I had a sort of crazy Idea last night . . .

[jjester6000]

Last night I fired up the barbecue and got thinking about whether or not I could convert my 1974 GMC C1500 to Propane. Make it an Oil-Gas-Propane hybrid.

Since Propane is cheap and not much less efficient than gas, so I know that I would save money on gas.
(I ran the numbers a while back)

I was thinking that I could start it up on gas and run it on propane. My issue is that I don't really want to install an electric fuel pump, I like the mechanical one, so what if I created a bypass valve that redirected the flow from the pump back into the tank? So I can switch it back to the carburetor at any time from a switch on my dash.

I made a couple diagrams until I ran into a problem, I need to reference the flow of propane with the position of the throttle. Since propane is delivered as a gas, not a liquid, it won't fill the float bowl/get pushed by the accelerator pump, so I have to modify my carburetor.

What do you think? I have most of the junk laying around to do this, I just need a way to reference the flow of propane with the throttle position. (I got some Ideas, but I would need some sort of low resistance gas valve in order the throttle to return, not an off the shelf one).

 

[1987 GMC Jimmy]

@shiftpro

 

[Dutch Rutter]

Last night I fired up the barbecue and got thinking about whether or not I could convert my 1974 GMC C1500 to Propane. Make it an Oil-Gas-Propane hybrid.

Since Propane is cheap and not much less efficient than gas, so I know that I would save money on gas.
(I ran the numbers a while back)

I was thinking that I could start it up on gas and run it on propane. My issue is that I don't really want to install an electric fuel pump, I like the mechanical one, so what if I created a bypass valve that redirected the flow from the pump back into the tank? So I can switch it back to the carburetor at any time from a switch on my dash.

I made a couple diagrams until I ran into a problem, I need to reference the flow of propane with the position of the throttle. Since propane is delivered as a gas, not a liquid, it won't fill the float bowl/get pushed by the accelerator pump, so I have to modify my carburetor.

What do you think? I have most of the junk laying around to do this, I just need a way to reference the flow of propane with the throttle position. (I got some Ideas, but I would need some sort of low resistance gas valve in order the throttle to return, not an off the shelf one).

a googling led me to this. https://www.fourwheeler.com/how-to/engine/131-0803-dual-fuel-propane-system-install/
Sounds like they did something similar. Hope it helps.

 

[shiftpro]

Hi Jack,
it seems you might have some incorrect information.
Why would you need to start on gas and switch to 'pane?

Propane engines are NOT HARD TO start even in cold climate.

Dual fuel never worked right because your timing is compromised. With 'pane you want a little more initial, less overall but much faster ramp up of advance. So all you need are light springs in you HEI.

Propane has less BTUs than gas but the octane is way up there. That means you can build 10.1 or 11.1 compression ratio engines.
This will make up for the power loss.

Propane 'carbs' are called mixers and basically there is only one available. And they are cheap almost free in wrecking yards.
It's called and Impco 425. They only flow about 450 but can be richened up with two regulators (evaporators) feeding it.
Anything bigger than a 350 should have two evaporators at the least, but best is a dual carb setup with two 425s and two regulators.

I'm running a 454 with one Impco and it's vastly undercarburated, but still works. Power just runs out at 3000rpm.

Propane is super easy to tune. No jetting worries. If it's lean it will not produce good power. Lean running will NOT burn pistons.
If it's too rich, under full throttle extended service then it will overheat. But too rich is very very obvious... stinks like 'pane over the top.

With 'pane you can run single plane of even tunnel ram intakes, and it loves it. Yes you can run tunnel ram intakes on the street with no problems whatsoever.

You can add nitrous to propane also, but don't have any experience with this.

Old school systems, like I'm describing only need a tank, vacuum controlled safety valve, evaporator (regulator), and mixer (Impco 425 carb). These are called open loop systems.

You can get closed loop kits for fuel injected cars. There would be an additional computer to piggy back the existing ECM. They work awesome but cost about three times more than new open loop systems.

This last spring I opened my 454 after some 185,000 kilometers, almost all on 'pane. Truck (my avatar) is an 81 and was converted around 83. It was absolutely spotless inside the engine. Still hone marks on the cylinders. No ring groove. Yes a valve burnt out but look at how many Ks were on it.
You don't have to occasionally run gas to 'lubricate' the valve... more ********.
Propane basically got a bad rap from the dual fuel systems. If you have dual fuel and run 'pane too often your carb will go for a ****.
The when you switch to gas it leaks.

