With Propane being "Made from" Natural Gas and crude I don't see many supply issues Unless Millions of vehicles were converted, As to pricing Its too high now (and changing Daily) as most suppliers (terminals, refiners) base the rack price (what the LP dealer pays) on the current crude price which is being artifically manipulated because its being treated as a commodity. So unfortunitly LP or Natural Gas may not be the best choice as an Alt fuel for a while.

 

Just a note, Propane is a part of raw natural gas that needs to be separated out. However, there is only a certain amount in there, and "making" more than that isn't common. Raw natural gas is made up of approximatly 1% Propane, and around 0.5% Butane.
So right now, propane and butane production volumes are pretty closely tied to the production of Natural gas.

 

Well propane burns hotter than gasoline so it does keep your engine very clean. My dodge 440 used to be on propane and it looked brand new when we took it apart. The only problem with this is it can be hard on exhaust valves. But they usually won't burn unless your pretty hard on the engine. And up in Canada, propane is usually half the cost of gas. I'm just getting out of college so I'm buying a 85 F-350 with a 460 on propane. Because a 460 has enough extra torque that the power loss of propane won't make much difference. And it will cost alot less to run.

 

Propane only burns marginally hotter than gasoline (3614°F vs 3591°F). It is only hard on exhaust valves when the engine hasn't been properly set-up or maintained. Propane burns with a different speed than gasoline so it needs its own advance curve. Potentially, the fuel mixture could still be burning when the exhaust valve opens if it's not timed properly or if the fuel mixture is set too rich.

I was just talking with the Ferrell Gas account manager in Buffalo, NY. The current price of propane motor fuel is $2.35/gallon with an account. Ferrell expects that you would buy at least about 1000 gallons/year to get that price. However, it makes more sense to lock in your price during the summer when the propane market is low. If you would have done that last summer, your price would been $1.95/gallon for this year. Not only that, the federal government is offering a $0.50/gallon tax credit for motor fuel so your price would (in effect) have been $1.45/gallon. Since propane has about 74% of the energy of gasoline, the equivalent price would be about $1.96/GGE, which would mean you'd be saving about $1.60/gallon today. The federal tax credit for propane isn't available for home heating use.

Injection conversions (like the ESIP Parts Package) have a minimal effect on power unlike the old Impco fumigation systems. They work a lot better on EFI engines and avoid intake manifold backfire issues.