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I'm not sure if I understand this right, but is this supposed to increase the speed of the exhaust using a supercharger? If so, then that would be a blower, not a vacuum (same thing, I know, but it helps to make the idea easier to picture). A good idea in theory, but I'm not sure how much more power could be gained by compressing the exhaust to speed it up. |
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Seems to me like just adding multiple turbos (if huge power is your aim) would be more efficient and just as effective, since superchargers draw power directly from the engine like the alternator/generator and water pump; turbos make use of wasted power. Multiple turbos add more air and therefore more fuel, and so increase the exhaust output, increasing the exhaust's speed and spinning the turbos faster, making big power. |
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Reading all that in one hit has made my brain palpitate and my seat of consciousness wibble. |
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The number of variables in this system's operation are mind-boggling, but some quick basic figures (see ideal gas law) will show that the exhaust gases (usually 1450-1600F in the maximum horsepower and torque range) are roughly 3(+) times the volume of intake gases (*in a DRY state* neglecting the un-burned fuel particulate, which will increase actual volume exponentially).
'Normal' superchargers operate on positive displacement, and consume around 30% of pre-boost horsepower. Scavenging of exhaust gases with a positive displacement device will likely consume an amount approaching the engine's net horsepower, assuming the said device will hold up to the mechanical/tensile stresses created at such high volumes, which it probably will not.
It is much more efficient to deal with gas volumes at the intake side of the system, as is normally practiced. If one wishes to use the exhaust side of the system to increase performance, one should give it a higher volume capacity and resonant tuning... or use a turbo. |
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It's a differential pressure thing. It's easier to generate a higher positive intake pressure (cold charge) than extract very hot gases using a vacuum pump. Something like a Roots blower would be needed and the lubrication problems would be horrendous. If you used a centrifugal system (equivalent to driving power into a turbocharger turbine to make it extract) then you need a power source with very high rotational speeds which means complex gearing. |
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The thermodynamics are against this. It's probably bee tried; most major features of cars (turbos, superchargers, fuel injection etc.) had already been tried by 1920. |
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sucking the exhaust out of a car would create major
problems, especially after you took your foot off of the
accellerator, and you need a *little* resistance. C.O.M.E
performance engines reccomend the exhaust flow being
75% of the intake, that and there is *some* time where all
valves are shut anything sucking woult create a vacuum =
not good |
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I can do the same thing by smashing my exhaust system with a hammer. |
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This sort of negates the use of the heater, though... |
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Ok im gonna keep it simple since alot of people in here seams to like to play around with fancy words!
1: the increase in hp by sucking the exhaust out from the outlets by a supercharger that is either belt or electrically operated would steal as much horse power from the crankshaft as given in the reducement of pressure on the pistons not having to push it out, + some extra loss due to friction etc!
2: u will get no extra power mounting a turbo after the supercharger because the amount of gas and speed of it cant be increased since the only source of gas for the supercharger is what comes out from the engine. u will actually get less power out of the turbo cause the gases will have time to cool down and therefore lose some of its energy! |
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There's something called 'negative supercharging.'
Look here: http://www.impulsengine.com/
You increase the diameter of the exhaust pipe gradually all the way from the headers to the end... no turbo or pump needed. |
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It'd be better to create a powerfull resonating effect in the exhaust with a variable resonator that can work accross a rev range. This would complimient most tuned exhaust's existing ramming effect.
It would *technically* be using some of the exhausts energy to create a suction effect. You could gain around 10-40% less backpressure this way. I know some cars like hondas and lambroghinis have resonating exhausts (make a funny brassy booming sound). |
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Doing it mechanicly is near impossible. |
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Some amount back-pressure is necessary for producing torque at lower RPMs. That's why when I added a 2.5" dual exhaust to my Lincoln Mark 8, it lost torque from 0-25mph. However I also added 4.10:1 ratio positrac rear gearing and gained it all back and then some. |
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im not sure if resonance would be considered mechanical or not.. but this kind of exhaust is called a tuned pipe and yes it works for 4s engines, though not as efficient as with 2s |
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The GM blower people modify to use on cars is a scavenging blower for the exhause of two stroke diesels its been in action for ages buddy |
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or you could take your headers off and suck it out with your mouth |
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one big posative about this system is that as the exhaust velocity will be greatly increased, then during overlap the intake air velocity will be greatly increased and hence mor fuell hence more power |
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you would decrease the pressure in the cylinders ( vacuum ) and thus the intake runners. Inherently air blows thru better than sucking thru ( the same thing to a lot of people ) using the the available energy to blow instead of suck is more effective. pretty sure fuel has a better chance for staying in the mix when is is getting pushed instead of pulled |
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This has been tried before. Detroit diesel put superchargers on their exhaust manifolds during the 60's. Hot rodders took them off and used them on top of fuel dragsters as forced induction. I believe they were 8-71 superchargers. |
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Seems to me that a blower operating under these kinds of temperatures would lead to extremely high rates of wear, and hence abysmal life spans. And odds are they wouldn't be cheap. |
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errrr...sucking exhaust? I was led
to believe that turbo's used
residual energy in the exhaust flow
(but I may be wrong). |
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[Nza] is in the right track. Most
exhaust systems are woefully
inefficient but then have to cope
with wide rev ranges. If you are
tuning for a particualar power
band an exhaust system can be
designed to draw out the exhaust
using harmonics. |
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2-strokes use this as removal of
exhaust is very very important
seeing as they do not have a
separate exhaust stroke and must
scavenge the cylinder of exhaust
whilst filling it with fresh charge.
