3" single exhaust instead of duals
- Thread starter mattri
- Start date
There's no imbalance in any I6 exhaust system, so that's not an issue.
In general, the fewer bends and transitions, the better. The y-pipe creates backpressure unnecessarily. If you want a single, you're better off going into a 2 into 1 muffler.
In general, the fewer bends and transitions, the better. The y-pipe creates backpressure unnecessarily. If you want a single, you're better off going into a 2 into 1 muffler.
Howdy Matt:
One advantage to a single exhaust pipe and muffler is less weight.
For balance and scavanging to have an effect you would have to tune for a specific rpm, and probably have to design a 180 degree system. After all that the gain on our engines would likely be very small and very specific. I do love the sound of 180 degree exhaust headers though.
A 3" pipe is over kill. A 2.5" system is more than adequate. This kind of single outlet exhaust system may improve low end torque, over a comparable dual system. This advantage would likely reverse itself at high rpms.
Adios, David
One advantage to a single exhaust pipe and muffler is less weight.
For balance and scavanging to have an effect you would have to tune for a specific rpm, and probably have to design a 180 degree system. After all that the gain on our engines would likely be very small and very specific. I do love the sound of 180 degree exhaust headers though.
A 3" pipe is over kill. A 2.5" system is more than adequate. This kind of single outlet exhaust system may improve low end torque, over a comparable dual system. This advantage would likely reverse itself at high rpms.
Adios, David
A
Anonymous
Guest
Aha! Matt, there's more to this than you think, and I've got questions for the gurus here.
Why are dual exhaust pipes considered better than one? One pipe, given the same cross-sectional area as the total of your two-pipe system, will have much less total circumference, thus less skin-friction, less resistance to flow. Gas-flow through a tube, like waterflow in a river, is fastest in the middle, slowest at the draggy edges. Furthermore, since dual pipes have more surface area than our larger-diameter single pipe, they will disipate heat to the outside air more easily. As the temperature of the exhaust gases drops, their energy decreases, and wavespeed slows. This is one of the reasons people are wrapping exhaust systems with thermal barriers.
Clue us in, StrangeRanger! Why isn't a single exhaust (after the muffler) better than two?
Why are dual exhaust pipes considered better than one? One pipe, given the same cross-sectional area as the total of your two-pipe system, will have much less total circumference, thus less skin-friction, less resistance to flow. Gas-flow through a tube, like waterflow in a river, is fastest in the middle, slowest at the draggy edges. Furthermore, since dual pipes have more surface area than our larger-diameter single pipe, they will disipate heat to the outside air more easily. As the temperature of the exhaust gases drops, their energy decreases, and wavespeed slows. This is one of the reasons people are wrapping exhaust systems with thermal barriers.
Clue us in, StrangeRanger! Why isn't a single exhaust (after the muffler) better than two?
A
Anonymous
Guest
Matt, David & Smitty are on to something.
My research shows that a 2" exhaust pipe will be fine at engine speeds below about 4,000 rpm. Above that backpressure will start to hurt performance, I would recommend a 2 ¼†exhaust pipe to 150 bhp or 5,000 rpm and 2 ½†exhaust pipe from 150 bhp to 200 bhp or 5,500 rpm and above all the way back to a single turbo muffler of the same diameter inlet and outlet designed for the displacement of the engine. Dual exhausts are for bent eights! IMHO
My research shows that a 2" exhaust pipe will be fine at engine speeds below about 4,000 rpm. Above that backpressure will start to hurt performance, I would recommend a 2 ¼†exhaust pipe to 150 bhp or 5,000 rpm and 2 ½†exhaust pipe from 150 bhp to 200 bhp or 5,500 rpm and above all the way back to a single turbo muffler of the same diameter inlet and outlet designed for the displacement of the engine. Dual exhausts are for bent eights! IMHO
A
Anonymous
Guest
But why are dual exhausts better for anything?
Howdy SS and All:
There are several ongoing factors in this answer.
1. On a big inch, big buck V8 a dual system is an efficient way to gain performance. In the days of the factory muscle cars these dual systems used a heat riser to block off one sides exhaust with a bi-pass valve to increase and hurry heat to the intake manifold and carb. If the big block factory hot rods do duals then it must be good for all.
2. The coolness factor. Just like some folks have to have multi carbs when one will do the job better. A tri-power is the ultimate cruise night coolness factor. Dual exhaust is a necessity. It can't be hot with a lowly single exhaust, even if it is lighter, more efficient and cheaper.
