Engine Masters - Dual vs Single Exhaust

[Cooter_76]

I swear I'm not a shill for MotorTrend on Demand, but there's a new episode of Engine Masters that would help settle a lot of exhaust discussions on this forum.
They dyno test a 420HP 351 with 2.5" dual exhaust vs 3" single exhaust. Both combos are also tested with turbo mufflers vs flow-through (Magnaflow style) mufflers.
Spoiler alert: The 3" single won, but ONLY with a flow-through muffler. The single exhaust with the turbo muffler was the worst of the bunch.

 

[phred]

So how bad was the turbo style single. I really like a super single set up as it leave room under the truck and is easier to clear the transfer case. BC Broncos did some dyno work on their super single set up and if memory serves it worth about 10 hp over a standard dual set up.


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[Broncobowsher]

They flawed it. They used a single small oval case turbo muffler. The results would have been different if they used a large case turbo muffler. If they band sawed that 3" turbo in half they would have found why it is so restrictive. The way the exhaust is pinched crossing from side to side by the shell walls as it passes over the inlet tube that runs full length.

And the final conclusion is the 3" head pipe was a bigger difference. The 3" single was 100% 3" pipe all the way to the collector. So dual 3" merged into a single 3" compared to dual 2½". They were commenting on how mixed there results are and it left more questions than answers.

 

[Cooter_76]

They flawed it. They used a single small oval case turbo muffler. The results would have been different if they used a large case turbo muffler. If they band sawed that 3" turbo in half they would have found why it is so restrictive. The way the exhaust is pinched crossing from side to side by the shell walls as it passes over the inlet tube that runs full length.

I'm no turbo muffler expert, but which version is most commonly found in a dual exhaust kit sold for a Bronco?

And the final conclusion is the 3" head pipe was a bigger difference. The 3" single was 100% 3" pipe all the way to the collector. So dual 3" merged into a single 3" compared to dual 2½". They were commenting on how mixed there results are and it left more questions than answers.

Fair enough, but I still thought it was pretty interesting.

 

[Cooter_76]

So how bad was the turbo style single. I really like a super single set up as it leave room under the truck and is easier to clear the transfer case. BC Broncos did some dyno work on their super single set up and if memory serves it worth about 10 hp over a standard dual set up.

Here are some screen shots:

Max numbers for dual turbo vs dual straight-through:

Chart for comparison:

Max numbers for dual vs single turbo:

Chart comparing best dual run vs single turbo:

Max numbers for all four versions:

Chart comparing dual straight-through vs single straight-through:

 

[blubuckaroo]

And I'll be that 3" flow through was really loud too.
What's the reason for a muffler?

 

[Spaggyroe]

I would've liked to have seen them test dual 2.5" head pipes, into a Y collector, with 3" flow through muffler.

Interesting episode though.

 

[Broncobowsher]

Yes, 2 2-1/2 into a single 3". I think they realize that but didn't have the parts to do it on film day.

I want to see what a proper big bore turbo style muffler would do https://classicbroncos.com/forums/showpost.php?p=3272848&postcount=25

 

[DirtDonk]

And I'll bet that 3" flow through was really loud too.
What's the reason for a muffler?

"Again with the negative waves Moriarty!"
Lots of us run straight-through mufflers on the street (including me, who hates loud anymore). Most of which are quite subdued in their sound.
How many hundreds of thousands of Magnaflows, Gibsons, Dynomax Ultra-Flows, and even new glass-pack types do you think there are out there? Many...
And all are straight through.

When done right, they can be quieter than some turbos. If sized or designed wrong, sure they can be loud. But probably no louder than a 30-series Flowmaster that is not straight through.

Basically, straight through or not, it's still called a muffler for a good reason. And it's why there's a full chamber around the straight through section on some, and whatever perforation magic the new Cherry Bomb and other brands of modern "glass-packs" use to quiet things down.

Paul

 

[brewchief]

What I took away from it was if your going to run a single exhaust on a performance motor you need to use a muffler that can handle the flow needed.

Both straight through and baffled mufflers are available that will work. The turbo muffler they used simply didn't flow well enough.

I would have liked to see that test run with the T connection and the straight through muffler, it would have shown how bad the T vs Y connection really is or isn't.

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[68ford]

It would be nice to know the header primary diameter and type of collector. If a barely good enough header was being used it makes what you do down stream not as important. If it had a nice seat of tuned stepped headers with merge collectors, it would be nice to see the results.
My 438 Windsor makes 565 HP at 5600 and 570 TQ at 4400 through about 3 foot of 3.5 single pipe that splits into dual 3in with MagnaFlow race mufflers. Headers step twice. 1 3/4 up to 1 7/8 up to 2in. And has merge collectors not normal formed collectors

 

[spap]

It would be cool if they showed the HP and TQ below 3000 rpm,

 

[rmk57]

It would be cool if they showed the HP and TQ below 3000 rpm,

Exactly, unless you drive around at 6200 rpm the numbers are mostly pointless.

