Ignition timing with LPG

[8literbeater]

What are the opinions on this timing curve?
It's a Chevy 250, with 10# of boost (right now, I might go lower), and of course it's running propane. It's draw through, with no intercooler. I called NGK back when I bought spark plugs, and bought the plugs that the tech recommended, based on these things. (Hotter for propane, cooler for turbo, I can't remember which way for the altitude here, and another step cooler because of the normally high ambient temperatures here.) Update: I checked the plugs, and they're UR6. The original spec plug is UR4, so these are 2 steps cooler.

I don't really care how much power it makes, as long as it runs smooth, and I'd like to get decent mileage. I'm not using the vacuum advance right now, but I ordered one that only advances 5°, and starts coming in at 6"Hg, and the full 5° at 13"Hg. As long as it does what it's supposed to do, I'll put that on later.

The blue is what I got from testing my current setup. The red is what I'm thinking of setting it to.
The problem is, since my tach doesn't work, I can't say where the boost is coming on, or how fast.




I found some interesting stuff in this book. ↓↓↓

ASTM LP-Gas Engine Fuels STP-525
https://books.google.com/books?id=Cm...%20130&f=false

 

[8literbeater]

For what it's worth.

 

[8literbeater]

That's on 8 pounds, and I did change the timing a little, but I don't remember it right now.

For mixture, here are the first few runs where I dialed in the mixture. Something I thought was interesting, is that when it was lean, it got leaner and leaner as RPM went up. When it was on point, or even rich, it stayed pretty level as RPM went up, but actually got a little richer on the high end.

That little drop in power between 1600 and 1800 is when it hits 2 pounds, and the timing *******. You can see how much sooner it builds boost when the mixture is right.

 

[PA41]

That looks like it'd be great to drive. Big torque is fun, like you are always coasting down a hill. So this LPG is easy to adjust fuel flow for richening up?

 

[8literbeater]

That looks like it'd be great to drive. Big torque is fun, like you are always coasting down a hill. So this LPG is easy to adjust fuel flow for richening up?

It's really easy in theory. Theres a knob on the mixer where the vapor line goes in. It's marked L and R, for lean and rich. The problem is that there's no baseline to go by. There's no jet sizes, or number of turns, or any way to set it based on altitude or any predictions. You don't even get the black smoke for rich, or high exhaust temperature when lean. I don't think there's any way to set it correctly without an A/F ratio meter.

The other thing is that you have to make very small adjustments. A little movement gives a big change. The first picture is where I started, and it was running up to 16:1 and climbing. The second picture is where I left it, where it's about 13:1. The other one marked "idle", is a cover. You unscrew that, and there's a normal idle mixture screw under there. It's really sensitive too.

 

[PA41]

How about the detonation situation with added boost, or too much advance? Does propane predetonate like pump gas? I see you are retarding the timing but don't have an intercooler. I know that propane need heated to turn into gas quicker, does that have something to do with the no intercooler? I've owned a propane vehicle many years ago, and other than the lower performance, I liked it. (I didn't pay road taxes back then) It was a v6 GMC with 300,000 miles on it. When it locked up I tore it down and although it showed a little wear it was really fresh, but the crank had broken. I guess just metal fatigue.

 

[8literbeater]

How about the detonation situation with added boost, or too much advance? Does propane predetonate like pump gas? I see you are retarding the timing but don't have an intercooler. I know that propane need heated to turn into gas quicker, does that have something to do with the no intercooler? I've owned a propane vehicle many years ago, and other than the lower performance, I liked it. (I didn't pay road taxes back then) It was a v6 GMC with 300,000 miles on it. When it locked up I tore it down and although it showed a little wear it was really fresh, but the crank had broken. I guess just metal fatigue.

It can detonate, but it's equivalent to about 110 octane. So you can run it with a lot higher compression or boost. When I was running 10 pounds, I did get a couple of knocks at full throttle. That's when I turned it down to 8.

There are a few reasons for not having an intercooler. First, it's just easier and cheaper to not put one on. Having high power output isn't all that important to me. I like to mess with it and see how good I can get it to run, but it isn't a race car. Next, being a draw-through turbo system, it's not recommended to run the fuel through an intercooler. If I wanted to run an intercooler, I'd have to make it a blow-through, and this propane setup is vacuum operated. I would have to use a new liquid propane injection system with a computer. I wanted a turbo, but still tried to keep it simple.

Propane turns to gas at -44°F. Likewise, it freezes up the regulator if the regulator isn't heated. If you lived in cold country, I don't know if or how you would start a propane-only vehicle in the cold, because like you said, it would need some heat to get it to turn to gas. I suppose you'd need a block heater to keep the water warm, since the water runs through the regulator to heat it. For vehicles in cold country that are dual fuel, they always recommend starting on gasoline, then switching to propane after it's warmed up.
Anyway, in a propane system like this one, the regulator is heated sufficiently to vaporize the liquid when it goes from about 320 PSI, down to 1 or 2 PSI (not sure about the vapor pressure). Actually, they call the item a vaporizer, not a regulator.

To sum it up:
LPG is actually a mix of 90% propane, and some other stuff, and it's about 110 octane, so it acts kinda like race gas.
I can't run an intercooler, but I don't really need one, and don't care about the lower power.


Propane powered engines will go forever. They just don't get any wear, except for metal fatigue like you said. I met a guy a while back that had a 2002 (thereabouts) Chevy pickup with 550,000 miles on the original engine, running on propane. He had replaced 3 transmissions, and 2 rear ends.

 

[Dirtyrat]

Sounds like an interesting thing to tune =)
I'm going to be right there with you once I get a supercharger fitted...
And I also concur on the going forever, there is little to no contamination in the oil ever with propane powered vehicles...

 

[8literbeater]

Sounds like an interesting thing to tune =)
I'm going to be right there with you once I get a supercharger fitted...
And I also concur on the going forever, there is little to no contamination in the oil ever with propane powered vehicles...

You run something like the Roush liquid injection system don't you? So you could run an intercooler if you want.

 

[Dirtyrat]

You run something like the Roush liquid injection system don't you? So you could run an intercooler if you want.

yea, I am running the roush setup, I plan on running the stock ford setup which is water to air..