3. Finally tradition and sound. A split manifold on a chevy six with Smitty's was heavenly. I was younger then. It's tough to get past those good memories and tradition.
There are probably other factors too, but that's all I could think off at the moment.
Adios, David
There are several ongoing factors in this answer.
1. On a big inch, big buck V8 a dual system is an efficient way to gain performance. In the days of the factory muscle cars these dual systems used a heat riser to block off one sides exhaust with a bi-pass valve to increase and hurry heat to the intake manifold and carb. If the big block factory hot rods do duals then it must be good for all.
2. The coolness factor. Just like some folks have to have multi carbs when one will do the job better. A tri-power is the ultimate cruise night coolness factor. Dual exhaust is a necessity. It can't be hot with a lowly single exhaust, even if it is lighter, more efficient and cheaper.
3. Finally tradition and sound. A split manifold on a chevy six with Smitty's was heavenly. I was younger then. It's tough to get past those good memories and tradition.
There are probably other factors too, but that's all I could think off at the moment.
Adios, David
A
Anonymous
Guest
Maybe the factories did it for coolness, tradition, and sound. I'm not saying those factors have no value (smiley face here), but I still have my doubts. It might be that a big V-8 has to have two mufflers to avoid running out of breath. But if a big block had a single 2-into-1 muffler as big as a bus or truck muffler, I'm suggesting that one outlet pipe is more efficient than one. Well??
one three inch mandrel bent pipe will flow almost twice as much as two 2.5" pipes (has to do with velocity gradients and such) imho 2" dual are as big as are needed on a NA six with 2.5" single being the single pipe option (prob too big even anyway) for a turbo car go as big as you can fit. on a turbo 200 I would think a set of 2.5" duals or a 3" single would be where you want to be. 3" would be best but if you have some space restraints go with the 2.5"
In the grand scheme of things, they aren't...Seattle Smitty":r5dfzkpo said:
Back in the day, Smokey Yunick experimented with fabricating equal tube length 8-into-one headers (on a V-8, obviously). In the effort to get the header into engine bay, the damned thing ended up looking like an octopuss trying to swallow the engine. But it worked... IIRC he netted something like an additional 4-5 HP over the dual out setups. :roll: He never did it again...
But the I6 would definitely be easier to accomplish of course. But as SR alludes to, you'd have to design a Y-pipe/collector that didn't create any backpressure for the effort to be worthwhile.
I never said duals were better. He already has 2 downpipes coming off his headers. The question is what to do with them. Merging them together into a y-pipe simply may not be as efficient economically or technically as running them into a dual inlet muffler (or a dual inlet cat if applicable.) What to do with the output then becomes the question. I would favor the 3" single over the 2" or 2.25" duals for all the reasons stated above.
A
Anonymous
Guest
is there such thing as a dual inlet cat? i'm going to be dealing with the same thing with my dual outlet headers. i'm just wondering if i'm going to be forced to use a y-pipe.
Catco 9513
A
Anonymous
Guest
Man, you are really on top of this stuff!!!!!
Literally true. There's one just under the cab of my F150.Seattle Smitty":2jwgg714 said:
Why do people have to lungs? Because its impossible to have the area of a basketball court in your chest unless you have two bags. This creates more surface area, more flow loss, but better oxygenation
Skin friction decreases with size.
In the case of lungs, two bags beat one. In the street six or tow car truck, it is also the case, but for another reason; gas speed.
Despite two small pipes have more wetted perimeter than one large pipe, and are more restrictive, they promote signifcant low end torque and a sweeter sound.
The old Mannings channel flow has wetted perimeter of wetted area as a method of determining headloss, and let me tell ya, its conclusive. Dual pipes are no match for a bigger single pipe for peak flow.
Example:
On a little 200 cube six, two 2" ID pipes 12 feet long have a internal surface area of 6.283 square feet each, or 12.57 sq feet for both. It's cross sectional area is 0.0218 square inches each, or 0.044 square inches total.
The equivalent single pipe has to be a huge 2.83" diameter, and has an internal area of 8.89".
The peak gas speed on the smaller, larger internal surface dual exhast system is heaps higher than on the single pipe, which is where the extra torque comes in. A big single should not be the first option.
The reason for favouring the option of using a dual system is cost and the fact that an exhast system has to meet a a crtical flow speed. Going to a big pipe drops the flow speed and maximum torque, even though peak power increases. This is why engine programs development programs focus on dyno tuning dual pipes giving better torque. On cars with Watts links or fuel tanks in the way, a big single is often the only option. This is the case of Aussie Holdens with2.25" singles and 3.8 liter Buick engines, and also the XR6 Falcons, which have severe space limits becasue of the under trunk and seat restrictions.
