A piston engine is an air pump. Perhaps you could take a well worn one that is worn eveny and add spark plugs and a carburator. I don't know how you would mount the distributor though. In the end you would be cheaper to just buy a good used engine even if it were a gasser.

The old 5.7 olds diesels were so similar to the gas engines you could bolt on gasser heads pull the injection pump and install a distributor there and run them as gassers using the stock diesel cams. I hear they put out a lot of power too.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

That's interesting. The reason why you'd want to do this is because dedicated 96% ethanol 4% water engines in Brazil have high compression at 19:1 or so, which a diesel has. I think these engines are more efficient than gas or diesel. I was reading about some researchers that did a study for the EPA that converted a jetta TDI in this way, adding spark plugs and a distributor for idle and low speeds but it would diesel at higher speeds. So I guess it would be a spark and compression ignition engine. They got 22% better fuel efficiency than diesel from alcohol, more power, and the thermal efficiency was 43% with half of the exhaust gas recirculating into the manifold. Also very low emissions. Not sure if you'd need a carb, it says they used a lower pressure fuel pump from a gasser and had the fuel go into the heated manifold. Also they lowered the compression to 18:1. I think the idea is to de-compress but not by as much as a standard gasser which is less efficient on alcohol than gas. I bet it'd sound super smooth, should be much cooler and less vibration.