Converting your gas powered rig to propane power.

By Lance Clifford and Vince Howdyshell (aka: Hank Hill)

Here is my propane tank. It sits perfectly between my fenderwells.

This is the fuel lock. It allows fuel to enter the vaporizor. It is activated by engine vaccum. I have it mounted on the inside of the firewall.

Here is the vaporizor-regulator. It's job is to regulate the high pressure tank LPG down to low pressure vapor. Notice the heater coolant lines running through it.

Here is the air/fuel mixer (caburetor) and air cleaner assembly. Notice the large hose going into the top of the air cleaner. This is the actual fuel line into the carburetor.

Here is a shot of the throttle linkage. It was the same as my quadrajet carb. Notice the leftover manifold burrtio from a previous trail run. ;)

Here is the filler cap where you add propane to the tank. I put it in a nice and accessible area. I decided not to put it in the stock location, because I often grind boulders across that region. ;)
So why on Earth would someone want to run propane in their vehicle, when it runs just fine with good old fashioned gasoline? Well, I had several reasons for doing it. 

First off, my carburetor needed rebuilding. My gas tank was pretty shot, so I needed a new fuel tank. Not to mention gas prices were nearing $2.00 a gallon. When a friend of mine asked me if I wanted to convert my rig over to propane from a wrecked one ton truck that he had, I was all over it. So with a little reaserching, I dove into it head first. It turns out it was a simple conversion, that anyone can do. 

Here are the pros and cons to think about, before making a desicion to go propane:


  • It burns much cleaner than gas. No carbon buildup inside your engine. After 5,000 miles, your oil will still look new! 
  • It is MUCH cheaper than gas. As of today, fuel at the corner gas station is $1.69 a gallon. Propane is about $1.10 at the same station. Down the road a little farther, it can be had for $0.89 a gallon! 
  • A propane powered vehicle will run at almost ANY angle. It will run better than a fuel injected vehicle at an extreme angle, because the fuel injected vehicle will die shortly after the fuel pickup in the tank looses fuel. The propane vehicle will run much longer thanks to being a pressurized system. It does however have a fuel pick up at the bottom of the tank, so eventually it will quit running.
  • A propane system is very simple. Virtually no moving parts, and no computer/electroics to mess with, like fuel injection. No fuel pump, even 
  • A 103 "pump" octane rating


  • Propane is not as readily available as gas, although due to the increase in recreation of all types propane is fast becoming more readily avalible everywhere. 
  • If you live in extremely cold environments (10 degrees F or below) you may need a block heater. 
  • Not everyone runs propane, so you better have enough fuel! 
  • You need to learn how to tune it, since no one else will know how to! 

    There are 4 basic parts to a propane system. 

    1) The tank(pressure vessel). You want a good, NEW tank,or one with no rust pitts deeper than.025" .The tank MUST be ASME approved with the clover stamp clearly visible and have the following: a pressure relief valve,filler valve,bleeder valve(liquid level gauge), a manual shutoff valve,and a fuel level gauge(visual) along with a vapor outlet and a liquid outlet. Automotive propane tanks are very heavy duty, since  tank pressures vary from 40 to as high as 275 psig, depending on ambiant/fuel temp.

    2) The Fuel Lock: These valves operate by vacuum, engine oil pressure or electrical solenoid. 

    3) The Vaporizer/Regulator: Also called a converter this little bugger converts high pressure liquid propane into low pressure vapor.

    4) The Air/Fuel Mixer: This is a very simple carburetor that mixes air and fuel into the engine. There are three basic types: air valve mixer,the venturi principal mixer,and the mechanical metering mixer. 

    Of course you will also need fuel line to run from the tank to the fuel lock as well. You need to use triple steel braided line that can easily handle the high pressure, minimum 250 psi. Also a must is a Hydrostatic Relief valve in line between  any shut-off valves. 

    Where can you find all of these things? The easiest place is your local propane supplier. Places like Amerigas, or Suburban Propane can supply you with all new parts needed for the conversion. For everything new, you are looking at about $800. Or you can find the stuff used. I got all of my stuff from a friend's wrecked propane truck for free. :) The first step is figuring out where and how to mount your tank. Now remember, this tank is pressurized, at about 200psi. You really want to make sure it's in a protected area, and safe from rocks. If you are going to mount it underneath your rig, build a very stout skid plate for it! For ease of installation and for safety's sake, I decided to mount it inside the vehicle. For added piece of mind, it was securely mounted completely to the vehicle's roll cage. The tank has a Excess Flow valve built into the liquid line valve. This will automatically  stop the flow of fuel should a sudden burst in a line occur. 

    Now that you have the tank mounted, you can begin mounting the fuel lock and the regulator/ vaporizor. You want these to be as close as possible to the carburetor. I mounted mine on the firewall. The vaporizor needs to have your heater hoses plumbed into it. The heat from the coolant keeps the propane nice and warm. If you didn't run coolant through the vaporizor, it would freeze up after a few minutes. You should also have the regulator mounted right next to the vaporizor. Once you have the regulator and vaporizor mounted securely, you can run the high pressure line from the tank to the regulator. Be sure to route it so that it is out of harms way. Keep it away from the exhaust, and away from rocks! 

    Now that you have the tank, fuel lock and the vaporizor/ regulaor hooked up and mounted, you can install the carburetor. For me, this was a simple swap out. My propane carb matched my previous quadrajet exactly, so I simply removed the old Carburetor, and bolted the propane carb on. The linkage hooked up the same too. No need for a choke anymore, either. :)

    All that's needed to connect the vaporizor to the carburetor is some fuel filler line (see photo). Again, make this line as short as possible, due to the low pressure. 

    Now that you have everything hooked up, you can remove some of your old stuff. You no longer need your gas tank (duh). You also need to remove your fuel pump, if you have a mechanical one. If you don't want to make a plate to cover the hole, you can leave the fuel pump in place. However, you should remove the push rod that goes from the cam to the pump, since the pump will no longer need to pump. :)

    Now you are ready to fire it up, assuming you have propane in the tank. If not, trailer it over to the local gas station, and sit back while they fill up your rig for you. Yep, you get free full service. 

    You are now ready to fire it up, and see what happens. When I finished installing my setup for the first time, it was about 20*F and snowing. I turned the key, and it immediately fired up. It idled prefectly smooth, like it had been warmed up for an hour before hand. I was very impressed.

    After getting everything setup the way you want, it is recommended that you take your vehicle to a shop that specializes in propane systems for fine tuning. Once again, your local propane supplier should be able to refer you to someone.

    Here are some technical specs for LPG:
    Chemical formula:
    Specific gravity:
    Liquid: .509
    Vapor: 1.52
    Weight per gallon:
    4.24 lbs.
    Boiling point (atmospheric):
    Heat Value:
    per cubic foot (vapor): 2516 BTU
    per pound (liquid): 21,591 BTU
    per gallon (liquid): 91,547 BTU
    Ignition temperature:
    Maximum flame temperature:
    Flammibility limits:

    Upper: 9.60%
    Lower: 2.15%

    Ideal combustion ratio:
    By weight: 15.5:1
    By volume: 24:1
    Cubic feet of vapor:
    per gallon: 36.4 cu. ft.
    per pound: 8.6 cu. ft.
    Octane ratings:
    Research: 110
    Pump: 103
    Vapor pressures:
    Pressure (psi)