Race exhasts don't suit road cars. If everywhere was Laguna Seca, we'd all have 3" single pipes.
V8 dual pipes are cheap, simple, and give lower restriction per dollar spent. Big pipes don't isloate noise well, fail to build up low end torque, and need more expensive mufflers.
The tip on Y-pipes is that any thing that is like a valve is an unaerodynamic restriction. The ones which don't allow a standing wave to travel back up the pipe work; the dual out headers to a H-pipe then to a dual have no restriction. Similarly, onn a V8, X and H pipes are fine. Y-pipes are a potential proplem that require specific design to eliminate a wave backing up to the exhast header at the engine. Angles which make it y and not Y shape work best. Ford Australia used tri-y headers on the 1971 Falcon GTHO to improve high end power with no loss in low speed torque.Despite a milder cam, it gaveimproved performance.I'm not sure about NASCARS but the AVESCO racers in Aussie X pips and dual pipes with huge success. No big phat singles anymore. You don't have to use them.
On the street, the back pressure must be reduced without a major drop in gas speed. Using two pipes halfs the back pressure. Using two big v8 pipes is the optimum. Any bigger, and you loose torque and gain noise. Why do 20 valve Toytota Celicas and Corolla's use dual pipes on 121 cube engines? To reduce the back pressure and make it sound nice.
We've all got a lot to re-learn about the good old six cylinder exhast. Chrysler Australia taught it all with the 14.4 second 1/4 mile 4.3 liter Valiant Charger E49.
Base six, 185 hp. Stock exhast, single branch. Optional 205 hp Pacer, dual out header.
Triple carb E38, single tuned length header with dual exhast. No change in exhast from the 248 hp six pack to the final 302 hp E49 six pack.
Same exhast on the 340 E55 Charger with the US 275 engine was very restrictive. The Aussies learned in 1972 that the right size exhast gives the right kind of power and torque.
On the race track, the little dual piped triple carb 302 hp 265 cube six out torqued and out accelerated the big 350 plus hp Cleveland 351 4V Falcon GT's. At the drags, the six did 14.4 second qaurters, the 351 a 14.7 second quarter.
Your sixes, with the right dual exhast system, should do the same thing. Performance single and twin cam Six inliner BMW's, Mercedes, Lexus, they all run dual out exhasts, not singles. Always have done.
Skin friction decreases with size.
In the case of lungs, two bags beat one. In the street six or tow car truck, it is also the case, but for another reason; gas speed.
Despite two small pipes have more wetted perimeter than one large pipe, and are more restrictive, they promote signifcant low end torque and a sweeter sound.
The old Mannings channel flow has wetted perimeter of wetted area as a method of determining headloss, and let me tell ya, its conclusive. Dual pipes are no match for a bigger single pipe for peak flow.
Example:
On a little 200 cube six, two 2" ID pipes 12 feet long have a internal surface area of 6.283 square feet each, or 12.57 sq feet for both. It's cross sectional area is 0.0218 square inches each, or 0.044 square inches total.
The equivalent single pipe has to be a huge 2.83" diameter, and has an internal area of 8.89".
The peak gas speed on the smaller, larger internal surface dual exhast system is heaps higher than on the single pipe, which is where the extra torque comes in. A big single should not be the first option.
The reason for favouring the option of using a dual system is cost and the fact that an exhast system has to meet a a crtical flow speed. Going to a big pipe drops the flow speed and maximum torque, even though peak power increases. This is why engine programs development programs focus on dyno tuning dual pipes giving better torque. On cars with Watts links or fuel tanks in the way, a big single is often the only option. This is the case of Aussie Holdens with2.25" singles and 3.8 liter Buick engines, and also the XR6 Falcons, which have severe space limits becasue of the under trunk and seat restrictions.
Race exhasts don't suit road cars. If everywhere was Laguna Seca, we'd all have 3" single pipes.
V8 dual pipes are cheap, simple, and give lower restriction per dollar spent. Big pipes don't isloate noise well, fail to build up low end torque, and need more expensive mufflers.
