OK...Back Pressure Shoot out! One and for all!
01-09-2004, 05:05 PM
#61
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Justin, outstanding technical reply, as always.
As for the 5" performance loss you mentioned, I recall there was considerable differences between people's responses as to whether or not they saw a difference some said good, others bad, others no change at all. But as you alluded to, it doesn’t make much sense to go terribly larger than the turbine outlet really. Don’t get me wrong, I only have a 4" setup single stack and if I recall Loretta Mitchell has a 4" single stack on her red truck and we all now the type of power its making. I would say 5" pipes on an HX35 are not at all necessary by any means. That backpressure is always bad, I meant it and will stand by that. It’s always bad, period. But that didn’t imply that I felt that there would be measurably less back pressure on a 5" piped truck that has say an HX35 compared to a 4" piped truck. I doubt you could read that difference on a 0 to 10" H20 manometer. But any restriction placed in the exhaust for the soul purpose of 'creating' a velocity increase at the expense of backpressure, such as a special muffler or a ridiculous "turbine vane device" (don't want to quote product names for fear of greedy lawyers) is positively absurd and marketing ploys at their finest.
The fact that our exhausts are pulsed impacts the flow modeling tremendously, no doubt. As far as the turbo 'seeing' these pulses, the design of the exhaust manifold becomes critical.
No argument whatsoever about the gasses cooling down and increasing in density thus creating restriction as they go down the pipe. That’s why I am a staunch supporter of fully insulated exhausts.
Your four items for the perfect exhaust I agree with totally, with one possible addition, if you wanted to get really fancy and make it 'perfect' I would say you would want a gradual taper from the turbine outlet, the entire length of the exhaust system, so that as the gasses cooled and became more dense you gave the gasses a larger and larger area to pass through. Once again, its much easier to just keep the gasses as hot as possible in the first place.
With regards the exhaust of the B1's, HX 40's etc. I would have to say that more important than the actual diameter of the exhaust spool piece of the housing is the effective area of outlet created by the blades of the turbine. For example, one turbo may have a 4" dia. outlet, which is 12.6 in^2 of area, but only 10 in^2 area of turbine blade open area for exhaust. It would indeed be interesting to see the comparisons between flow area of the turbine and outlet size for the different turbos.
Zino
As for the 5" performance loss you mentioned, I recall there was considerable differences between people's responses as to whether or not they saw a difference some said good, others bad, others no change at all. But as you alluded to, it doesn’t make much sense to go terribly larger than the turbine outlet really. Don’t get me wrong, I only have a 4" setup single stack and if I recall Loretta Mitchell has a 4" single stack on her red truck and we all now the type of power its making. I would say 5" pipes on an HX35 are not at all necessary by any means. That backpressure is always bad, I meant it and will stand by that. It’s always bad, period. But that didn’t imply that I felt that there would be measurably less back pressure on a 5" piped truck that has say an HX35 compared to a 4" piped truck. I doubt you could read that difference on a 0 to 10" H20 manometer. But any restriction placed in the exhaust for the soul purpose of 'creating' a velocity increase at the expense of backpressure, such as a special muffler or a ridiculous "turbine vane device" (don't want to quote product names for fear of greedy lawyers) is positively absurd and marketing ploys at their finest.
The fact that our exhausts are pulsed impacts the flow modeling tremendously, no doubt. As far as the turbo 'seeing' these pulses, the design of the exhaust manifold becomes critical.
No argument whatsoever about the gasses cooling down and increasing in density thus creating restriction as they go down the pipe. That’s why I am a staunch supporter of fully insulated exhausts.
Your four items for the perfect exhaust I agree with totally, with one possible addition, if you wanted to get really fancy and make it 'perfect' I would say you would want a gradual taper from the turbine outlet, the entire length of the exhaust system, so that as the gasses cooled and became more dense you gave the gasses a larger and larger area to pass through. Once again, its much easier to just keep the gasses as hot as possible in the first place.
With regards the exhaust of the B1's, HX 40's etc. I would have to say that more important than the actual diameter of the exhaust spool piece of the housing is the effective area of outlet created by the blades of the turbine. For example, one turbo may have a 4" dia. outlet, which is 12.6 in^2 of area, but only 10 in^2 area of turbine blade open area for exhaust. It would indeed be interesting to see the comparisons between flow area of the turbine and outlet size for the different turbos.
