Dear learned colleagues.....etc etc
A random thought popped into my head the other day regarding exhaust manifolds.
So, the cast ones are good because they retain heat better and that helps keep gas velocity up and the tubular ones are good because you can build them to purpose as far as torque and power needs apply.
Would there be anything to gain from building headers out of a heavy gauge pipe like schedule 40 which is a heavy wall tube?
All this assumes that the pipe is available with the correct radius bends and is also available in the suitable sizes, of course.
Oh, and there is a skilled, patient welder willing to do the work.
So, is it theoretically going to be of any benefit to an engine?
Manifold question
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Hi
If you are building a manifold for a turbo system then there is an advantage to building it out of heavy gauge pipe to keep the heat in the exhaust system, more energy in the gasses at the turbo. For a system in a normal car a heavy gauge system again is an advantage because it helps burn up any left over hydrocarbons and it keeps the noise down. For a more performance orientated set up then a better way to work is to make the system of thin gauge tubing because it heats up more quickly (races tend to be shorter than a drive to brighton) and keep the heat in with a ceramic coating, and they weigh less.
Best regards
Mike
If you are building a manifold for a turbo system then there is an advantage to building it out of heavy gauge pipe to keep the heat in the exhaust system, more energy in the gasses at the turbo. For a system in a normal car a heavy gauge system again is an advantage because it helps burn up any left over hydrocarbons and it keeps the noise down. For a more performance orientated set up then a better way to work is to make the system of thin gauge tubing because it heats up more quickly (races tend to be shorter than a drive to brighton) and keep the heat in with a ceramic coating, and they weigh less.
Best regards
Mike
poppet valves rule!
Retaining heat vs smoother flow kind of sounds like pure hogwash to me TBH?
Ceramics don't retain heat so if its just preventing the surface xfer I can only see the alternative having a really 'trick scientific' effect on surface friction at the gas/ metal boundary? How much would you have to cool the gas as a whole to affect its fluid characteristics?
Ceramics don't retain heat so if its just preventing the surface xfer I can only see the alternative having a really 'trick scientific' effect on surface friction at the gas/ metal boundary? How much would you have to cool the gas as a whole to affect its fluid characteristics?
Dave
Retaining heat vs smoother flow kind of sounds like pure hogwash to me TBH?
Sorry I don't quite follow here, heat is energy, a turbo charger is a heat engine, more heat at it's input more work can be done compressing the incomming charge for you, simples
"Ceramics don't retain heat" Yes they do they are an insulator, that is why you put them on as a coating they keep the heat in the exhaust charge. (I am not talking a pretty paint job on the outside, I am talking a funtional internal coating plus an outer coating to insulate the pipe from any cooling air).
"so if its just preventing the surface xfer" That is how they insulate!
"I can only see the alternative having a really 'trick scientific' effect on surface friction at the gas/ metal boundary?" You have lost me again here
"How much would you have to cool the gas as a whole to affect its fluid characteristics?" Temperature pressure and volume are all related to each other by the ideal gas law http://en.wikipedia.org/wiki/Ideal_gas_law double the temperature (absolute) you double the volume or pressure depending on wether it is a fixed volume or fixed pressure environment. Decrease the energy of the system you will reduce the velocity with which the exhaust charge moves toward the end of the tail pipe requiring a transfer of energy from any new charge entering the pipe, ie you will end up increasing back pressure (gas law above).
Best regards
Mike
Sorry I don't quite follow here, heat is energy, a turbo charger is a heat engine, more heat at it's input more work can be done compressing the incomming charge for you, simples
"Ceramics don't retain heat" Yes they do they are an insulator, that is why you put them on as a coating they keep the heat in the exhaust charge. (I am not talking a pretty paint job on the outside, I am talking a funtional internal coating plus an outer coating to insulate the pipe from any cooling air).
"so if its just preventing the surface xfer" That is how they insulate!
