Gasoline to LPG conversion in a 250???!!!



Ive been readin som of the posts from our ozzy and kiwi freinds about ford sixes runnin on propane. My question is how do you convert a 250 to LPG? How much sense does this make in the US because of availability? Id also like a little feedback on throwin turbos on a LP engine

thanks all
8) all you really need, after the proper fuel tank and pump, is a propane carb. the conversion is simple and has been done on several different engines. propane with a turbo is a good way to go as propane has a higher octane rating than gasoline does. while availability is somewhat limited, compared to gas, you can find propane fairly easily. i know of at least one station in tucson that sells propane, and i have seen many stations along the route i take to shenandoah that sell it also.
Slv49, I am building up a turbo-LPG 250. The engine's at the machine shop right now, but I am excited about how it should run. I got it all real cheap, too. I paid $25 for a good used turbo out of a local salvage yard (from a Buick turbo 231), and about $100 for a complete LPG setup off a Chevy 350 on eBay (minus tank which wouldn't fit my 66 Mustang anyway).

I plan a draw-through configuration. If you think about it, this makes sense, since all aftermarket LPG systems sold in the US through the late 90's are draw through. A draw-though turbo also perfectly mixes the propane with the incoming air, assuring an even mixture to each cylinder (which never occurs with gasoline).

There are a couple of things to keep in mind, though. First, the advance curve is different for LPG than gasoline. LPG needs a faster rise, but less total timing than gasoline. Also, even though LPG has a higher octane number than gasoline, it lacks the evaporative cooling effect of liquid fuels, so you can't really raise the compression ratio much above what a gasoline engine will stand.

On the flip side, turbocharging and late-model, low compression engines ('78 and on, IIRC) go hand in hand for making great torque and power. To harness all that thrust, I rebuilt a C-4 from a stout 302 to fit behind the 250, but am keeping my 2.83:1 8" rear end (at least until it breaks! ;)). A low numbered rear end "loads" the engine, which helps build heat and pressure in the exhaust system for spooling up the turbo quickly.

This car is a long-term project with lots of development still to be done, but I have enough turbo and high performance experience to be confident in the outcome.

Here are a couple of web sites you should be sure to save offline for extensive study and inspiration. The first web site highlights a recent Ak Miller turbo-LPG project: ... illys.html

This one looks at some of the subtle technical issues to keep in mind with turbos (not an LPG project, though):
Things to think about>-----Well this has really piqued my interest. I think i wanna do it but im lackin on the specifics. Is there somwhere i can find out more detail how to do this or mebbe one of yall could tell me more. Also where are kits obtainable. (couldn find nothin on ebay)
No, there are no turbo-LPG kits available. The LPG kit I bought was not a turbo kit, but rather a normally aspirated kit for a Chevy 350. I chose this size because I wanted to get from my I-6 250 about what I could expect from a SBC for power and torque. All the components I bought (turbo and LPG kit) are properly sized to do that. (BTW, it took me the better part of a year to find and buy the right kit on eBay. They don't come along every day.)

I am going to have to fabricate everything I need to match the exhaust manifold to the tubo, the LPG mixer (carb) to the turbo, and the turbo to the intake log. As well as bracing for the turbo, exhaust pipe, throttle linkage, LPG tank installation, LPG fuel lines, etc. Then once I have it running, I'll probably need to do a lots of tuning to get it all working together, as I am cobbling together bits and pieces that were never meant to work together.

But that's what I do. Why buy it when you can spend less money to build it yourself, educating yourself along the way, and keep the tools for your next project when you're done...? ;)

And I really can't explain everything in detail, either. There are a couple of good books on turbocharging that you can buy at nearly any bookstore, and there's plenty of discussion in these threads. Search on the terms "turbo lpg" and you should get lots of hits.
Just to clear it up so I wont look ignorant, i wasnt talking about turbo lpg kits, just plain lpg conversion kits. thanks for all the info 54, it really helps
What about a GRA TB, angled over the valve cover? I know this would make tappet adjustment a chore, but it might just about clear under the "lid", and be a good candidate for retrofit intercooled turbo. Or you could lie it on side, feeding in from the front of the log with a milled or fabbed or cast right angle adaptor.

Or steal Steve's (buickroadster) idea and use a fabbed plenum with three (progressive) throttle bodies off small carbs below it. A kind of DIY Offy.

Just some ideas for ya.

Cheers, Adam.
FWIW, I am using a IMPCO kit, Slv49. IMPCO are the largest supplier of kits in the US, and parts are cheap and plentiful. Any local LPG suplier or gas utility can help you find a supplier in your local area. Just look them up in the Yellow Pages and give them a call.

Also, be sure to read the "original" on-line DIY guide to LPG conversions. Tom Jennings wrote a book on DIY LPG conversions about 15 years ago, and recently made it available free of charge on the internet. You can download it at

This is a very complete work that's aimed squarely at the home mechanic. Good luck! :)
:) with blowen/turbo lpgas systmes we run the compression at about 10:1!! with 5-10 lb of pinging problems if you keep the total advance at 30(2500rpm)and the initial(idle)advance to 10-15 degrees.agood lpgas curve is the same as a petrol curve ,that any good tune up shop can do."o" ring the head when it is off too,it helps stop blowing them steve 8)
Point well taken, Steve. With the right engine components and preparation, one could do all the things you list. But with the turd-head American 250's, with their sh*t casting quality, I think one is safer to start at low compression and inch one's way towards greater power than to go straight for max effect and risk blowing it up.

Same with timing. One sees all manner of suggested curves, but generally, I've noticed that they seem to recommend a couple of degrees more advance at idle, a fast rise, and a couple of degrees less advance above 3000 RPM -- not too different to what you write. In the event, my point to Slv49 is that making it all work right is going to take some effort and experimentation. It is not a "bolt on" kit that one can assemble and expect to have running perfectly in an afternoon.
:) Yeah i know bout our sixes. There aint nothin that is bolt on with our engines. Thanks fir the advice tho.
If you've figured that out, Slv49, and are still interested in playing with Ford I-6 engines...well, then, you're half way there...! :D ;)
:shock: i have a motto when working on cars-no matter how good the supplier-nothing is ever a bolt in fit!! :unsure: steve
Great stuff, Ex! But what's with the snow? I thought you lived in a tropical paradise... ;)