The tip on Y-pipes is that any thing that is like a valve is an unaerodynamic restriction. The ones which don't allow a standing wave to travel back up the pipe work; the dual out headers to a H-pipe then to a dual have no restriction. Similarly, onn a V8, X and H pipes are fine. Y-pipes are a potential proplem that require specific design to eliminate a wave backing up to the exhast header at the engine. Angles which make it y and not Y shape work best. Ford Australia used tri-y headers on the 1971 Falcon GTHO to improve high end power with no loss in low speed torque.Despite a milder cam, it gaveimproved performance.I'm not sure about NASCARS but the AVESCO racers in Aussie X pips and dual pipes with huge success. No big phat singles anymore. You don't have to use them.
On the street, the back pressure must be reduced without a major drop in gas speed. Using two pipes halfs the back pressure. Using two big v8 pipes is the optimum. Any bigger, and you loose torque and gain noise. Why do 20 valve Toytota Celicas and Corolla's use dual pipes on 121 cube engines? To reduce the back pressure and make it sound nice.
We've all got a lot to re-learn about the good old six cylinder exhast. Chrysler Australia taught it all with the 14.4 second 1/4 mile 4.3 liter Valiant Charger E49.
Base six, 185 hp. Stock exhast, single branch. Optional 205 hp Pacer, dual out header.
Triple carb E38, single tuned length header with dual exhast. No change in exhast from the 248 hp six pack to the final 302 hp E49 six pack.
Same exhast on the 340 E55 Charger with the US 275 engine was very restrictive. The Aussies learned in 1972 that the right size exhast gives the right kind of power and torque.
On the race track, the little dual piped triple carb 302 hp 265 cube six out torqued and out accelerated the big 350 plus hp Cleveland 351 4V Falcon GT's. At the drags, the six did 14.4 second qaurters, the 351 a 14.7 second quarter.
Your sixes, with the right dual exhast system, should do the same thing. Performance single and twin cam Six inliner BMW's, Mercedes, Lexus, they all run dual out exhasts, not singles. Always have done.
A
Anonymous
Guest
Hmmm. Can you isolate the effect of pipe diameter on exhaust flow so neatly? You mention two 12' pipes on a street car, but if you raced the car the pipes might want to be 3-4' or whatever. What about the effect of diameter (and surface area) on heat dissipation; does a single pipe with the same cross-sectional area (but less surface) as your duals retain heat (and energy) in the exhaust charge enough better to measure, or is that a negligible effect? Suppose you wrapped the whole system with thermo-tape from front to back (esp. the muffler, which surely loses the most heat); could you then employ the single large low-drag pipe on a street car? Or, to state it from the other direction, my '71 MerBenz 2.8 six has small dual pipes, a muffler, and a resonator, all radiating heat. If I wrapped the whole system in thero-tape, would the small pipes be more "draggy" at high outputs?
Don't read this unless you have a desire to befriend the village idiot. It was a late night ramble.
The critical inputs of just the pipes are
Q, the flow in CFM, (You must have good CFM flow at 25"Hg for the mufflers, its is critical).
v, the peak velocity, and
a, the area.
The total volume,
surface area and
cross sectional area to each cube of engine is very important too, but the engine programs give guidlines for race engines, not streeters.
These all govern back pressure
A big single will always do better for maximum power than a smaller set of duals. But low and mid range torque can die if the gases are not extracted quickly, and the tone of the engine suffers in day to day use, becoming trumbone like and tending to reverberate. Check out a ricer with a big gun exhasts on a four cylinder engine. Deeper and more like a Model A. At the dizy heights of the power curve, a reduction of backpressure with the right fuel mixtures always raises power. Always.
As said, Ford and Holden in Aussie always use singles now on the sixes, but the V-8's run dual set-ups. The reason is the sixes are cheaper, and the eights are the image makers for each company. The thermal loss due to having dual exhasts will be greater, but the sound energy is more restrained, and at a higher pitch with twin pipes. Thermal wrap will upset the designers cooling of the exhast valves, as 25% of energy is going out via the pipes. Valve seat resession, cooling due to guide area is now upset.
David Vizard has some most awesome flow figures in his Mini and Ford SOHC books. He nails back pressure as the be all an end all the performance. Then he goes head hunting reverse waves like some kinda dragon slayer brandishing a flow bench. He specifies ideal types of silencer, and rates them in terms of standing waves very comprehensively. Then he just says to heck with megaphones, forget massive pipes, and Super Traps, and then you track his ideal pipe sizes and see that there are very low back pressures with tiny pipes, which is not what we are told.
