gas to lp conversion

1968 403 · Oct 30, 2013

I am thinking about converting a c263 gas engine to LP. We have a Super M already on LP I am set up to fuel LP tractors here at home. The 263 engine has firecrater pistons. MY question is how much power and fuel economy will I loose converting the 263 to LP if I do not raise the compression of the engine. LP is half the price of gas here. I plan on using Impco parts. All replys appreciated

Anonymous-0 · Oct 30, 2013

Based on BTU's of gasoline vs. propane...about 10%, unless you increase the compression, if I recall correctly.

Chuckles46 · Oct 30, 2013

I would pull the head and have it gone thru before the conversion Plane the head to make it true. If it has valve rotators deactivate them. In a 560 that engine should make 65hp plus pto. Make sure to recurve the distributor for best performance.

1968 403 · Oct 30, 2013

How much can I take off the head without the firecraters hitting the head?

Heat Houser · Oct 30, 2013

This is memory so...
The lp head had stellite exhaust valves and seats. Reduce the time between valve lash adjustments if using a std head.

The distributor advance curve was a bit different as well, along with the timing setting.

High compression pistons

Exhaust and intake manifolds totally separated.

All that I can think of right now.....

redvalley · Oct 31, 2013

do you have the tank and sheetmetal? I have if needed. I have one I bought to supply some other parts for my dads 560LP we have had since the . 70"s. love it. call 319-330-5848 to discuss.

Russ600 · Oct 31, 2013

Hi.

I did a lot of lp conversions over the years in pick ups. Mainly big block Chev. and Ford, and I always had good service with Impco kits. IH had those engines with factory lp so I would use their spec for the timing. If your engine has valve rotors I would take then out as propane is a dry fuel. As far as changing valves at the time of the converation, I would hold off until it starts to give trouble. I have run some big blocks chevs over 100,000 miles before I did the heads. If the head has been overhauled since unleaded gas was the norm it may already have better valves and seats which last pretty good. Also use the IH spec for the spark plugs, generally propane engines require a hotter plug. I go along with the 10% loss in power but it makes up for it with the savings in fuels costs.
Cheers
Russ

1968 403 · Oct 31, 2013

How much trouble is it to tae the valve rotators out?

Owen Aaland · Nov 1, 2013

On the trucks I worked on they just put a spot of brazing on the rotators to keep them from turning when they did the conversions. When the heads were removed for service the rotators would be replaced with standard retainers. Starting about 1990 they no longer even did that much. It did not seem to make much difference in valve life.

If you have a later C263 you will already have Stelite valves and hardened seats in the head.

1968 403 · Nov 1, 2013

Thanks Owen The engine is a 1968 year model. I have been told it already has hardened seats and exhaust valves. Thanks everyone foe all the good advice. Keith

gas to lp conversion

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