crazy idea, home-made air compressor?

[pjtoledo]

it's 2 AM, the brain is getting a bit wonky, and I'm coming up with the crazy idea to convert a 3.0L into an air compressor. the engine is already an air pump right? it sounds reasonable that we could modify it to make a self-contained gas powered air compressor.

the plan seems easy; use a fuel injected engine so 2 cylinders can be "turned off", then make some headers that divert the "non-exhaust" of those 2 cylinders to a tank. not needing all 4 strokes anymore you can add an extra lobe on the affected valves to create a 2 stroke on those cylinders. add lobes to open the intake valve on the power stroke, and the exhaust valve on compression strokes. of course deleting overlap would be necessary.


doing the math, a 3L engine with the center 2 cylinders converted should pump out 70 CFM at atmospheric pressure while running at 2000 RPMs. pumping losses would cut that back some, lets settle for 50 CFM at 2000 RPMs actual.


cranking compression is in the vicinity of 135+, so it should easily build usable pressure.

I'm not sure how to calculate the air flow at a useable 90 PSI.
comparing it to my existing 2hp that puts out 7.4 CFM at 90 while turning the compressor at an estimated 500-600 RPMs it would seem that larger cylinders at triple the RPMs should provide some decent flow.

what do you all think?? start welding cams & headers? or man-up and buy a real compressor?

side note, the only task I need more air for is sandblasting. my 40+ year old Montgomery Ward 2hp unit is still adequate for tools and tires.

(using 2hp for sandblasting is comparable to using dial-up for the internet)

 

[JamesH]

Get welding... It sounds like you have a lot figured out. Draw the plans and build it.

Sent from my Moto Z (2) using Tapatalk

 

[JoshT]

Too bad Gwaii isn't still around. He had a home made compressor built using a 2.8L or 2.9L. Can't recall if he used the gas engine to pump like you are talking about, or if it was driving a separate air pump.

 

[91stranger]

Sounds like a lot of work and constant problem solving to get it right. I would just weld up a secondary tank that's at least 40-50 gallons. If you have a good pump and motor then a larger tank is all you would need to be happy. Can normally find a lot of bad air compressors that leak or bad motors for cheap.

 

[RonD]

No fancy plumbing of exhaust is needed just put one way valve in the spark plug hole and you will get about 120psi on running engine compression stroke.
Stick spark plug back in and drive it away


You can also re-purpose AC compressors, you do need to add an oiling system, which can be done with PCV system on the engine

 

[pjtoledo]

Sounds like a lot of work and constant problem solving to get it right. I would just weld up a secondary tank that's at least 40-50 gallons. If you have a good pump and motor then a larger tank is all you would need to be happy. Can normally find a lot of bad air compressors that leak or bad motors for cheap.

yes, it does sound like a lot of work. but this is exactly what us 'ol retired guys do: pick the hardest way to do something, then perfect the process

 

[adsm08]

Do what you were planning, but run the engine off bank 1 and do your compressor side off blank 2. Just disable those fuel injectors.

It should run off only three cylinders since it has almost no load, and that should give you near constant air supply, as the firing switches banks every time, so for each hit you should get a cylinder worth of air.

 

[Curious Hound]

Doesn't a "jake brake" basically do that with a diesel to provide engine braking for the vehicle?

 

[RonD]

Yes, diesel and 2 stroke engines can make use of compression release engine braking
Compression is released(on compression stroke) and then one way valve closes on "power stroke" so it slows pistons downward motion because a vacuum is created above piston

But to get and keep pressure you want to release it into a pressure tank, so just use spark plug hole

 

[adsm08]

But to get and keep pressure you want to release it into a pressure tank, so just use spark plug hole

You would need a good check valve though if using a tank, or else you will end up pulling your air back into the cylinder each time a piston goes down.

 

[91stranger]

How and where will all this be mounted? Are you making a mobile stand so you can move it around the garage or will it be stationary? Still seems like waaayyy to much work for an air compressor. But you do you boo boo and let us know how it goes.

 

[RonD]

I would use two valves on the one spark plug hole

One used as check valve on the pressure tank line to prevent backflow, then another valve in Reverse with an air filter that allowed air to be sucked back in on "power stroke" so no drag on engine, like with a compression brake.

Using the exhaust port would eliminate valve to a point I think you would still want something to prevent pressure loss.

And you could use BOTH, then two "compression strokes" during the 4 strokes.

But I like the spark plug source because it can be used "in the vehicle" with minimal tools and tooling for "on the road" needs, then you can put spark plug back in and drive away

 

[alwaysFlOoReD]

Well now I want to build one....I have a couple spare 4.0l.
I have to wait till I have my own place, damn.

 

[adsm08]

I would use two valves on the one spark plug hole

One used as check valve on the pressure tank line to prevent backflow, then another valve in Reverse with an air filter that allowed air to be sucked back in on "power stroke" so no drag on engine, like with a compression brake.

Using the exhaust port would eliminate valve to a point I think you would still want something to prevent pressure loss.

And you could use BOTH, then two "compression strokes" during the 4 strokes.

But I like the spark plug source because it can be used "in the vehicle" with minimal tools and tooling for "on the road" needs, then you can put spark plug back in and drive away

I was building this in my head as something where the engine is not in a vehicle, but out on a stand of some sort.

Also, I think I would use three cylinders for compressing air, have a check at each spark plug and one on the tank. If you use a pushrod engine it is a simple matter to disable the exhaust valve to get two compression strokes per revolution if using the spark plug hole for your feed to the tank.

 

[RonD]

Yes, that would work but you would have to have the two valves on the spark plug hole or there would be no "air" in the cylinder on exhaust stroke.

Intake valve only opens on the one Intake stroke sucking air in, then pushes air out spark plug hole on compression stroke
If air couldn't get back in on Power Stroke then there would be no pressure to push out on exhaust stroke.

And with the two valves on the spark plug hole you could disable both cylinder valves intake and exhaust, lol