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Self Supercharging engine 3

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CSLufkin

CSLufkin

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Feb 7, 2005
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Last night during a bench racing session, some friends and I discussed a concept that was new to us. I assume that it has been tried somewhere by someone (as almost everything has thanks to Smokey). Anyone please speak up, as this is probably tragically flawed.

There is a class that limits engines to four cylinders and forbids turbochargers and superchargers, but does not specify Natural Aspiration strictly. What if you took a V8 engine and used the exhaust charge from four cylinders to compress the intake charge for the other four cylinders? Let me explain a little more. It would have to be direct injected, the 'compressor' side would have no ignition, just air in, compression, and release compressed air thru a one way flow control of some sort into a chamber to be used in the intake charge of the other four cylinders. Understanding that there would be energy wasted in running the piston thru the power stroke without actually making power, do you think the power increase from the charged intake would overcome the power losses of swinging that heavier mass(8 cyl VS 4 cyl) and the wasted power stroke of the compressor side.
 
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I've worked on a few self super charging designs, everyone I've worked on required reed valves to push the energy balance towards positive, poppets are too complex, and waste energy.

There is a thread about SBC compressors, where half the motor is a compressor for air, while the other half powers it.


I dont think that normal head/piston/valve geometry is a very efficient way to compress things. There is way too much dead space at the top of the stroke. (You could modify the head to eliminate these problems.)

Interestring thought, though I dont know how well a SI motor would handle 2x the air from 0rpm till whenever the rpm's are too high for the whole second bank compressed intake air to move across.

Nick
I love materials science!
 
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The cam on the comperssor side would be 1 times rpm, so you would get 2 times the air. You would dome the piston for very little clearance. Sounds interesting.

There is a unit that kinda does this called GasJack from Compressco. The compressor side doen't seam to make enough air though when I looked at the curves.
 
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I think we also need to account for swept volume. In a conventional engine, where all 8 cylinders have the same swept volume (and are all tied to the same crank), using 4 cylinders won't give you any additional air per cylinder, if they feed the other 4 cylinders. To make this work as a supercharger, you would need the 4 "compressor" cylinders to have a larger swept volume per cylinder than the 4 that are used for making power. Then you would have a higher than atmospheric pressure in the power cylinders prior to their compression stroke.

Certainly not impossible, but not terribly practical, and absolutely not going to be allowed by any racing sactioning body in a "limited" class.

-Tony Staples
 
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It could be done, no special cam required, reed and or check valves. If i were the sanctioning body i would allow it no problem, convert as many cylinders as you like to supercharging so long as they all count towards the displacement limit. that being the case i suspect it would be a net loser. but i could be wrong ?
 
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It was done about 100 years ago on some early 20th century French racing cars. I forget the details.

It is a supercharger, so it would be illegal. A supercharger is a device to compress the inlet charge before it enters the cylinder.

Regards

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There has been rumor of people routing air through the bell housing to get some boost. The rumor said the Differential pressure was measurable. Put a couple holes into the top and route the positve pressure one to the air cleaner. A dividing plate between them may even help guide the air out bell housing.

I know were not about rumors here, but I thought the theory was interesting anyway.
 
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I think a reed valve compressor is a 2 stroke, so equal cylinders would pump about twice as much air as the 4 stroke consumes thereby giving near 15# boost, depending on the VEs of both sides.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
 
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Pat,

you are absolutely correct. I was assuming one stroke per each. If you added the reed valves, then you could get boost by using two pumps of the "compressor" cylinder, for each four stroke cycle. Then the problem becomes one of how to route air. To me, the smart option would be to use the "exhaust" valves as inlets for the compressor cylinders, letting the compressed air into the common intake via the normally "intake" valves.

Still, frightfull to implement, but fun to toss the idea around.

-Tony Staples
 
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Somewhat related:

While in its death throes, Triumph Motorcycles (the old one) came up with a piston having two skirts, the second much larger and attached at the bottom to the first. The engine was a twin, and the cylinders supercharged each other. There were, of course, two concentric cylinder surfaces for each cylinder, too. Given the extra complexity, the difficulty of making annular cylinders and annular pistons, and the difficulty of cooling and lubricating the combustion cylinder's walls, the idea probably didn't stand a chance, but it was a clever thing to have been exploring, in a company that was _not_ in dire financial straits. Given the company's business situation, I thought it was an irresponsible distraction, or maybe a last gasp.



Mike Halloran
Pembroke Pines, FL, USA
 
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Re: bellhousing supercharger.
In Smokey's three book series there is a brief description of a bellhousing supercharger. He said he welded fittings onto the housing, then filled it with expandable foam. When the engine was started it cleared a passage through the foam, and once the outlet was cleared of foam he claimed it produced positive pressure. My memory is foggy on how much it was able to produce or what sort of difference it made.

Thanks,
Jack
 
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Smokey claimed 22psi. dead headed at 6,000rpm. Did it make a difference? Look at the lap times of the 1962 Daytona 500 winner. Nobody else was even close.------Phil
 
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