I think the whole propane=lower power thing is a result of implementation, not the properties of the fuel. By my calculations, you should at least make the same power, more likely more power, if the AFR is controlled as well as it was with gas, and the timing is maximized to run with the propane.
Propane, 21591 BTU/lb
Gasoline, 18400 BTU/lb
Stoich AFR
Propane, 15.7
Gasoline, 14.7
21591/15.7=1370.637 Btu/lb of stoich air:fuel mix
18400/14.7=1251.701 Btu/lb of stoich air:fuel mix
Propane certainly wins there. Other cosiderations, propane displaces air. Gasoline, when vaporized, does the same. But, gasoline is laregly injected as liquid into the cylinders. Which is a good thing if you think in absolute terms of oxygen getting into the cylinder, but a pretty bad thing for the quailty of the burn. Gasoline doesn't burn, gas VAPOR does. You have all these droplets, and the vapor around them burns. The end result is that not all the fuel gets burned. There is some left over. This is probably why gasoline makes most power far richer than stoich, even when it should in theory make max power when there is a perfect mix of oxygen and fuel. The extra fuel is needed, as some never finds any oxygen. With throttle injected propane vapor, you have a near perfect uniform mixture in the cylinder during combustion. The flame propagates through the mixture quickly and evenly. Max power is probably much closer to stoich.
Add to that almost perfect cold starting, without the need for lots of warm up enrichment (which is needed as a cold engine makes gasoline vaporization even poorer). Also consider the lack of any liquid fuel in the cylinder, no wash down on the cylinder walls, and oil that stays clean for 10,000 miles.
Propane rocks as a every day fuel.
I think I found the correct devise to control the vapor. A proportional control valve. I doubt it would work with any type of stock ECU, something with a programmable fuel map would be needed. A little electronic circuit to convert the injector signal into a fixed high frequency (>250hz) PWM signal. In my case, I'll probably have a duel inlet, single outlet solenoid before it, to cycle between propane and methanol. Injection point just before the throttle, with some sort of diffuser to aid methanol vaporization. BTW, the car will have no intercooler, so under boost when the methanol takes over, it's going to vaporize quite rapidly. The methanol tank will be a second propane cylinder, kept under pressure from the first, and draining out the bottom. Dual fuel systems through one control, requires only 1.5amps to run (vs 35A for low impedance injectors and a fuel pump), no pumps, single line to the front, quite nice. Certainly very KISS.
