Propane engine builds (tech, questions, advice)

Elliott · Nov 21, 2012

For six g's go by an ls3 and be miles ahead on power and reliability.

altfuel1991 · Nov 21, 2012

AllGoNoShow said:
Buddy, I went wheeling this weekend and the engine would "load up" on tough sections. It would not build any RPM and would just spit and sputter while trying to climb. The tanks are in the right position, the tanks were full. When there was not a load on it, there was a slight stumble right off idle, then it would clear out. It suddenly started doing this for no apparent reason. Your thoughts?

What is the base timing and centrifugal curve set on? Have the power mixture settings been altered? Usually when there is a stumble just off idle it is caused by an ignition problem. What kind of plugs(standard tip, platinum) and what are the gaps set at? It also is possible one of the vaporizers could be over pressurizing. You can check the pressure at the test port on the side. It should have about 1-1/2 lbs pressure when running. Anything over 2 lbs and it will try to flood the engine. Has anyone checked the lever height in the top of the vaporizers? If the problem started all at once you could have a defective vaporizer.

TBItoy · Nov 21, 2012

halcat said:
You no, all this propane swap started out years ago because it was an easy way to get a carborated engine to run in off camber angles off road. With this article now you have to build a special motor for pane. I think building a motor for propane would be fine if you were going to drive say 200 k miles and take advantage of it's cheaper price . All thow I did,most people don't build motors just for off road, we use what we got, dig one out of the junk yard put on our fuel system and go . Looks to me like you would Be better off spending your money on a good after market stand alone injection system and ride! That's what i did. When i take a notion to go wheeling on sunday morning I dont have to wonder if I got full tanks I stop by co-op, swipe my card, fill up and I'm off!

I'm inclined to agree. I don't think I'll spend any $ on "building" a propane engine out of my current 351W.

Especially since I could buy a low miles 5.3 or 6.0 that already has aluminum heads for less $. I can cut down a harness myself andI have EFILive for tuning my Dmax, so I could put a wideband on the GM engine and tune on it myself.

altfuel1991 · Nov 21, 2012

halcat said:
You no, all this propane swap started out years ago because it was an easy way to get a carborated engine to run in off camber angles off road. With this article now you have to build a special motor for pane. I think building a motor for propane would be fine if you were going to drive say 200 k miles and take advantage of it's cheaper price . All thow I did,most people don't build motors just for off road, we use what we got, dig one out of the junk yard put on our fuel system and go . Looks to me like you would Be better off spending your money on a good after market stand alone injection system and ride! That's what i did. When i take a notion to go wheeling on sunday morning I dont have to wonder if I got full tanks I stop by co-op, swipe my card, fill up and I'm off!

There is no need to build a special motor for normal weekend running. Propane is still the cheap and simple way to have fun. Most standard engines will last a long time without any issues. My Silverado with 4.3 engine has been on propane for 6 years and is driven daily without any internal changes. It has about 160K miles on it right now.

halcat · Nov 21, 2012

You are right about weekend wheeling and special motors but this thread started out on how much power you can get if you build for propane and what are the limits of one mixer. I have ran propane with single and duel mixers, and it is simple to set up on a stock engine with let's say 250 to 300 hp. I know YOU can get 600 hpwith propane but not all of us can. My latest engine is a 489 stroker that makes 600 hp 625 tq with fast 750 cfm fuel infection and it tunes itself. I know some body can take this engine, put it one pane get that kind of power out of it, but I can't. If you build for gas like I did with 10 to 1 motor it can be switched to pane someday, but if you build for pane with 12 to 1 it can't go to pump gas. And let me question anybody that says they can take and build a propane engine that will blow the tires off a rig like mine will off idle .gas is bad ass!

Bubba1 · Nov 21, 2012

Propane vs Gas drag races sounds fun

AllGoNoShow · Nov 22, 2012

altfuel1991 said:
What is the base timing and centrifugal curve set on? Have the power mixture settings been altered? Usually when there is a stumble just off idle it is caused by an ignition problem. What kind of plugs(standard tip, platinum) and what are the gaps set at? It also is possible one of the vaporizers could be over pressurizing. You can check the pressure at the test port on the side. It should have about 1-1/2 lbs pressure when running. Anything over 2 lbs and it will try to flood the engine. Has anyone checked the lever height in the top of the vaporizers? If the problem started all at once you could have a defective vaporizer.

