Propane?
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Post Fiend
Joined: Jan 2006
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From: Kasson, Minnesota
Propane?
I'm getting a 521 stroker street motor built and considering using propane for fuel. The motor will be in a 77 F250 4x4. I know I will lose a bit of HP, but what is the average loss of HP using propane. What are some advantages and disadvantages for using propane for one of these motors?
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Joined: Mar 2006
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From: fargo, nd
im building a 545 to run on propane... still collecting parts for it though. if you build the engine to take advantage of propane's higher octane you wont lose any power over pump gasoline. mileage comes out about the same as well, but your engine will last a whole lot longer running propane because the oil stays clean... just be sure to get the best piston rings you can get because being a high compression engine it will have quite a bit of cylinder pressure, and oil control can be an issue too so id use standard tension oil rings. 11-1 compression with a mild cam is a good start, but if you go a big cam you could go to around 13-1 without issues... also youll need to run a 160 degree thermostat because otherwise the vaporizer and lockoff will gum up with crud. stoich a/f ratio is i think 15.5-1 vs 14.7-1 for gasoline, and running rich will make it run hot instead of like gasoline cooling down because its already a vapor. youll have to run either dual impco 425s or a single technocarb with 2 vaporizers to get enough flow for a 521. any other questions just ask 
Last edited by darrin1999; Mar 11, 2007 at 06:01 AM.
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Joined: Dec 2005
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I did a "propane rebuild" on the 460 in my '84 E350 motorhome last winter. It was converted to run solely on propane by the original owner but only went 85,000 Kms before needing some head work so I decided to do the bottom end as well. I replaced the dished pistons with flat top hypers to bump the CR to about 9.3:1. The exhaust seats in the original heads were just induction hardened so they didn't hold up too well to the higher temperatures.
There are quite a few issues to deal with when doing a propane build and the info is much harder to come by than with gasoline. On the upside though you can make an engine that will perform as well as any gasoline powered beast and it will never wear out (OK......never say never).
Compression ratio, ignition system/timing and high temp exhaust valves and seats are some of the things to focus attention on. Ask around your local engine shops about propane. If they stare at you like you sprouted a second head, look for advice elsewhere.
There are quite a few issues to deal with when doing a propane build and the info is much harder to come by than with gasoline. On the upside though you can make an engine that will perform as well as any gasoline powered beast and it will never wear out (OK......never say never).
Compression ratio, ignition system/timing and high temp exhaust valves and seats are some of the things to focus attention on. Ask around your local engine shops about propane. If they stare at you like you sprouted a second head, look for advice elsewhere.
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Joined: Jan 2006
Posts: 292
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From: Fort Worth,Texas
I didn't convert to propane but did find out about the weake exaust seats when I did some work on my heads. I went with Ferra stainless high temp valves and bumped the size 2.19 intake and 1.76 exaust. I had the shop install new hardend inserts on the exaust seats.
Bill
Bill
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