Convert wounded GM 6.0 into a compressor?

[strantor]

I want a whisper quiet high volume, high pressure air compressor. Something like this or a pair of these. Since it's just a want, not a need, I can't justify spending the money (nor do I even have the money). And since I like building things, I thought maybe I would make one.

Before I go further, let me clarify: I want to turn an automobile engine into a piston air compressor. Yes it can be done; there are examples all across the internet. Yes I know it will require modifications to the valves, et. al. And I want to turn the whole engine into a compressor (electric driven); not the monoblock 4 combustion cylinders/4 compression gas-powered compressor scheme.

I have a 2005 Yukon Denali in my driveway with a blown 6.0 V8 engine; threw a rod through the side of the block. By my (probably bad) math, if the other 7 cylinders are intact, then I should be able to get 25cfm @ 150psi out of it right around 1385rpm. By my (probably bad) logic, if a GM V8 engine idling high around the target RPM is quiet enough to carry on a conversation beside it while there are >5500 explosions per minute occurring inside, then it should be totally possible (possibly by reusing/reconfiguring the donor vehicle's intake & exhaust components) to make the resulting compressor equally or more quiet in the absence of those explosions.

My reason for posting is, I've never had enough time or curiosity to dissect a lost cause engine for science and rate the damage to the other cylinders on a 1-10 scale, nor do I know anyone else who has either. Has anyone here? What are the odds that the other cylinders are good? I suppose a compression test would tell me, but before I can do that, I'll have to at minimum drop the oil pan and clear the shrapnel from around the crank, and I don't even know if it's worth the time. Could I do it without rotating the engine? Could I just hook an air line to each cylinder one at a time from the little 1hp compressor I've already got, inflate it to max PSI, block it off, and see if it bleeds down?


Also I've never built a compressor from an engine, and I know at least one person on this forum has, and I'm curious how far off base I am about the pressure, flow, RPM figures and the noise level.

 

[strantor]

If I sound like a raving madman, here's some of the information I've been ingesting which led to my insanity.

PTO Driven Car Engine Air Compressor - Part 1 - zeketheantiquefreak - YouTube

PTO Driven Car Engine Air Compressor - Part 2 - Running - zeketheantiquefreak - YouTube

FARM SHOW Magazine - The BEST stories about Made-It-Myself Shop Inventions, Farming and Gardening Tips, Time-saving Tricks & the Best Farm Shop Hacks, DIY Farm Projects, Tips on Boosting your farm income, time-saving farming advice, farming tractors

https://www.tractorbynet.com/forums/build-yourself/108519-homemade-air-compressor.html

Successful use of air compressor in a wind turbine

 

[shovelmike]

Being a gearhead, such ideas have occurred to me as well. After clearing debris from the crankcase you would need to modify a connecting rod, fixing the lower section and bearing on the journal of the cylinder that threw the rod so that the oil pump can build pressure to keep things lubricated. Main thing with the valvetrain would be to drive the cam at 1 to 1 ratio with the crankshaft to eliminate the unneeded compression stroke. I see in one of your linked videos how the individual converted to two stroke in another fashion, interesting ingenuity.
Achievable, but I am not sure I would bother except to satisfy my curiosity. Let us know how it works out.

 

[texasranger556]

That would take a pretty serious electric motor. Do you have something already available?

 

[MossRoad]

If you threw a rod through the block, that means there's a hole in the block. You're going to have to contain the oil in the bottom end of the engine, so you'll have to plug the hole, or you'll be hemorrhaging oil all over the place.

Also, the engine is now out of balance since one cylinder is gone. How are you going to get it back in balance? Stuff like that I'd be thinking about before investing any money. Your time is free (if you don't put a value on your time) so tear into it and see how badly things are jacked up in the bottom end. Then remove the heads and check the top ends of the cylinders.

 

[strantor]

Being a gearhead, such ideas have occurred to me as well. After clearing debris from the crankcase you would need to modify a connecting rod, fixing the lower section and bearing on the journal of the cylinder that threw the rod so that the oil pump can build pressure to keep things lubricated.

Thanks, I hadn't considered that.

 

[strantor]

That would take a pretty serious electric motor. Do you have something already available?

Right now I have a 5hp motor I could put on it for proof of concept. Geared down to where it could turn the crank, it would (assuming the whole concept isn't fatally flawed) put out the air at the pressure I want, but CFM would be way shy of target. From there I can upgrade to the 15/20HP motor this demands, and i can get a used one cheap or free in my line of work, just haven't had cause to lug one home until now.

 

[4570Man]

If you had it patched up enough to work you could probably run it on 4 cylinders. Why not just use the 4-4 or in this case 4-3 compression idea. I think an electric driven v8 would be a horribly inefficient. If you go that approach I think you’d be better off to remove the cam shaft, close all the valves and put a check valve in the spark plug hole. It can suck air in and every stroke is a compression stroke. You could take it a step farther and trade the heads for a flat plate which would increase the compression ratio and increase the air pumped per stroke. You could probably find an old industrial compressor and be off to a lot better start. I’m not sure how you’d go about calculating the CFM. It’s not as simple as a liter to CF conversion times rpm divided by compression strokes. The problem is due to compression it’s not moving 6 liters per compression stroke on every cylinder.

 

[4570Man]

The more that I think about it modifying the heads to close the headspace to pretty much zero would be a must do otherwise you’re wasting most of the compressed air.

 

[Warpspeed]

If you study normal air compressors design, they don't use a cylinder head as such, but a "valve plate". Its a much simpler way to go about it than trying to modify an internal combustion engine and its original poppet valve train.

A valve plate is just a flat sheet of metal bolted directly to the top of the cylinder block, there is no large combustion chamber space, its just a flat steel plate. You could bore two holes into that plate for the intake and exhaust valves. Both valves are just flat reed valves, or something very thin and flexible and springy. The exhaust valve is just a springy flap that sits on top of the valve plate. As the piston comes up, air forces the flap valve open.
As there is zero combustion chamber volume, its VERY efficient at pumping all of the the air out, especially against the high constant back pressure that a compressor normally has.

The intake is a similar thing, but the flapper valve is mounted flush under the valve plate, and opens by itself as the piston moves down the bore. Its all very easy to make, especially if you buy proper reed valve replacement parts for an existing commercial air compressor. Trying to do something clever with the original cylinder head and camshaft is still a lot of work, and its never going to work as efficiently.
In this picture the exhaust flapper is on top surrounded by an orange O ring. The five upper holes feed the intake flapper located underneath (that you cannot see).

An alternative arrangement that has several advantages is to place the intake reed valve on the top surface of the piston crown. As the piston moves down, inertia tends to help open the intake valve, as well as air pressure. As the piston goes back up, inertia helps slam the reed valve shut. The induction air all must come through the crankcase, which is not a problem.

The top of the valve plate then just has only the exhaust valves. Its then a lot easier to fabricate a sealed box over the whole valve plate as a combined exhaust manifold.
This picture shows a very small air compressor with the induction reed valve placed on top of the piston, which is quite a common design.
It would be very easy to do with an automotive piston, especially if its slightly dished.

If you go about it this way, it will be vastly more efficient than trying to use an original cylinder head with a large combustion space. So much more efficient, that the compressor can be run at greatly reduced rpm (but at a higher drive torque). But the lower drive speed will definitely help with noise.