Where to get an LPG Conversion Kit or D.I.Y. info?

**White Whale** · 11-07-04 03:24 PM

Hello all,
I have been trying to get some info from the Net on converting a Big Block Caddy to LPG, and can't get straight info, just a lot of "give us your personal info and we will get back to you".

I need a site that will discuss theory, parts and install for the D.I.Y guy.
Thanks,
Mike

**davesdeville** · 11-08-04 02:23 AM

Carbureted LPG is fairly common. I'll post a couple links:

http://www.propanecarbs.com/propane.html
http://wps.com/LPG/
http://wps.com/LPG/LPG-book-final.html
http://franzh.home.texas.net/engine.html
http://www.impco.ws/

Liquid propane injection is it's own animal, no one has parts for it really, and I haven't got a clue about gaseous injection.

**White Whale** · 11-08-04 10:00 AM

Thanks for the links.
The second link looks like a great site, though I can't get the online manual to work.
Mike

**pdoke2003** · 11-17-06 01:44 AM

anyone end up doing this on a 500 or 472? I'm very interested in it as I'm putting a 500 in my jeep when I finish it. I cant afford EFI or special offroad carbs and regular carbs just don't cut it on the angles. from what I've read LPG eliminates the problems with angles.

**BluEyes** · 11-19-06 12:00 AM

pdoke - for offroading you should consider that if you run out of "gas" out somewhere in a propane engine, getting a refill might be a little difficult. Dual fuel conversions existed back in the '70's, so you might want to keep the capability of running on gasoline. You might also look at Megasquirt EFI for low cost DIY injection. Or read Dour Roe's book: Rochester Carburetors. I believe he has a few modifications for Q-jets for high angle useage.

If propane were more widely available, I think I'd do a full conversion on my Caddy. Take a '74-'76 shortblock with the flattop pistons and match that with 76cc heads for the reported 12:1 compression which works great with propane (and will help reconver some of the lost power and mileage) but would keep me from running gasoline at all...

**davesdeville** · 11-19-06 05:23 AM

If you manage to run out you have a problem, but the availability of propane is pretty good. I think I'd convert a grille tank into a kind of gas can, and carry it as a reserve. With all the RV people that use propane, it can be found along every major road if you know where to look.

**pdoke2003** · 11-19-06 09:28 PM

there is a few places to fill near between where I offroad and my home so that's not really a concern and acording to some of the sites I read 2-10gal tanks(what I plan on running) should give me about 16 hours of hard wheelin', plenty of time to get back to one of thoes place. as for the BBQ tank as a gas can, I've actually read that on a few sites and it seems like a good idea to atleast get to the next filling station if I happen to run out.

**pdoke2003** · 11-21-06 03:19 PM

Originally Posted by BluEyes

pdoke - for offroading you should consider that if you run out of "gas" out somewhere in a propane engine, getting a refill might be a little difficult. Dual fuel conversions existed back in the '70's, so you might want to keep the capability of running on gasoline. You might also look at Megasquirt EFI for low cost DIY injection. Or read Dour Roe's book: Rochester Carburetors. I believe he has a few modifications for Q-jets for high angle useage.

If propane were more widely available, I think I'd do a full conversion on my Caddy. Take a '74-'76 shortblock with the flattop pistons and match that with 76cc heads for the reported 12:1 compression which works great with propane (and will help reconver some of the lost power and mileage) but would keep me from running gasoline at all...

you would trust the stock bottom end at 12:1 compression? most people here don't seem to think thats such a good idea, but thats probably what i'll end up doing if I can't afford forged rods and pistons. Also CaddyCarlo says he's running stock pistons and rods with 12 lbs of boost and nitrous and has had no problems, and I've always believed in trusting first hand expirience over hearsay. So assuming he's not lying I think I'll be fine.

**davesdeville** · 11-21-06 06:49 PM

It'll live for quite awhile on 12:1 from what I've read.. The stock bottom end will survive a LOT of abuse.

**pdoke2003** · 11-21-06 11:49 PM

I won't be running it above 5,000rpm eaither, and from what I've read on here high rpms seem to be the biggest killer of these things.

**davesdeville** · 11-22-06 02:59 AM

That's very true, the stock valvetrain is a POS over 5250 or so.

**BluEyes** · 11-29-06 07:01 AM

Originally Posted by pdoke2003

you would trust the stock bottom end at 12:1 compression?

With propane it won't know the difference. The bit of extra force that it takes to compress the charge 12:1 instead of 10:1 is still nothing compared to the force on the piston when the charge is ignited.

The problem with high compression is usually the possibility of preignition, aka spark knock, detonation, etc. The sudden pressure spike that this causes goes way past anything that any motor can take for an extended period, forged pistons or not. But, the octane rating of propane is way up there and 12:1 is no problem, think race gas. Propane would be happier with something around 14:1, IIRC. So a 12:1 Caddy on propane could probably be considered a low compression motor, lol.

**pdoke2003** · 11-29-06 11:10 AM

ok that's what i figured. I've read that average compression for LPG is between 12:1 and 15:1 so you are right it will be considered a low compression engine. I might get the block and heads shaved a little to up it some but I'm not I'll have the money or if the small amount I could shave without having to get the intake done as well will even be worth it.