I don't think you need to do anything to the engine to run it on propane or natural gas. I converted a car in 1990 to run on natural gas. It was very successful. There was a slight loss of power because the natural gas doesn't produce the same BTU's as gasoline so I was told. The following is something I found on the internet which says basically the same thing. I realise you have said you want to get the 'most' out of the propane but I think it's not worth tearing down your engine to modify it.
Cheers George
OK, so what's involved in making an engine run on propane?
Basically, instead of delivering vaporized gasoline as the engine sucks in the air/fuel mixture during the "intake" cycle, the engine delivers propane/air mixture. The engine itself is not modified in any way. It still sucks in the air/fuel mixture, compresses it, ignites it and converts the resulting explosion (internal combustion) into rotary energy during the power stroke. Thus delivering work energy to the item which requires power (to rotate a generator armature for example).
The waste products are still expelled in the exhaust stroke, and the process continues, over and over. It's like using little controlled explosions to rotate the output shaft. Suck it in, compress it until it's explosive, blow it up, and use the explosive energy to rotate the output shaft. That's the way an engine works!
OK, enough said... It's really that basic. A propane conversion just swaps one kind of fuel for another, and the other principals are the same.