 

[DoubleDingo]

A friend of mine had dual-fuel on his truck. It would run fine on gasoline until it wouldn't, then he had to switch it to propane. It would run fine on propane until it wouldn't, then he had to switch it to gasoline. I've known others with a dual-fuel setup that never had that problem, but for some reason the truck he had preferred to run gasoline, and then propane, and then gasoline, etc. It was crazy.

 

[shiftpro]

Propane engines can idle down to 500rpm easily. Don't run retro-roller lifters with needle bearings if you want that low sweet idle...
not enough oil at 500-600 rpm. LUNATI told me this a few years ago.

 

[shiftpro]

Pane like wide LSA cams. Think blower cam or marine.. The liquid pane expands like a fat chick in a dougnut shop. As soon as it hit air it turns to a gas and away it goes. It's expanding all the way down through the intake and into combustion. Then the hot gases after boom time continue to expand all the way out the tail pipe. Pane loves good flowing heads and big valves, headers and big tail pipes.
If you heads flow, especially on the exhaust side, then a symetrical cam is welcomed.
And compression compression compression.
And every engine likes a narrow quench like .350 AFTER the head gasket is compressed. Actually .040 is fine if you want to feel more safe... or don't trust the gasket manufacture's crushed thickness specs.

Sorry I can't spell very ggot today... too sober..?

 

[shiftpro]

https://fuelsforum.rasoenterprises.com/viewforum.php?f=5&sid=7fb10edc6f7115c2e8c6c9bdb4c82557

 

[78C10BigTen]

Lotsa crazy info here i never knew.... only pane vehicle ive used is the 4cyl komatsu forklift at work.

 

[jjester6000]

Hi Jack,
it seems you might have some incorrect information.
Why would you need to start on gas and switch to 'pane?

Propane engines are NOT HARD TO start even in cold climate.

Dual fuel never worked right because your timing is compromised. With 'pane you want a little more initial, less overall but much faster ramp up of advance. So all you need are light springs in you HEI.

Propane has less BTUs than gas but the octane is way up there. That means you can build 10.1 or 11.1 compression ratio engines.
This will make up for the power loss.

Propane 'carbs' are called mixers and basically there is only one available. And they are cheap almost free in wrecking yards.
It's called and Impco 425. They only flow about 450 but can be richened up with two regulators (evaporators) feeding it.
Anything bigger than a 350 should have two evaporators at the least, but best is a dual carb setup with two 425s and two regulators.

I'm running a 454 with one Impco and it's vastly undercarburated, but still works. Power just runs out at 3000rpm.

Propane is super easy to tune. No jetting worries. If it's lean it will not produce good power. Lean running will NOT burn pistons.
If it's too rich, under full throttle extended service then it will overheat. But too rich is very very obvious... stinks like 'pane over the top.

With 'pane you can run single plane of even tunnel ram intakes, and it loves it. Yes you can run tunnel ram intakes on the street with no problems whatsoever.

You can add nitrous to propane also, but don't have any experience with this.

Old school systems, like I'm describing only need a tank, vacuum controlled safety valve, evaporator (regulator), and mixer (Impco 425 carb). These are called open loop systems.

You can get closed loop kits for fuel injected cars. There would be an additional computer to piggy back the existing ECM. They work awesome but cost about three times more than new open loop systems.

This last spring I opened my 454 after some 185,000 kilometers, almost all on 'pane. Truck (my avatar) is an 81 and was converted around 83. It was absolutely spotless inside the engine. Still hone marks on the cylinders. No ring groove. Yes a valve burnt out but look at how many Ks were on it.
You don't have to occasionally run gas to 'lubricate' the valve... more ********.
Propane basically got a bad rap from the dual fuel systems. If you have dual fuel and run 'pane too often your carb will go for a ****.
The when you switch to gas it leaks.

That has given me something to think about, The engine I am running is a tiny little 250 i6, and I am still running points.

I got the head from a 194, that I am in the process of rebuilding and planning to use to boost compression up to 10:1.

I really want to use what I already have and just modify it.

 

[Snoots]

Discuss it, argue about it, whatever. I'll just burn dead dinosaurs and have fun rather than have it sit up waiting for me to 'fix' it.

 

[shiftpro]

Go back and hit the 'like' button you tight wads...

 

[shiftpro]

That has given me something to think about, The engine I am running is a tiny little 250 i6, and I am still running points.

I got the head from a 194, that I am in the process of rebuilding and planning to use to boost compression up to 10:1.

I really want to use what I already have and just modify it.

Well don;t go spending money on high compression pistons for your 6. Buy domed and forged pistons for your 496...

 

[jjester6000]

Buy domed and forged pistons for your 496...

If only. . .

 

[eskimomann209]

I too got learnt today... solid info @shiftpro