I am not sure what the timing is, I never have put a light on it. I just timed/tuned it by feel and sound. I have messed with the power settings. Prior to the last run I turned the middle adjuster (wide open mixture) counter clockwise to richen it. It then ran like crap when I went crawling. Therefore, I leaned it back out and played with the idle mixture a little. Richening the idle seemed to help it a little. I have platinum spark plugs, is that what it should have? Not sure on the gaps, it was the same as when I had the carb on it. Like I said, prior to this run, it ran fine. Between this run and the previous, I did mess with the wide open mixture. Maybe that is it?

altfuel1991 · Nov 22, 2012

AllGoNoShow said:
I am not sure what the timing is, I never have put a light on it. I just timed/tuned it by feel and sound. I have messed with the power settings. Prior to the last run I turned the middle adjuster (wide open mixture) counter clockwise to richen it. It then ran like crap when I went crawling. Therefore, I leaned it back out and played with the idle mixture a little. Richening the idle seemed to help it a little. I have platinum spark plugs, is that what it should have? Not sure on the gaps, it was the same as when I had the carb on it. Like I said, prior to this run, it ran fine. Between this run and the previous, I did mess with the wide open mixture. Maybe that is it?

The timing is critical on any engine in order to make proper power, torque and idle. Propane has a different curve and takes less total timing than gasoline. Also the 425 mixers are preset for the proper power air/fuel ratio when manufactured so there could be a problem there. the idle mixture is the only adjustment that should be made after the timing is set correctly. Also platinum plugs are not good for alternate fueled engines, with the exception of liquid injection, because with the hotter combustion temperatures platinum absorbs heat and turns into a glow plug under load. A standard tip spark plug is sufficient and last as long as any other plug. It sounds like you need to start with getting the timing AND spark curve optimized first and replace those platinum tip plugs and see how it runs before going to the next step.

throttlejunkie · Nov 22, 2012

Bubba1 said:
Propane vs Gas drag races sounds fun

Thank somebody just got called out! :dunno:

Bubba1 · Nov 22, 2012

throttlejunkie said:
Thank somebody just got called out!

With a smaller motor on propane. Haha

altfuel1991 · Nov 23, 2012

Bubba1 said:
Propane vs Gas drag races sounds fun

We have done it with other forms of transportation. The mini bike is a prototype the manufacturer tested against a gasoline version.
On a 300' track the propane version was faster in the first 150', after that the gas version picked up. At the end of the track the propane
version was .2 seconds slower.

AllGoNoShow · Dec 19, 2012

Altfuel

I installed a new HEI distributor in my truck, and without timing it I can already tell that it has helped the problem alot. What should I set the initial and total timing at? It is a 460 Ford with a straight up timing chain. I have read that I should set it at 14btc initial, and 34-38 total. Does that sound right for propane?

Fire Freak · Dec 19, 2012

Bronco Buster said:
If you want to know how to build a big HP motor with a 425 mixer. Find a guy that builds winning round track motors for hobby classes. I know when I was into dirt track we were getting 500 plus HP with a 500 cfm motorcraft 2150 carburetor. Nascar makes 700 plus with 600 cfm on restrictor plate tracks so anything is possible.
There is a someone on here (Little Tim) that has a big block chevy that I have heard is over 500 cubes and I'm sure has well over 650 HP on dual mixers.
All of this is a major reason I have been talked out of propane. If it will only support a stock motor (325 hp) I don't want it. I can do a decent efi for about the same price as a dual mixer and have less headaches and better mileage. I know a guy with dual mixers that will go through 7 gals of propane sitting in the shop faster than I go though 7 gallons of gas on the trail. :****:

yeah i got that fixed i hope

Fire Freak · Dec 19, 2012

This is the setup witha an intake like the black one

peanut · Dec 20, 2012

if he is runig through a bottle just ideling he has major problems

Fire Freak · Dec 20, 2012

Yeah had my idle screws way to far out fixed it

Bronco Buster · Dec 20, 2012

peanut said:
if he is runig through a bottle just ideling he has major problems

LOL I was kinda pokin fun it was Fire Freaks setup. Tat was not just idling it also included him breaking in his cam and doing some other tuning. I was just giving him hell because he used almost a whole bottle and hadn't even got it out of the shop yet.

ridered3 · Dec 30, 2012

So I've been looking at a few propane powered rigs here lately. If it was going to be trail rig only, I don't mind the thought of propane, but I'm wanting more of a dual purpose rig (drive there, wheel, drive home). How hard would it be to swap the propane setup off the rig, or would propane power be alright in a dual purpose rig?

xjpaddler · Dec 30, 2012

ridered3 said:
So I've been looking at a few propane powered rigs here lately. If it was going to be trail rig only, I don't mind the thought of propane, but I'm wanting more of a dual purpose rig (drive there, wheel, drive home). How hard would it be to swap the propane setup off the rig, or would propane power be alright in a dual purpose rig?

only down side would be carrying extra tanks with you to and from the trail

ridered3 · Dec 30, 2012

xjpaddler said:
only down side would be carrying extra tanks with you to and from the trail

I believe both vehicles have dual tank mounts in the bed. The local TSC fills tanks and I figure the 22r's would just sip the propane all weekend, but was curious about some of the other pros and cons for it.