While I was putting $100 worth of gas in my Bronco today, I started thinking about alternative fuels. I have been planning on a new engine for the Bronco early next year. I started by planning a 351 with some GT-40 heads and Holley fuel injection. Then I thought about propane. With gas prices on the rise again I measure mileage by the dollar instead of the gallon. My question is which engine would be best overall for this application? I want good power and better mileage. I like having V8 power but I want I6 economy. I know I can maintain power through gearing. So, what do you think would be my best bet, a 300 I6 or just keep the windsor? What mods could I do to either to make the most of the propane?  

Propane is basically the perfect motor fuel and is extremely clean burning (only pure hydrogen burns a little cleaner). Why some propane conversions do not "fly" is because they fail to exploit the true potential of Propane by using it on engines with lower compression ratios so they can "tolerate" 87 octane too. Propane has a octane of around 113 and does is magic best with CR's of 12 to 1 or better. Propane has less energy per gallon than gas but if you boost CR you should get MPG similar to gas on a lower CR engine (raising CR increases efficiency)and a lot more power too. I think a 300 six with high compression pistons running on propane would be a good project. Again to make the most of it you need to raise CR in engine well above "normal" to get the best propane has to offer as a motor fuel. Doing this will close the door to ever running 87 or 89 octane but you might be able to use a dual fuel setup with 93 octane and 11 to 1 CR or so.  

Cool, that's exactly what I was hoping to hear. The dual fuel idea sounds awesome. Thinking along those lines, how about running alcohol as a secondary fuel? There is a new ethanol and bio-diesel refinery in the works not too far from where I live. I doubt that they will mass produce any high octane but I know of a few locations locally to get alcohol or even nitromethane. I would prefer to keep it as simple as possible. It would be nice to pour a few $.79 bottles of alcohol in the tank to get me to a propane supplier in the event I run out. Then again I could carry a 20lb tank around for a reserve. I could even store propane around the house without the worry of it going bad. I could use some from my mother-in-laws 300lb house tank that she uses for winter heat. I could use the 2lb bottles for my lantern, they may be good for a mile or so. All these ideas make me wonder why more people don't make this conversion. Of course, that would increase demand and cost. I better keep quiet. LOL!  

A regular twenty pound bottle would not work as a reserve tank. You need a tank from a fork lift or such that is design to feed liquid fuel out of tank, not vapor because the rate at which vapor would have to be produced and drawn would freeze a 20 lb tank into a block of ice with little or no pressure in a few minutes at most. There is a heat exchanger with a propane system on a engine that converts liquid to gas before it is injected.  

Sounds like you are the guy to ask about a 1975 Bronco with a 1990 5.0 EFI HO motor conversion to a dual fuel conversion kit from www.technocarb.com ESIP injection kit and use my 12 gallon tank gas and a 40lb forklift tank in the bend of the truck.

I met a guy in 1996 from BC that had a custom 40gal tank and enjoyed cheap fuel.

What do you think.  $1800 plus a ($600)tank and mounts.  

I have a propane burner I drove for about a year on a 10.5-1cr 350sbc, it stank and had poor power and mileage. the tank took up two feet of the bed of the truck also, I took it all off and went back to gas. now it might be tolerable cause of the cost of fuel, I honestly hated it at the time.

I filled up the toy hauler a couple weeks ago and paid 2.70 something per gallon for the propane, if I remember right,... 150 bucks in gas for the bikes and 180 bucks in diesel in the burb to drag it to the china hat ohv area.  

You must have had something serious wrong with setup because because Propane can make more power that gas when setup properly, not less. UPS ran a propane powered fleet for many years switched from it when they apparently developed corrosion issues in aluminum head exhaust ports from high water vapor byproduct contents of of the fuel. (so I have heard anyway) My son is a assistant manager at a quick oil change place and they have a few fleet truck come in that are propane powered and drivers love them and say the run really well. When you change the oil in them it still looks pretty clean after several thousand miles too.  

I Also have a Bronco EFI 351 , i was kicking the idea of ethanol?
would like to hear your thoughts.