ARGHHHHHH!!!!!!!!! Couldn't stay logged in to post. This is better?
I have driven LPG vehicles 10s of 1,000s of miles. I have converted several I've owned, and converted several for an LPG dealer I was working for at the time. Some have been switchable dual fuel, others straight LPG.
At one time the taxes on LPG were less per gallon than on gasoline. That was a pretty good incentive right there to drive on the cheaper fuel. Everyone is correct in saying that LPG has less BTUs in it.
I did overhaul a 350 cu. inch Chevy engine to set it up more properly for the use of LPG.
I upped the compression ratio and installed a longer duration camshaft.
After the overhaul the pickup had better power and got greater fuel mileage per gallon on LPG than it did on gasoline. Ten for LPG, eight for gasoline. I used Century brand carburetion whenever I could. The boss preferred IMPCO as he could get it at cost. I don't know if either is still sold or manufactured.
I have never converted an auto, only trucks and pickups.
Some states still have incentives for LPG vehicles, but only if they are purchased new. Others may have incentives for conversions, but I am not aware of them.
If you proceed with the conversion, remember to size your tank for LPG capacity, not water gallon capacity. A tank cannot be filled 100% full because of safety factors.
I'll try briefly to give some general conversion info for duel fuel.
An LPG carburetor is bolted down in place of the air cleaner, via the former air cleaner bolt.
The gasoline fuel line in cut and a solenoid activated cut off switch is installed.
An LPG regulator/vaporizer is mounted as close to the LPG carburetor as it can be. A vapor carrying hose runs from it to the LPG carburator.
The LPG regulator has an incoming fuel solenoid cut off similar to, but different than the gasoline cut off one. Prior to this is a fuel filter, then the line leads back to the LPG tank for connection.
The LPG regulator cools rapidly as LPG fuel is brought through it, so it need a means of keeping it warmed enough to vaporize the fuel. The vehicle cab heater water lines are cut and tees are inserted. From one of the tees a water line goes to the regulator bringing hot water to it. A return water line goes to the other tee. (Sometimes the tees are omitted and just one line is cut rather than both. This forces all heater fluid through the regulator and would somewhat restrict flow to the heater.
On most set ups a "Boden wire" leads from the LPG carburator to the dash of the vehicle. When a fuel switching occurrs the Boden wire is either pushed or pulled, and a plate inside of the LPG carburator is lifted or dropped depending upon which fuel you are going to and from.
The fuel solenoids are activated from a single post double throw (SPDT) switch on the dash. When switching fuels, you move the switch to the off position and let the remainder of the fuel burn out before switching to the other fuel.
This is probably more than you sought, but hope it helps in some manner.
Oh, there are a variety of tank configerations for vehicles. As an example, there are tanks that fit under the side rails of a pickup just above the fenders. This allows most conventional hauling instead of taking up bed space.