Zino
01-09-2004, 09:26 PM
#62
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OK for an uneducated question... Would a turbo outlet sized down pipe expanding into a pair of 4 or 5 inch stacks be detrimental to performance? Stacks on a road truck are not absolutely necessary but is very beneficial for safety reasons. What would be the best way to accomplish this? Would one stack be better than two?
01-10-2004, 09:49 AM
#63
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Haulin, I dont think that would be a problem at all. Just make the transition from the 3.5 to the 4" or 5" fairly gradual. personally, I would recommend the single 4" stack. Its less work, and all you need really. just depends on wheter or not you really want the look of duals.
Zino
Zino
01-12-2004, 11:04 AM
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HID-- I might be dense, but could you please elaborate on the safety aspect of stacks?
Z-- I think I understand more now where you are coming from. I will grant you that backpressure at all is bad in a pure sense. I think you would agree that on a stock engine, increasing to a 6" exhaust will likely accomplish no good (over a 4"). The idea being that the "decrease" in backpressure is so marginal (going from almost none to almost none), so insignificant, that it is outweighed by the cooling effect of the larger pipe. Thus, stagnation of flow and poor performance.
When I upgrade to an ATS manifold, I WILL have it thermal barrier coated inside and out. Then I can get closer to adiabatic Carnot efficiencies. I would be willing to be that a coated manifold would help turbo spooling SUBSTANTIALLY. Especially since the ATS manifold is a little heavier, thus serving as a heat sink.
I actually thought about including a slight taper from turbo to end in my "ideal" system. I was thinking about how many motorcycle exhausts are done, with a constant, steady taper to the end, like a megaphone. Maybe I should put on a Meg's tip?
Too bad I am broke and don't own a dyno, nor have the time to dyno test one exhaust setup vs another. But even those companies that DO have the money and facilities to dyno often disagree on results! What's a guy to do?
Right now, I am looking at the Dodgezilla hybrid-- there are guys runniing up to 500hp on it, with great spool up (though it probably shouldn't go past 450 like any other HX40 compressor).
Maybe I will get the downpipe coated as well!
It's time to get coating-happy!
Z-- I think I understand more now where you are coming from. I will grant you that backpressure at all is bad in a pure sense. I think you would agree that on a stock engine, increasing to a 6" exhaust will likely accomplish no good (over a 4"). The idea being that the "decrease" in backpressure is so marginal (going from almost none to almost none), so insignificant, that it is outweighed by the cooling effect of the larger pipe. Thus, stagnation of flow and poor performance.
When I upgrade to an ATS manifold, I WILL have it thermal barrier coated inside and out. Then I can get closer to adiabatic Carnot efficiencies. I would be willing to be that a coated manifold would help turbo spooling SUBSTANTIALLY. Especially since the ATS manifold is a little heavier, thus serving as a heat sink.
I actually thought about including a slight taper from turbo to end in my "ideal" system. I was thinking about how many motorcycle exhausts are done, with a constant, steady taper to the end, like a megaphone. Maybe I should put on a Meg's tip?
Too bad I am broke and don't own a dyno, nor have the time to dyno test one exhaust setup vs another. But even those companies that DO have the money and facilities to dyno often disagree on results! What's a guy to do?
Right now, I am looking at the Dodgezilla hybrid-- there are guys runniing up to 500hp on it, with great spool up (though it probably shouldn't go past 450 like any other HX40 compressor).
Maybe I will get the downpipe coated as well!
It's time to get coating-happy!
01-12-2004, 04:26 PM
#65
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There is no doubt in my mind that coating the manifold inside and out will greatly improve turbo response. The coating helps greatly, but is only mills thick, so the R value is not terribly high. Consider also isulating (dont get to see the pretty ATS manifold though) the manifold and turbine housing with a high temperature blanket such as Kaowool. Then make it pretty again with some lagging. As for the down pipe, use cerawool or kaowool based pipe insulation, 1" wall thickness and lag it as well and seal the ends to keep the water out. Obviously there are places along the run where the pipe will be too close to some obstruction so you wont be able to insulated it there, but I am sure you could insulate 90% of the surface area. Get that done and see the turbo response!!!!
