Gas engine into air compressor

Discussion in 'Shop Talk' started by Siryet, Aug 6, 2005.

  1. Siryet

    Siryet In Remembrance

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    Does anyone know the basic procedure for turning an eight cylinder gas engine into a four cylinder air compressor?

    Thank you for your information
     
  2. agmantoo

    agmantoo agmantoo Supporter

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  3. farminghandyman

    farminghandyman Well-Known Member Supporter

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    we did it once and it was ok,

    we took the intake valves and put a very light spring on them so they would self open and then made the exhaust fixed, and used the spark plug hole and added a check valve on to it, the problem is the check valve is usually not designed for the heat that is a by product, compression,

    I heard that back in the 50' there was a company that would re-machine the head of a straight 6 and put air compressor valves in three of the cylinders, but I never found that company or more information, (my guess is that they used a flat head in that conversion,

    I don't know if the balancing of the firing of a V 8 is such to run it from one side of the motor or not, but if it is, I would think one may be able to buy commercial Air compressor valves and a plate of steel or aluminum, and have the valves machined to go in to the plate and replace the head of the motor with true air compressor valves,

    but it may just be cheaper to by a large air compressor head and drive it from a gas motor,
     
  4. Janon

    Janon 993cc Geo Metro

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    Be extremely carefull while experimenting. Obviously, a gasoline engine uses gasoline - and the last thing you want is a big tank filled with a compressed air/fuel mixture.

    I would think that a compressor could be made with having both the intake and exhaust valves for the "compressor cylinder(s)" completely sealed shut. Perhaps removing the push-rods and welding the valves closed. Also blocking the intake port for that cylinder in the manifold. Again, you DO NOT want any air fuel mixture going to those cylinders. All the "plumbing could be done through the spark plug hole via one-way valves (a pair per compressor cylinder - creating a two-stroke with only intake and compression). An 8cyl engine will run on only 6 or 7 cylinder, although it will obviously have a miss. If you were really creative, you could run the V8 as a V6 by modifying the firing order/distributor, or whatever (aren't some of the chev V6 engines actually the chev V8 engine just minus the two cylinders?).

    Be careful!
     
  5. moopups

    moopups In Remembrance

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    Trailer mounted commerical compressors are made from Ford 302 engines, one bank equiped to handle compressed air, the other bank supplies the internal combustion engine needs. A small version can be made by useing a Chrysler air conditioner from the 80's driven by a single cylinder gasoline engine. Go by a rental house and have a look under the cover to see how its done on a commerical unit. As far as purchasing the special equipment, that would have to come from a manufacturer or a talented tinker.
     
  6. DrippingSprings

    DrippingSprings In Remembrance

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    ive got one of the chrysler ac jobs i made for a work truck. you have to use the old style York compressor that has the oil reservoir. I can run anything from a impact to a paint sprayer off mine.
     
  7. WisJim

    WisJim Well-Known Member Supporter

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  8. Janon

    Janon 993cc Geo Metro

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    Lets just say a 350 cubic inch engine

    - 4 of 8 cylinders - 175 cubic inches
    - for every revolution of the engine = 175 cubic inches of air
    - 175 cubic inches = 1.22 cubic feet per revoluton
    - a 350 cubic inch engine idles at approx 700rpm
    - 1.22 cubic feet x 700 rpm = 854 cubic feet per minute
    - 1 cubic foot = 7.5 gallons
    - 854 cubic feet x 7.5 = 6405 gallons per minute = 107 gallons per second

    Perhaps my calculations are off (I've no idea what a V8 operating on 4 cyls would idle at), but that sounds like alot of compressed air.

    cheers,
     
  9. moopups

    moopups In Remembrance

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    A cubic foot of air features 1728 cubic inches, that is where the formula goes off track. 12 x 12 x 12 = 1728 cu. in. Each revolution would be about 1/10th of a cubic foot.
     
  10. John Hill

    John Hill Grand Master

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    I did some asking around friends who have tried such things and this is what I learned.

    The challenge with converting an engine to be a compressor is the volume of the combustion chamber.

    As the piston comes up it compresses the air into the small space whereas ideally it should push all that air past a non return valve.

    The usual result is the some of the air is compressed but stays in the combustion camber and expands while the piston goes down but it would be better if the piston was drawing more fresh air in.

    So, not as much air as one might think is drawn in and not as much compressed air as one would like is pushed into the air receiver tank.

    This lost efficiency costs fuel and and is wasted as heat.

    If you dont care about the losses then all you have to do is replace the valve springs with really light springs that open under atmospheric pressure and put a non-return valve in the spark plug hole, cam followers, push rods etc are removed. Both valves become inlet valves. But you can only run at low revs because of the slow action of the valve springs, to run faster you need to change the camshaft so that both valves are open on the down stroke and closed on the up stroke.

    One guy suggested that if you fitted a turbo charger fixed for max boost (i.e. waste gate fixed shut, and feeding the compressor cylinders only you would overcome some of the problesm. At about this stage another round of beers arrived and the discussion switched to simply fitting the biggest turbo charger you can find in the scrap yard and using the output of that direct.
     
  11. Janon

    Janon 993cc Geo Metro

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    Exactly right you are (I was wondering what anyone could possible do with that much compressed air).

    350 cubic inch engine running 4 cylinders as compressors would theoretically produce about 500 gallons per minute of compressed air.

    cheers,
     
  12. John Hill

    John Hill Grand Master

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    But Janon the theory goes off track because of the air that remains in the combustion chamber and this air expands on the down stroke reducing the amount of new air drawn in.

    If the combustion chamber is 1/10 of the total volume. i.e. 10:1 compression ratio once the air receiver pressure got close to 150 psi no more air would be compressed. That would be because atmospheric air is about 15 psi so 150 psi is the maximum pressure that particular engine could produce. All that would be happening is the air in the cylinder would be getting squeezed then expanded again on every revolution.


    I guess you really need an engine with an infinitely high compression ratio!
     
  13. agmantoo

    agmantoo agmantoo Supporter

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    The efficiency is greatly reduced in using a gas engine design since the piston has to make a complete cycle in order to make compressed air. Example, if the piston is at TDC then it must travel downward to bring air in then travel back to TDC to expell. A quality industrial design machine would compress air on the crank side of the piston downstroke and expel compressed air at the bottom of the down cycle. The top of the piston would have sucked air in on the same stroke to be expelled as the piston returns to TDC and the lower side of the piston would have sucked in air at the same time. The machines that can do this have 4 sets of valves, positioned with an intake and exhaust on both sides of the piston (top and bottom) whereas the auto engine will only have valves on the top side of the piston.
     
  14. Siryet

    Siryet In Remembrance

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    WOW. Thank you all for the information. Will be pondering this. :cool:
     
  15. Janon

    Janon 993cc Geo Metro

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    No doubt there would be lots of difficulties and "gotchas" when attempting to actually build something like a 4 cyl air compressor out of a V8 engine. It would certainly be fun to experiment with.

    cheers,
     
  16. ozarks58

    ozarks58 Member

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    Schramm used a piston Comp. on it's popular T64 well drill rig until 1977. It was made using the engine block of a truck engine. 6 cyl and water cooled. A 318 Detroit Diesel powered it at 1800 RPM. It all started with a super charger blowing air into the first 4 cylinders. That air was putup to over 100 psi. It went to a cooler that looked like a radiator with a fan to blow air thru it. From there it went into the 2 remaining cylinders and was boosted to 250 to 300 psi. Expensive stuff. Just the Switzer super charger is around $5000 for a rebuilt one. Just thought I'd toss in what can be done with an engine block and money. 425 cfm at 250 psi