[Ptero]

Back in the early 70s, I once came across an abandoned mining claim where the old timer had converted a straight 4-cylinder engine to obtain compressed air for his mine. I took a look at the plumbing and stared at it for the longest time, trying to make sense of it. He'd cut off the front of the exhaust manifold that collected the exhaust from the first two cylinders. And he'd brazed shut the hole to allow the remaining rear part of the manifold to carry away exhaust gas. He pulled the spark wires off the front two plugs and just left the plugs in. He'd taken the front part of the exhaust manifold, turned it around and brazed an iron pipe to the hole he'd cut in the manifold, and ran the pipe to an air tank! When he cranked it (it had a magneto), it fired on two cylinders and ran pretty good.

I describe this to illustrate that the internal combustion engine without combustion is an air compressor - and can be quite a good one if you delay the exhaust valve from opening until top dead center (TDC). The old timer couldn't figure out how to delay his valve so he got by on reduced compression.

Truck drivers, on the other hand, turn their diesel power plants into air compressors all the time. The Jake Brake shuts off the injector fuel flow and uses electric solenoids to delay the exhaust valve opening timing. By compressing air with the engine cylinders, you can slow down a 40-ton truck pretty good.

So forget about the easy fix myth for ecomodding engines by stopping the spark or fuel delivery. You gotta pull the piston. Otherwise you're running an air compressor - and that's not going to give you the mileage gain you're looking for.