Of course your broke... Youre an engineer !!!! lol
Zino
Of course your broke... Youre an engineer !!!! lol
Zino
01-12-2004, 05:37 PM
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What about the underhood blankets from places like Geno's Garage? I think that would be a nice addition to the Thermal barrier coating.
I am trying to remember the name of that coatings company that was in a Popular Hot Rodding magazine last year. Maybe it will come to me.. I was really impressed with their work.
Btw-- I am not an engineer, I just play one on the DTR
I am actually a Poli Sci major, but a guy who loves engineering and the hard sciences.
Justin
I am trying to remember the name of that coatings company that was in a Popular Hot Rodding magazine last year. Maybe it will come to me.. I was really impressed with their work.
Btw-- I am not an engineer, I just play one on the DTR
I am actually a Poli Sci major, but a guy who loves engineering and the hard sciences.Justin
01-12-2004, 06:48 PM
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The two companies I use on my drag car are Jet-Hot and Airborne coatings.
Uh, Oh. ....Poly Sci.. Amazing, my career is your hobby interest, and your career is one of my hobby interests..... Want to start a discussion on the conspiracy theory of the establishments' role in the sinking of the Lusitania (to get us into WWI) and the 'surprise' attack on Pear Harbor (to get us into WWII) that FDR knew about, not to mention the Council on Foreign Relations being a front for the elitist banking establishments and their desire for one-world government..... oh boy I better stop.. this is more than just slightly off topic........
Zino
Uh, Oh. ....Poly Sci.. Amazing, my career is your hobby interest, and your career is one of my hobby interests..... Want to start a discussion on the conspiracy theory of the establishments' role in the sinking of the Lusitania (to get us into WWI) and the 'surprise' attack on Pear Harbor (to get us into WWII) that FDR knew about, not to mention the Council on Foreign Relations being a front for the elitist banking establishments and their desire for one-world government..... oh boy I better stop.. this is more than just slightly off topic........
Zino
01-13-2004, 08:49 AM
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SWAIN TECH!!! I finally remembered it! I KNEW it was buried in that cranium of mine somewhere.
I have seen a lot of coating work (jet-hot, HPC etc) and I haven't seen anything that equals the quality of the swain tech coatings.
Justin
I have seen a lot of coating work (jet-hot, HPC etc) and I haven't seen anything that equals the quality of the swain tech coatings.
Justin
06-23-2005, 01:21 AM
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just my research and personal experience... i believe the less back pressure the better. i dont really want to get into 5000 words why so i will show you a link instead that i would say explains it. http://www.thedieselstop.com/content...20Banks%20Chat
scroll down a little its around the top. from gale banks himself its about the 23rd line i think... i figured it was worth checking out. again im just going by my experience and this little bit of research. im going to go to wyotech and study diesel technology in a bit and ill swing it by them and see what they think too. i think all that you have said makes sense though so its kinda one of those things you just gotta try for yourself and hope for the best.
scroll down a little its around the top. from gale banks himself its about the 23rd line i think... i figured it was worth checking out. again im just going by my experience and this little bit of research. im going to go to wyotech and study diesel technology in a bit and ill swing it by them and see what they think too. i think all that you have said makes sense though so its kinda one of those things you just gotta try for yourself and hope for the best.
06-24-2005, 05:30 AM
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My head really hurts after this
.
So would this be the actual physics behind how I used to tune my go-carts exhaust as a kid? By putting a 2 foot long pipe on as the exhaust and running the crap pout of it to get it hot, then cutting the pipe at the point where it changed colors?
Im a simple person and like simple answers
.So would this be the actual physics behind how I used to tune my go-carts exhaust as a kid? By putting a 2 foot long pipe on as the exhaust and running the crap pout of it to get it hot, then cutting the pipe at the point where it changed colors?
Im a simple person and like simple answers
06-24-2005, 08:37 AM
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So if gasses cool so rapidly in the pipe and thus loose velocity wouldn't a person benefit greatly to have a large dia. pipe dump behind the cab. Especially because most of the tight bends on our trucks are located at the rear end of the exhaust system. Seems that it would still be very hot at or near the rear of the cab and would flow a lot better.
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