(this is one reason why valevless
2-strokes can have narrow or
peaky power bands and can be a
bugger to start). |
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Backpressure does help torque at low-speed and hurt high-speed horsepower. How about using an air-amplifier powered by CO2 in an exhaust sytem tuned for low-speed torque. Practical for drag racing only, once the exhaust begins to restrict high-speed horsepower, hit the switch and let the air amplifier increase the flow through the exhaust for a few seconds of high-revving trap speed. |
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I like the idea and me and my friend were thinking about
it before i read about it on this site its a good idea
because the supercharger would take care of a turbo's
lag and the turbo would take over for the high end power
that the supercharger has a harder time with due to its
limited by the engine by sucking out the exaust after the
turbo it would pull air through the turbo making it start
up and aid it through the rpm range. I'd just hate to be
behind the car with 8-10psi comming out the exaust pipe |
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I understand what your saying... How about in addition locating it on the very end of the exhaust pipe that would allow for cooling for the gas (probably only a couple hundred degrees at full throttle.) Using the head from Thomas Knights Turbo Electric supercharger ( SEE LINK ) would allow you to mount it way back there. To deal with the heat and the amount of flow have Knight make it with different gearing (this would lengthen spool up time of the supercharger head but net you the vac you wanted), spacers a heat shield and more spacers for the electric motors. Instead of using the compressor use the impeller side of a turbo. |
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I tried something like this on my 92 geo storm - with it at idle I could suck the exhaust all the way out of the garage using my shop vac (5 hp) but ANY throtle above idle caused the hose to the vac to blow off. By the time the exhaust got to the plastic hose it was plenty cool enough - remember this was at idle. |
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Any pressure over atmospheric in the exhaust as it meets the outside air represents wasted energy. Using a turbine or other means to help force air out of the pistons would waste more energy than it would save. |
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On the other hand, one idea I've sometimes thought would be interesting would be to use a trombone-style exhaust pipe to allow a wider range of well-tuned engine speeds (use a computer-controlled actuator to keep the pipe tuned to the engine speed). Not sure how it would work with a cat, though. |
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//"Backpressure does help torque at low-speed"// |
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So that means that if I weld a cap on my exhaust pipe I will have tons of torque because I have tons of back pressure |
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COOL I am going to go try it |
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I think that people are getting confused |
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So let me get this right ... according to this thread you can get more power by either reducing the pressure by sucking the exhaust gas out using a huge highly engineered air pump OR by doing nothing but sticking a potatoes up the pipe and increasing back pressure?? why do they even use an exhaust ... just weld the valves shut... |
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(knoe Kneed to edjukate mee - - I already understand the basics) |
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Basics of what? Being polite? <unnecessarily harsh> why do you bother speaking at all? Just weld your mouth shut </uh> |
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Sure there are scavenging blowers, but it's more hassle than the average consumer wants, having expensive high-speed parts whirling about in the corrosive atmosphere of their exhaust systems. Cheaper and easier to engineer a better static exhaust. BTW, the stock exhaust on your car (assuming it's not a performance-oriented car) is tuned more for sound than power. Aftermarket can help you. |
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Well, I was about to post a slight variation on this idea, but now I think I won't... evidently active exhaust pulling is not a good idea. |
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Ibelieve a French car in the 20s used something like this. They called it an exhaust expeller or something. I'm not sure. |
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in The Internal-Combustion Engine in Theory and Practice: Combustion, Fuels, Materials, Design
Charles F. Taylor (See All Contributors)
Paperback, 795 pages
MIT Press
March 19, 1985 or v-2 the crank driven scavenger is covered - I think for direct injection 2 stroke desel. |
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I've been considering a similar idea but I'm not an engineer nor even a mechanic, and I've noticed that ignorant minds think alike, too. |
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Say you forget the turbo and just run a pipe between a compressor run off a belt from the crank and an enlarged main exhaust pipe. Would you increase the exhaust velocity and/or HP? And if so, would those gains offset the parasitic drag from the compressor? |
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bmwr75r: is this anything like the "GM blower" you mentioned? |
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You could try cooling the exhaust before it enters the supercharger (or super-de-charger as it's for emptying not filling...). Presumably the cooling device would be called an "after cooler" and be something like a radiator or a water spray. |
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If done correctly, having a vacuum in the exhaust headers would suck the engine along, adding hp and making it free revving. |
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However, the super-de-charger would likely consume a HUGE amount of energy, requiring another engine just to turn it. To get around this problem, fixing a wind turbine to the car's roof could be a good way of providing power without an additional engine. |
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