Which has better exhaust flow?

13244 Views 21 Replies 15 Participants Last post by turbo2256b, Jul 2, 2010

Rlzegers

Discussion Starter · Jun 28, 2010

Really basic question here. All other things being equal, which has better flow, 2-1/4" duals or 3" single exhaust? I have a 460 I tow with that has 2-1/4" dual exhaust and a friend insists that 3" single exhaust would provide better overall flow. I'm using truck exhaust manifolds and Flowmaster 40 series mufflers, Holley 670 cfm carb, recurved Duraspark, Lunati Bracketmaster II cam and Weiand 8012 intake.

Thanks,

Ron

1 - 20 of 22 Posts

obxboarder

· #2 · Jun 28, 2010

flow

i think the dual would flow better as long as it is true dual exaust but those flowmasters are the downfall get some magnaflows they work much better

Cambi

· #3 · Jun 28, 2010

2 and 1/4 is 1.6L Honda sized exhaust. Why even bother? My 3" true duals were about $400 to fab up, sounds amazing, and makes just as much if not more power than open headers.

CarsByCarl

· #4 · Jun 28, 2010

Single 3" has a slight edge.

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Rlzegers

Discussion Starter · #5 · Jun 28, 2010

Thanks Carl. That's the information I was looking for.

Ron

rmcomprandy

· #6 · Jun 29, 2010 (Edited)

CarsByCarl said:
Single 3" has a slight edge.

I don't really know one way or the other but, on the chart you show here, a single 3" will max at 300 HP and a dual 2 1/2" will max at 400 HP.
Just reading your chart as it is presented ...

EDIT: I see now that I read the original post wrong ... 2 1/4" tubing certainly is not the same as 2 1/2" tubing .

bigblok86ranger

· #7 · Jun 29, 2010

Cambi said:
2 and 1/4 is 1.6L Honda sized exhaust. Why even bother? My 3" true duals were about $400 to fab up, sounds amazing, and makes just as much if not more power than open headers.

I ran over 450hp through 2 1/4" exhaust and also through 3 inch and made no difference in ET at all not even .001 of a second so I would say his exhaust is sufficient.

I talked to Flowmaster about exhaust pipe sizing and I was told that in their testing that they noticed no hp difference between 2 1/4 and 2 1/2" exhaust systems only measureable difference was about 50 decibals.

nickbay

· #8 · Jun 29, 2010

Rlzegers said:
Really basic question here. All other things being equal, which has better flow, 2-1/4" duals or 3" single exhaust? I have a 460 I tow with that has 2-1/4" dual exhaust and a friend insists that 3" single exhaust would provide better overall flow. I'm using truck exhaust manifolds and Flowmaster 40 series mufflers, Holley 670 cfm carb, recurved Duraspark, Lunati Bracketmaster II cam and Weiand 8012 intake.

Thanks,

Ron

Using the formula area = diameter/2 squared X pi we get:

dual 2.25" = 7.95
single 3" = 7.06

So dual 2.25" pipe has more area for what it's worth

CarsByCarl

· #9 · Jun 29, 2010 (Edited)

rmcomprandy said:
I don't really know one way or the other but, on the chart you show here, a single 3" will max at 300 HP and a dual 2 1/2" will max at 400 HP.
Just reading your chart as it is presented ...

I think he asked 2.25 dual vs. 3.00 single. The chart is from Flowmaster. Don't know how they're figuring HP, but I do think it's a fair representation of restriction.

CarsByCarl

· #10 · Jun 29, 2010

nickbay said:
Using the formula area = diameter/2 squared X pi we get:

dual 2.25" = 7.95
single 3" = 7.06

So dual 2.25" pipe has more area for what it's worth

Yes, but the duals have more surface friction.

Filucky

· #11 · Jun 29, 2010

I read a story on a 460 tow rig build up, they had a little better flow from a single 3" but the dual 2 1/4 or 2 1/2 (cant remember) had better heat transfer and they liked that better for a dedicated tow rig.

Rlzegers

Discussion Starter · #12 · Jun 29, 2010

Filucky said:
I read a story on a 460 tow rig build up, they had a little better flow from a single 3" but the dual 2 1/4 or 2 1/2 (cant remember) had better heat transfer and they liked that better for a dedicated tow rig.

Truth is the muffler shop wanted to install a 3" single but I opted to go dual because I like the look and sound better. They suggested 2 1/4 over 2 1/2" diameter to help out lower end torque. That's what I went with. I haven't been sorry. Besides, doesn't dual exhaust look cool on a 1978 Ford truck?

Ron

DaveMcLain

· #13 · Jun 30, 2010

A larger amount of area is probably better as in a larger pipe but the question is one of fitting it onto the truck. A larger pipe might flow more but it also might lose more flow because the bend radius in the corners are closer to the diameter of the pipe and therefore tighter/closer to a kink than they would be on a smaller pipe....

In a system that's completely un tuned I doubt there is any advantage to running a 2 1/4 diameter pipe vs a 2.5 or 3 inch.

Filucky

· #14 · Jun 30, 2010

Rlzegers said:
Truth is the muffler shop wanted to install a 3" single but I opted to go dual because I like the look and sound better. They suggested 2 1/4 over 2 1/2" diameter to help out lower end torque. That's what I went with. I haven't been sorry. Besides, doesn't dual exhaust look cool on a 1978 Ford truck?

Ron

I ran dual's on all three of my '79 Fords. One F250 and two Bronco's, all had 460's.

2slow

· #15 · Jun 30, 2010

CarsByCarl said:
Yes, but the duals have more surface friction.

that thinking would have stock 302 ports on a 600 cube engine for the less surface area = less friction = more flow . I don't think so

crittersf1

· #16 · Jun 30, 2010

The only way to know is to put it on a DYNO with both systems.

DaveMcLain

· #17 · Jun 30, 2010

A year or two ago we did some testing on a customer's 505 inch big Chevy where we used the whole exhaust system from his truck. We had been testing the engine with a set of headers, a 12 inch collector extension and a set of Magnaflow mufflers(3 inch collector and muffler).

The customer was convinced that we'd see some serious losses in the exhaust system that he had to run in his mud racing class so we put it to the test. It looked funny having all that twisted up pipe sticking out there and supported by a couple of jack stands but it was worth the effort. The exhaust was a 3 inch pipe with some very tight bends near the header to make it get around the transmission and transfer case. By FAR the biggest loss in the system was in the mufflers(Flow masters). Removing those mufflers and substituting the Magnaflows or some $10 glasspacks made the system work as well as the baseline.

This engine was a low 8.4:1 compression hydraulic cammed dual plane intake setup that was making 430 horsepower at 5000rpm and about 530lbs/ft torque at 2800rpm so it was extremely mild. With that said I was wondering if being low compression would make it more sensitive to an inadequate exhaust system.

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johnnywalker

· #18 · Jul 1, 2010

what was the power loss with the flowmaster vs the 10.00 dollar muffler ?

MauriSSSio

· #19 · Jul 1, 2010

do 3" duals really start becoming a restriction at only 500hp?

Mark Miller

· #20 · Jul 2, 2010

Was wandering the same thing i have 2" Headers with 3 1/2" collectors with 3" exhaust with Magnaflow mufflers.466 Flat top piston,A-429 Cj heads very little port work,Victor Intake,Holley 1,000 cfm HP carb,.670-.690 Solid Roller cam 256-266 duration at .050.

Thanks Mark.

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