LPG conversion

[Happy_Camper]

Yes, LP does give less energy than gasoline pound for pound of fuel. Stoich of gasoline is 14.7:1, and for LPG it's 15.6:1, plus as you said the BTUs are less. It's also a cold fuel, and removes heat energy. Running 11.5:1 compression will help regain some of the lost power and heat, but will not outperform a gasoline engine.
That said, it's very clean, so oil contamination is low providing better lubricity over the life span of the oil. Spark plugs run cleaner, providing better spark, Seal life is increased, so for the maintenance challenged individual, it's really great!
To get the best performance, the engine needs to be mechanically optimized for LPG.
I've pulled 13,000# equipment trailers with a 390 built for LPG in a '73 Ford F350, and the same trailer with a 390 built for gasoline in a '75 Ford F350. The gasoline truck had more usable power, and better fuel mileage, but was raucous compared to the smooth and quiet LPG truck.

[willowbilly3]

I have a whole system and Jay Storerer's out of print book that anyone interested should have.
What I can tell you I found out
Less power
Less mileage
Both by about 15% apparently
My is don't do dual fuel. If you are going propane then build the engine to optimize that system.

[rubiranch]

I built and tuned my engine for LP; I would never have a straight system because LP is not always readily available. That makes if difficult to leave the city.

[1969_Fords_Forever]

I've got a 1969 f100 with a 240 that runs on propane. However I run propane only no gasoline. I was able to use my stock 1 barrel carb. I just put a model E impco mixer on it with and adapter for a 1 barrel. The nice thaing about propane is it is great for long periods of idling or for drives around town. Basically it doesnt burn much fuel just sitting idle. You won't win any drag races with the propane 240, but once you get up to the highway speed limit it will cruise nicely and run very smooth. I don't think I will ever change mine back to gasoline.

[warponyxlt]

I heard it is hard on the valves but that is just what i heard

[Fordnatic]

It can pound the seats into the head-but if you have seats which work with unleaded it's ok for propane, too.