 

[brewchief]

Dyno numbers are at wide open throttle so they wouldn't apply unless you're driving around at 2500 rpm and wide open throttle.

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[chuck1022]

I love Engine Masters. I have watched every single one....some multiple times. I take all this with a grain of salt as they are mostly wide open throttle drag racer types.

I want an engine that runs great from 900rpm to 4000rpm.

Watching that show really illustrated to me that headers are not worth it (to me).

 

[Broncobowsher]

It would be cool if they showed the HP and TQ below 3000 rpm,

The issue is the dyno. It only has so much of an RPM window. Since they typically deal with 7000+RPM race engines it has to handle the high RPM. The absorber just can't run that low.

Hotrod Garage did a 3 engine build out. LS, 6BT, Toyota 6-cylinder. The Cummins doesn't build the RPM of the other engines. They had to shop around to find a dyno that could get any numbers on the 6BT as it tops out about where most dynos start loading an engine at.

I am sure if all you did was diesel engines you can buy a dyno that will pull those low RPM numbers. Years ago we played on a chassis dyno and I set the transmission to hold 3rd gear no matter what and manually locked the convertor. I would get a rolling start, hit 3rd and lock the convertor. I could pull numbers down at 1000 RPM. But that is an inertia dyno, knowing the inertia of the roller and how fast you spin it up it know how much HP it takes to accelerate it. It actually measures HP and back calculates torque. Where the engine dynos are absorber dynos. There is a water brake, very much like a torque convertor, that varies the load based on waterflow through the water brake. It is on a scale, basicly a giant torque wrench. That does record torque and calculates HP.

The neatest dyno I remember was a Caterpillar. The new engines were hooked to an electric motor and spun up without any fuel put into them. By recording the torque profile they could check nearly everything with the engine. Internal drag, cam timing, compression, etc. After the engine proved it was built right then fuel was put to it for the factory break in.

Manufacturing and R&D dynos are almost always electric. The big aircraft engines factories of WWII used the engine break in to partially power the manufacturing plants. That would have been an impressive room to be in. Rows of V12 aircraft engines running full power. OK, I degressed. the dyno they have simply can't make data down that low.

 

[ZOSO]

"Again with the negative waves Moriarty!"
Lots of us run straight-through mufflers on the street (including me, who hates loud anymore). Most of which are quite subdued in their sound.
How many hundreds of thousands of Magnaflows, Gibsons, Dynomax Ultra-Flows, and even new glass-pack types do you think there are out there? Many...
And all are straight through.

When done right, they can be quieter than some turbos. If sized or designed wrong, sure they can be loud. But probably no louder than a 30-series Flowmaster that is not straight through.

Basically, straight through or not, it's still called a muffler for a good reason. And it's why there's a full chamber around the straight through section on some, and whatever perforation magic the new Cherry Bomb and other brands of modern "glass-packs" use to quiet things down.

Paul

When I built my exhaust I ran 2-2.5" into a single 3in with an 18in magnaflow. I started the bronco with the muffler and about 10" of pipe after. It had a great sound and was relatively quiet. I finished out building the tailpipe and the longer the pipe after the muffler the louder the exhaust note became.

 

[rguest3]

I prefer the 2-into-1 exhaust.

Headers and 2 1/2" Pipe into Dual Inlet Gibson Superflow Muffler with 3" Outlet to Stock Tail Pipe location.

 

[ZOSO]

It would be nice to know the header primary diameter and type of collector. If a barely good enough header was being used it makes what you do down stream not as important. If it had a nice seat of tuned stepped headers with merge collectors, it would be nice to see the results.
My 438 Windsor makes 565 HP at 5600 and 570 TQ at 4400 through about 3 foot of 3.5 single pipe that splits into dual 3in with MagnaFlow race mufflers. Headers step twice. 1 3/4 up to 1 7/8 up to 2in. And has merge collectors not normal formed collectors

I think one of the early episodes they did a comparison with a 1.5" or 1 5/8ths headers to a 1 3/4" or 1 7/8" header and the results were pretty good. But in reality many of us are 300hp at best and don't search for every last hp available.

 

[nvrstuk]

I think one of the early episodes they did a comparison with a 1.5" or 1 5/8ths headers to a 1 3/4" or 1 7/8" header and the results were pretty good. But in reality many of us are 300hp at best and don't search for every last hp available.

Yeah... I'm not one of those "many" you refer to... I go to no end (almost) to get all I can out of anything and everything on my rig. Just what I like to do.

I am currently still looking for larger primary tube headers for my engine. Dual 3" mandrel to 21" bodied UltraFlows to help quiet it down... some. I had 14" bodied mufflers but it was so loud and obnoxious... so I lowered the floors and moved body mounts, floor stiffners, you name it for the larger mufflers. Helped a lot. I am pushing 600 HP/710ft lbs of torque thru those mufflers so breathing is important.