of 22 (permalink) Old 05-31-2008, 11:31 PM
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Quote:
Originally Posted by 94 Daily Driven 4.6L View Post
But not the normal one.

If the area measurement between a dual exhaust and a single exhaust is the same, will one make more power and/or torque than the other?

For example:
Dual 2.5" = 9.82 sq in total area
Single 3.5" = 9.89 sq in total area

Which one will provide the best horsepower and which will provide the best low end torque?

And why!!
if exhaust is all you are planning to do (or minimal modifications to the motor as well), pick whichever is cheaper because the difference in power is going to be so small there wont be a noticible difference.

the usual chatter about loss of low end and stuff is somewhat bs. its not that you're losing low end per-se. it has more to do with the complete system as a whole, all mods included i mean. you open up the exhaust so you can flow more air into the motor. basically you're moving the powerband UP. essentially you are gaining power just in at different rpms from stock.

its a domino effect, change the exhaust leads to changing the air intake side which leads to changing when the valves open/close, which changes how much fuel is used, which changes where you need to spool up the gears in order to reach optimum powerband which leads to needed to stall at a different rpm...so on and so on. its a misconception that you "lose low end" power, its not that its lost, its just that you're changing where your power happens. once thats understood then one can start planning out what set up they'll go with in its entirety.
if your just looking for a little boost in power and some sound, id go with 2.5 inch true duals because they sound alot better than a y pipe (y - intermediate pipe, exits) set up imho. 3.5 inch true duals would be absolutely overkill unless ur planning to dig into that motor and im not taking the standard PI swap which 2.5 duals are a perfect match up for that swap.

sorry for the novel lol

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