Ok, after much delays I have my propane rig on the road. It's a 70's engine in an 81 chassis. I have a 200 carb, which claims to be good for 200+ hp, so I'm assuming it should flow enough for my stock cam 225.

I did a lot of research and found that propane likes lots of advance for light load, but less than gas for WOT. I am using a Ford EDIS system with a Chrysler coil and a set of wires from a 3.3 V-6. I shaved a lot off the head, so I ended up iwth a 10.5 CR, static. It has oversize stainless valves, and all hardened seats and bronze guides.

new TC and gears, and shim head gasket.

I wanted headers, but no luck in finding used, the local pipe bender was to build me some, but never got time, so it has a regular manifold with a thin sheet of steel to help block the heat from the manifold, along with the spring being disabled on the riser valve, so it stays open.

I am using a MegaJolt Jr to control the EDIS system, which gives me a 10 X 10 matrix for programming my timing control.

Initially, I started with 10d initial, 12d at 800, 20d at 1700, 28 at 2300, 31 at 3600 and 33 at 4000. The truck would not pull a 5 percent grade at more than 35 or 40 mph.

Eventually, I've ended up with 20 at 800 36 at 1700, 41 at 2300 continuing up to 48 at 4200.

My 'light load" advance (meaning not at WOT) varies from 48 at low speed to 58 at high speed.

It simply had NO power to speak of until I began to throw vast amounts of advance at this thing. I finally reached a point where it started to ping at high speed and I backed it off just a bit.

I should not need 48 degrees advance at WOT (3600) should I?

Also, it "rumps" at idle. Nothing I can do will smooth out the idle on this thing. I'm beginning to think it has some kind of cam in it. If i were to change cams, other than stock, what would I want? I'm looking for torque, not horsepower, per se. Stock would be ok, too. This is a work truck and it runs off road quite a bit.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

Every slant six has some kind of cam in it. Are you sure your valve lash isn't too tight? How much idle vacuum do you have? Have you verified the ignition timing with a timing light? Have you verified TDC with a degree wheel? If not how are you determining your timing? How about the cam installed centerline? Was that checked?

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Joshua

Talk to Frank Raso (user name "frankraso" on here). He is very experienced with propane conversions.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I verified TDC with a dial caliper (highest spot was tdc), verified that the EDIS fires at 6 degrees before tdc default. verified that advance degrees indicated by the MegaJolt reflect real world degrees.

I just made a 450 mile trip with it, half with a tow dolly and half with a tow dolly and car, and spent quite some time reprogramming the timing curves. Of this, I am absolutely certain: Cooler outside air (like 60 degrees) makes this thing pull like a locomotive, and the warmer it is, the weaker it gets.

We found some places in the curve where the engine pinged bad and began backing things off and then tweaking the light load, as well. Here's what I have found... It likes close to 50 degrees for very light loads, and to stop pinging, I ended up at mid to upper 30's starting at 1700, climbing to 42 at 4000. At 95 degrees outside, it seems very weak, unable to pull past 55 into a 30 mph headwind, and needing 3rd gear to pull anything but the most minor grades into that headwind. On the way back, we didn't have the headwind, and it was 60 to 65 outside, and with the car on behind, we pulled the 2-3 percent grades at 55-65.

It appears I need to plumb in a cold air intake, and somehow or other I have GOT to get headers or something to remove whatever heat is getting to the intake.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

You can't just find TDC by putting the piston at the top because the piston dwells at TDC for some time. You must measure an equal distance down on either side of TDC and then TDC is in the middle.

I'm still curious about the cam/valve timing, valve lash, vacuum and A/F ratio.

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Joshua

What are your plugs gapped at? Propane needs a narrower gap,no more than 0.035. An engine makes about 15% less power on propane all other things being equal. You will gain some of it back with the higher CR.

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V8?? We don't need no stink'n V8!!

It doesn't need a narrower gap unless you're using an ignition without enough punch.

That being said, misfire is NOT a problem, the engine will NOT misfire under load, no matter how you thrash it. It starts better than any propane engine I've ever seen before. Even while moving at idle and instantly flooring it, it pulls instantly and without even a single miss.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

This is the idle sound.

http://www.youtube.com/watch?v=HNOmDqAyOfA

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

ok, here's what I know: I have set the valves (in a hurry) 3 times... first time cold, after that hot. I know they're not highly accurate, but none of them are tight - set to 12 intake and 20 exh, so I don't expect they're the issue. It ran rough before I rebuild the head, but it had 3 leaky valves and low compression on 3 cyl's.

The air fuel ratio control for idle on the carb will vary the mixture from rich to lean (identified rich by smell, lean by stalling) and the lope will not go away. I have verified no leaks, the idle is rougher if I retard the timing.

The EDIS system and megajojlt provide a VERY stable timing, it doesn't jump around even 1 degree while watching the timing with a light. FAR better than the distributor will do.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

I was hoping that someone would try a MegaJolt ignition system with a propane engine sometime. Good work!

