I did a swap on my bronco, it's pretty easy. I could probably give you a hand this weekend if you need
edit: the swap basically goes like this:
1. Remove gas carb.
2. Install propane carb, install linkages.
3. Mount the vaporizer (cylinder looking dealie)
4. Run a propane line from the back of the carb to the fitting on the vaproizer.
5. Cut the heater line on the truck
6. Splice the heater lines into the vaporizer
7. Mount propane tank in back of truck
8. Run propane line from tank to vaporizer.
9. If you have one, install a lockoff between the tank and the vaporizer.
Pros: Since I swapped to propane I have never had my engine stall out on me. It's a bit of a hard starter on a cold morning, but it goes strong all day. It's also somewhat cheaper than gas, although that can change depending on where you get it. It burns cleaner although depending on how it's tuned the exhaust can smell of propane. Tuning is fairly easy since there are few moving parts and fewer adjsutments. There is minimal wiring needed and no computers or sensors.
Cons: The tanks are heavy and bulky, and cost more. The tanks can be harder to find filling locations and trail runs require more advance planning. On my setup at light throttle applications the intake whistles and is fairly annoying. I minimized that by using a closed air cleaner. On the street I noticed that I seemed to go through propane faster than I recall going through gas on the same distance trip.
Rumors: You're supposed to lose power going from a carb to propane, but since propane is more altitude independent and tghe fuel is a constant flow I found that I actually gained a little bit of power. I'm not good at tuning gas carbs though so your results may vary. You'd most likely see a loss going from fuel injection to propane and unless you absolutely hate electronics I don't see a point in doing that. Also, propane is supposed to make your motor run a little cooler since you splice your heat line into the vaporizer and the flowing gas cools the radiator fluid. I don't know how much of a difference it makes.
My opinion: Great for a trail rig without fuel injection. Forklift tanks are easy to find and hook up as are propane conversion kits. I prefer having a tow rig both to carry extra tanks and reduce the amount used for street driving. While you might be down on power some it's a near guarantee that your motor will run until it runs out of air, oil, or propane. I run it, I love it, and i'd do it again in a heartbeat. I won't run a carb on a trail again
Disclaimer: I am by no means an expert at propane conversions, but I did stay at a holiday inn express last night :thumb:
At the ranch we lived on in Montana all of the trucks were set up dual fuel. So they could run on propane or gas. With a TBI 454 Chevy as the test mule here is what we found. Propane provided a lot more power pulling. Propane provided less mileage than gas. Typically we'd get 8mpg on propane and 11/12 mpg on gasoline. However, at that time even with the decrease in mileage it was cheaper to run propane than it was to run gasoline. Propane for the ranch use was .68/gallon and for on the road use was 1.06/gallon. Gas was running 1.38/1.43 back then. Fueling up was never a problem as we had a 2000 gallon tank on the ranch and there was a 100 gallon propane tank mounted in the bed of the pickup. As far as I know, those trucks are still running around the ranch. They don't go out on the highway anymore as they've been replaced by Dodge Cummins. Not sure what the math was to switch over but I can imagine the accountants figured out some reason to switch.
I have the Impco 425 set up as well. I would never ever even consider going back to a carb! If a rig came with EFI I would leave it, but other than that, propane all the way. We will see how it works on a big block, I don't think the 425 mixer will be up to feed a motor that is over 500 HP. Also don't forget that if you build a motor for propane it actually makes more power than gas. Propane has an octane ating of 110-115 depending on where you get it from. Which means you can build a 12:1 12.5:1 compression motor and not have to run race gas!