Nothing else comes into it at all. Heat and thermal gradient have a mild -/+ 5% bearing on ideal power at the intake, but possibly a major change of the ideal exhast length. The old motorbike trick of using enamel paint, and sawing it off where the paint stops burning is a very close to the ideal for peak power. I have no idea what happens when you thermal wrap it!
All of us have to think of the exhast system in the revers to the induction system. The primary inputs are Q= v.a. The heat factors influence power in small measure. A warm intkae is great first 5 minutes, a detonation hazard thereafter. People who block off heat stoves and EGR find the engines can often run better, but they are 3 to 5% ers, or 10% in really bad cases. The main influeces are that an intake needs a certain intake runner size realting to the intake valve, a certain volume 40 to 60% on non port on port engines, and certain heat gradient from the tip of the air snorkle or air filter, to the intake valve.
Over 125 years of engineering, Benz have gotten pretty darn good at working out what works!
The exhast reflects the health of the intake system, and is basically an anology with a gas turbine. The discharge co-efficent changes the net thrust (horsepower). By restricting it, it goes through a rob petter, give to paul deal in the torque and power. The heat factor does change the critical length of an out and out race exhasts, but I doubt it has nay bearing on a road car. Its gotta flow out back over the rear axle if its a sub 2 tone car to pass the feds.
The advice from Dick Johnston, Aussie race car driver, is that too often, exhast velocity is screwed up by a well meaning, but wrong, approach to reduce back pressure. Torque suffers as a result
The critical inputs of just the pipes are
Q, the flow in CFM, (You must have good CFM flow at 25"Hg for the mufflers, its is critical).
v, the peak velocity, and
a, the area.
The total volume,
surface area and
cross sectional area to each cube of engine is very important too, but the engine programs give guidlines for race engines, not streeters.
These all govern back pressure
A big single will always do better for maximum power than a smaller set of duals. But low and mid range torque can die if the gases are not extracted quickly, and the tone of the engine suffers in day to day use, becoming trumbone like and tending to reverberate. Check out a ricer with a big gun exhasts on a four cylinder engine. Deeper and more like a Model A. At the dizy heights of the power curve, a reduction of backpressure with the right fuel mixtures always raises power. Always.
As said, Ford and Holden in Aussie always use singles now on the sixes, but the V-8's run dual set-ups. The reason is the sixes are cheaper, and the eights are the image makers for each company. The thermal loss due to having dual exhasts will be greater, but the sound energy is more restrained, and at a higher pitch with twin pipes. Thermal wrap will upset the designers cooling of the exhast valves, as 25% of energy is going out via the pipes. Valve seat resession, cooling due to guide area is now upset.
David Vizard has some most awesome flow figures in his Mini and Ford SOHC books. He nails back pressure as the be all an end all the performance. Then he goes head hunting reverse waves like some kinda dragon slayer brandishing a flow bench. He specifies ideal types of silencer, and rates them in terms of standing waves very comprehensively. Then he just says to heck with megaphones, forget massive pipes, and Super Traps, and then you track his ideal pipe sizes and see that there are very low back pressures with tiny pipes, which is not what we are told.
Nothing else comes into it at all. Heat and thermal gradient have a mild -/+ 5% bearing on ideal power at the intake, but possibly a major change of the ideal exhast length. The old motorbike trick of using enamel paint, and sawing it off where the paint stops burning is a very close to the ideal for peak power. I have no idea what happens when you thermal wrap it!
All of us have to think of the exhast system in the revers to the induction system. The primary inputs are Q= v.a. The heat factors influence power in small measure. A warm intkae is great first 5 minutes, a detonation hazard thereafter. People who block off heat stoves and EGR find the engines can often run better, but they are 3 to 5% ers, or 10% in really bad cases. The main influeces are that an intake needs a certain intake runner size realting to the intake valve, a certain volume 40 to 60% on non port on port engines, and certain heat gradient from the tip of the air snorkle or air filter, to the intake valve.
Over 125 years of engineering, Benz have gotten pretty darn good at working out what works!
The exhast reflects the health of the intake system, and is basically an anology with a gas turbine. The discharge co-efficent changes the net thrust (horsepower). By restricting it, it goes through a rob petter, give to paul deal in the torque and power. The heat factor does change the critical length of an out and out race exhasts, but I doubt it has nay bearing on a road car. Its gotta flow out back over the rear axle if its a sub 2 tone car to pass the feds.
The advice from Dick Johnston, Aussie race car driver, is that too often, exhast velocity is screwed up by a well meaning, but wrong, approach to reduce back pressure. Torque suffers as a result