Going back to your setup, propane generally requires more initial timing and less overall than gasoline. I think you probably have a too much advance in your map. As a starting point, you can use the 14-14-14 rule of thumb for advance. That is: 14° initial, 14° centrifugal (28° total mechanical, all in by around 2500 to 3000 RPM) and 14° vacuum. Don't go by audible knock for setting advance. Propane can be over-advanced without hearing audible knock. See LPG EGTs

Since you find that you require much more advance, I suspect you may have a fuel mixture issue. Excessively lean or rich mixtures burn slower than optimum so the additional advance might be required to compensate. If you don't notice a heavy propane smell (actually its odorant, ethyl mercaptan), my guess is that the fuel mixture is very lean.

Regarding cams (and other performance mods), generally whatever works on gasoline will work on propane. See the Stock Cams topic for more information.

Have you measured the compression in the cylinders?

What converter are you using?

What gas valve is in the mixer?

Have you verified that there is no air leakage through the EGR system and that the PCV system is working properly?

Do you have any means of measuring exhaust O2?

Ok, here is what I have done so far. Sometime, not too far back, someone rebuilt this engine. So, I thought "perhaps the cam is regrind" and I set the valves to .020 intake and .025 exhaust. SMOOTH IDLE NOW. And almost no lifter or valve train noise at all. I first tried .012 and .020, as that's where I've run well before on other slant sixes.

That made it more "peppy" on the low end, as well. It now acts like I have too much advance at the low end. So, I'll be redoing that.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

I have a closed loop fuel control system for this vehicle, but it's not yet installed. Does it run rich? No. Very lean? Don't think so.

The carb is new, it's a 200 mixer with standard valve. I have not tweaked it in any way. I didn't intend to, because I'll eventually get the closed loop system installed.

If I run 28 degrees advance @ 3000, the truck will NOT pull a 4.5 percent grade in 3rd gear beyond about 26-2800. It simply won't move. I began upping the advance while driving and ended up gaining a LOT of power by advancing things.

There is a weak propane smell at idle and I don't know about under load.

I noticed that there is a valve in the vapor intake that says something about "load", but I have not touched it. Should I?

Thanks

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

There are four fuel mixture adjustments on a propane system:

• idle mixture
• power mixture (often labeled "load")
• gas valve profile
• gas supply pressure

The idle mixture screw controls fuel mixture at idle.

The power mixture valve is adjusts the restriction in the fuel supply to the mixer. Its effect is most prevalent at full load and has minimal effect on fuel mixture at low loads.

The gas valve is a variable fuel supply orifice that opens in direct proportion to air flow and is controlled by internal mixer vacuum. There are several gas valves available with different profiles.

An Impco converter can deliver either -1.5" WC (Water Column) or -0.5" WC pressure to the mixer, depending upon which secondary regulator spring is installed. Normally, the blue spring (-1.5" WC) is used in automotive systems.

The factory sets the position of the power mixture valve and there is generally no need to adjust it. It is possible that this valve has been moved prior to installation. You can adjust this valve on a chassis dynamometer at full load to around 2.0% exhaust CO for maximum power. See Impco Fuel Mixtures.

To test your theory, I snapped a picture of the position of the load valve, and turned it toward "R". It was in the very center.

Immediately, the truck gained power and started pinging like mad. I re-wrote my advance curve to reduce max advance to around 28, and max light load to about 44 (3000 rpm, no load). It made a stunning difference, in that the truck has more power by far than it had on gas, and requires far less advance to pull well.

So, yes, it was apparently running extremely lean. I'll fiddle more with it later, tweaking the load valve back towards lean until the engine begins to lose power significantly.

Next week, I'll try to get the O2 sensor bung put in and see if I can't get the Commander closed loop system installed and working.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

Be careful about running a rich fuel mixture as gaseous fuels do not have an evaporative cooling effect on valve temperatures like gasoline. Since rich mixtures tend to burn hotter and slower, the fuel mixture could still be burning when the exhaust valve opens, which could result in torched valves. It is safer to keep the fuel mixture on the lean side and this is best done by measuring full load exhaust CO.

As for feedback control on fuel mixture, the system is designed to use the feedback gas valve (PN AV1-1245-2), which is overall richer than the standard gas valve (PN AV1-12-2). The Commander system adjusts the pressure delivered by the converter to lean it out based on feedback from the O2 sensor. Therefore, the Commander system can only lean the fuel mixture to stoichiometric.

You can use the Commander system with the standard gas valve but it will only keep the fuel mixture from becoming richer than stoichiometric. The converter is a pressure regulating device and the supplied fuel density will be greater when the engine is cold. If you make a lot of short trips with your truck, the Commander system will improve your fuel economy with the standard gas valve. If your truck runs for several hours at a time, the fuel economy improvement will be much smaller.