Without a lot of other modifications, running LP gas is a giant leap backwards. The first result is around a 5% or greater reduction in power from the gas displacing some of the air voume that would normally be drawn into the carburetor. This can be offset to some extent by taking advantage of the approximate 110 octane of LP gas and raising the compression ratio of the engine to 11:1 or so. You'll also need stellite exhaust valve seats and/or stainless steel exhaust valves, so by the time you amortize the cost of building an engine that can never be run on gasoline, even in an emergency, and being restricted to areas where LP gas with road tax added to the price of the fuel is available, the engine will be worn out. To my decidedly biased point of view, that's a fool's mission.
"Propane" is a misnomer. LP (Liqufied Petroleum) gas is a mixture of Propane and Butane, and the blend is altered seasonally. Butane produces more thermal energy than Propane, but it "freezes" (stays liquid) at 32 degrees F. Propane evaporates at -70 degrees F. or so, and winter mix gas has a higher volume of Propane mixed in for easier evaporation. That doesn't matter much for cooking or home heating, or powering your back yard hot dog grill, but it makes a big difference in engine performance. "Your mileage may vary", but I choose to deal in facts, not fairy tales!
Jerry
