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blazerbrad · 09-08-2011, 08:43 AM

78Buford switched from a carb to propane a couple of years ago on his F-250 with a moderately built 469 (desktop dyno estimates 340 HP/525 FT-LB on the carb...take it for what it's worth but that is the best guess). The truck is probably 5,500-6,000 lbs. with 1-tons, 42" Swampers, and a C6/205/4.10 axle gear combo so not much gearing at all. He lost some top end power but the low end and throttle response are much better, but he contributes that from going from an almost 800 cfm 4-barrel carb to a 425 cfm mixer. However I did ride with him during a mud bog this last Memorial Day and the engine was able to spin the 42's through pretty thick mud around 5,000 rpm the entire 200' pit, so that is some pretty good wheel speed (about 1/3 the trucks got stuck, including a Super Duty on 38's with a wicked diesel).

He is very happy with the setup and has no plans to ever switch back after a couple of years of running propane. He has stated that in hindsight he would have built the engine with a higher compression rate and went straight to propane to begin with.

On a typical trailride he gets into the 2nd tank on the first day. We spent 2 days in Slade/Red River Gorge running all over on Booth's property one day and the "public" area (Sandlick) the next, so quite a few pavement miles also. Believe he was still on the 3rd tank at the end of the second day but it was close to empty. He carries 4 tanks on the truck all the time (he tends to be a little excessive on this, and has plenty of room) and another 2 in the tow rig. Granted, you can't count on having the tanks refilled when out of town so that is a concern, but has never been a problem.

Regarding this statement from Carwash:

"It only runs at about 85% the efficiency of gasoline. So it takes you 10 gallons of pane to get you what 8.5 gallons of gas does. This also means that a 300hp motor becomes a 245hp motor, etc."

This is only partially true. Technically propane has less energy content (BTU's) than gasoline so "efficiency" is not really accurate. You need to use more propane to equal the same power content as gasoline. So yes, the example of using 10 gallons of propane to equal 8.5 gallons of gasoline is accurate BUT the horsepower of the engine should remain equal regardless of fuel. The 300hp with gas but only 245hp with propane is only accurate if the fuel rate is identical (use 8.5 gal. of gas and only 8.5 gal. of propane)....increase the equivalent fuel rate when going to propane and you get the power back.

09-08-2011, 08:43 AM	#11
blazerbrad - CORE Member - Join Date: Feb 2007 Posts: 831	78Buford switched from a carb to propane a couple of years ago on his F-250 with a moderately built 469 (desktop dyno estimates 340 HP/525 FT-LB on the carb...take it for what it's worth but that is the best guess). The truck is probably 5,500-6,000 lbs. with 1-tons, 42" Swampers, and a C6/205/4.10 axle gear combo so not much gearing at all. He lost some top end power but the low end and throttle response are much better, but he contributes that from going from an almost 800 cfm 4-barrel carb to a 425 cfm mixer. However I did ride with him during a mud bog this last Memorial Day and the engine was able to spin the 42's through pretty thick mud around 5,000 rpm the entire 200' pit, so that is some pretty good wheel speed (about 1/3 the trucks got stuck, including a Super Duty on 38's with a wicked diesel). He is very happy with the setup and has no plans to ever switch back after a couple of years of running propane. He has stated that in hindsight he would have built the engine with a higher compression rate and went straight to propane to begin with. On a typical trailride he gets into the 2nd tank on the first day. We spent 2 days in Slade/Red River Gorge running all over on Booth's property one day and the "public" area (Sandlick) the next, so quite a few pavement miles also. Believe he was still on the 3rd tank at the end of the second day but it was close to empty. He carries 4 tanks on the truck all the time (he tends to be a little excessive on this, and has plenty of room) and another 2 in the tow rig. Granted, you can't count on having the tanks refilled when out of town so that is a concern, but has never been a problem. Regarding this statement from Carwash: "It only runs at about 85% the efficiency of gasoline. So it takes you 10 gallons of pane to get you what 8.5 gallons of gas does. This also means that a 300hp motor becomes a 245hp motor, etc." This is only partially true. Technically propane has less energy content (BTU's) than gasoline so "efficiency" is not really accurate. You need to use more propane to equal the same power content as gasoline. So yes, the example of using 10 gallons of propane to equal 8.5 gallons of gasoline is accurate BUT the horsepower of the engine should remain equal regardless of fuel. The 300hp with gas but only 245hp with propane is only accurate if the fuel rate is identical (use 8.5 gal. of gas and only 8.5 gal. of propane)....increase the equivalent fuel rate when going to propane and you get the power back.