"I can only see the alternative having a really 'trick scientific' effect on surface friction at the gas/ metal boundary?" You have lost me again here
"How much would you have to cool the gas as a whole to affect its fluid characteristics?" Temperature pressure and volume are all related to each other by the ideal gas law http://en.wikipedia.org/wiki/Ideal_gas_law double the temperature (absolute) you double the volume or pressure depending on wether it is a fixed volume or fixed pressure environment. Decrease the energy of the system you will reduce the velocity with which the exhaust charge moves toward the end of the tail pipe requiring a transfer of energy from any new charge entering the pipe, ie you will end up increasing back pressure (gas law above).
Best regards
Mike
poppet valves rule!
Have you data that compares exhaust gas temp in a cast vs tubular manifold, its not like one is 0C and the other is 800C from what I've seen. 100C difference with horribly restricted casting is still going to be detrimental to a nicely flowed 'cold' tubular header.
..and I have had internally coated manifolds for over 7 years, so some experience. I don't think I'd ever claim that the internal coating did anything more positive than stop heat getting into the metalwork and being transferred back to the heads (conduction + convection & even radiation) TBH.
..and I have had internally coated manifolds for over 7 years, so some experience. I don't think I'd ever claim that the internal coating did anything more positive than stop heat getting into the metalwork and being transferred back to the heads (conduction + convection & even radiation) TBH.
Dave
Hi
There are many factors that effect manifold performance as you have pointed out, the major ones are pipe lengths, diamiters how tight bends are how good the joints are between sections, this was a question about 1 aspect, wall thickness, I have tried to answer in (relatively) simple terms about how/why this effects performance. Yes a badly designed cast manifold will be worse as a performance manifold than a tubular one, the temperature will be different, probably not by much in a short time frame but again it's coating will also contribute to the way it performs, otherwise why would ever bother to develope them? No I don't have figures ready to post, sorry life is too short, but if you want a good start on the subject a read of the manifolds section of maximum boost by Corky Bell, it also goes into why a thicker wall thickness on a turbo engine is good for throttle responce/ avoiding turbo lag, which you could actually work out from what has already been posted, and of couse there is also google, which is how I get alot of the material I read.
Best regards
Mike
There are many factors that effect manifold performance as you have pointed out, the major ones are pipe lengths, diamiters how tight bends are how good the joints are between sections, this was a question about 1 aspect, wall thickness, I have tried to answer in (relatively) simple terms about how/why this effects performance. Yes a badly designed cast manifold will be worse as a performance manifold than a tubular one, the temperature will be different, probably not by much in a short time frame but again it's coating will also contribute to the way it performs, otherwise why would ever bother to develope them? No I don't have figures ready to post, sorry life is too short, but if you want a good start on the subject a read of the manifolds section of maximum boost by Corky Bell, it also goes into why a thicker wall thickness on a turbo engine is good for throttle responce/ avoiding turbo lag, which you could actually work out from what has already been posted, and of couse there is also google, which is how I get alot of the material I read.
Best regards
Mike
poppet valves rule!
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Thanks, Mike! I was out buying some steel and saw a few pre-bent sections of really heavy walled pipe and it set me wondering if it may be worth all the effort to do or whether it was going to be minimally beneficial on a time/effort/results scale.
It would be for my own use on a street car, RV8, possibly turbo'd but probably not, as a daily driver. I have a decent welding setup that I want to put to good use and it seemed like a worthy challenge for a project.
It would be for my own use on a street car, RV8, possibly turbo'd but probably not, as a daily driver. I have a decent welding setup that I want to put to good use and it seemed like a worthy challenge for a project.
Cheers,
John
John
Hi
If you are going to fit turbos then yes it is well worth the extra weight, If you are planning on it in the future I would also get the Corky bell book he recommends some very ussefull pipe bends/ manifold tapers that enable you to make a collector in heavy gauge without having to cut up loads of pipe bends. If it is for a NA set up I would stick with 1/16" wall pipe it is much easier to work with.
Best regards
Mike
If you are going to fit turbos then yes it is well worth the extra weight, If you are planning on it in the future I would also get the Corky bell book he recommends some very ussefull pipe bends/ manifold tapers that enable you to make a collector in heavy gauge without having to cut up loads of pipe bends. If it is for a NA set up I would stick with 1/16" wall pipe it is much easier to work with.
Best regards
Mike
poppet valves rule!
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unstable load
- Top Dog
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- Top Dog
- Posts: 1285
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