I have finally arrived at the conclusion that the camshaft is not stock, or if it is, it has some lobes that are not indexed right.

I'm likely to use Oregon Cams as a supplier, since they're inexpensive and close by.

For purposes of having best torque and midrange power, which cam from Oregon would you suggest?

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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'm leaning toward an Oregon Cams 819 grind. Any other suggestions? I want a smooth, strong idle, low end grunt and to pull the truck well at 1800 rpm.

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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 ran the 819 before learning that slants like more intake duration than exhaust. It worked quite well, but for your application I would do the 819 intake lobe and an 818 exhaust lobe on 107° lobe centerline. You do have stock size valves correct? I would use an installed intake centerline of 103-104° ATDC.

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Joshua

I have stainless oversize valves, and a slight oversize propane carb, on a super six intake. Right now, I have an iron manifold, until I can figure out how to ditch it to get rid of the intake heat (it sure does NOT help).

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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, with the bigger valves go 108° on the lobe separation.

In High School I milled the hot spot off the bottom of my 2bbl intake and closed off the top of the exhaust manifold with a piece of 1/4" plate steel. I just bolted it on with a stock shim gasket. There was a decent air gap between the two manifolds. Worked for sh&t on gasoline in the cool and humid NW weather, but should be good for you.

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Joshua

I put sheet metal between them, but it didn't really do a lot. The manifolds are still tied together. I suppose I could try to find someone to machine it down, but the guy who did the head just sorta snickered at the idea, saying it would cost an arm and leg. It heat soaks the intake to "too hot to touch" territory ,and in upper 90's weather, I got no power and it pings like crazy.

I'd like to have headers, but no way can I afford the new ones out there right now. I suppose even Mr Twister's power pipes would help at this point.

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

Well, I now have the closed loop controller in place and functioning and here's what I noticed: Significant power loss (must have been rich), and while accelerating, you feel a mild surging (about a 2 second cycle) , but not while steady state. The faster the engine is running the most pronounced the surge. Such as running 3400 WOT in 3rd gear, you feel a pronounced surging as it accelerates.

The solenoid cycles at about 2-3 hz (cycles per second) and it seems to update every 2 to 3 seconds. It sometimes introduces short lags while driving.

What would be the best way to determine if I have the timing at optimal?

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

The centrifugal timing is optimal when your engine has the fastest 1/4 mile time (ie, makes the most power). The vacuum advance is optimal when you get the best fuel economy. You should never be getting any pinging unless your timing is way over-advanced.

If you're still using the standard gas valve in your mixer (ie, AV1-12 or AV1-12-2), your feedback system should only really be working when the engine is cold. Normally, the standard gas valve produces a fuel mixture that is around stoichiometric. The Feedback gas valve (AV1-1245 or AV1-1245-2) is overall rich and the feedback system pulls the fuel mixture leaner to stoichiometric. Stoichiometric fuel mixtures are required for optimum emission control system operation and not necessarily for best fuel economy. When the fuel control solenoid valve is operating, it should chatter around 15-20 times per second. See bog /flat spot off idle.

If you're still using the standard gas valve, if you don't want to set the mixer's power adjustment by full-throttle CO, then you could adjust the power valve to give the best fuel economy and seat-of-the-pants power. Once set, never touch it again. Any future drivability issues will likely be due to worn or malfunctioning ignition parts.

If pinging is really an issue, you could put your EGR system back in operation. EGR is a means of reducing NOx formation by reducing peak combustion temperatures. At part throttle, the addition of an inert gas reduces the engine's volumetric efficiency, thereby also reducing its pumping losses. Since EGR relies on manifold vacuum, it has no effect at higher loads.

• EGR in spark-ignited engines
• 30 Miles per Gallon on Propane?
• My conversion: emissions results & the big trade-off
• Carburetion Best Practices

Pinging now is limited to the times when the engine gets hot. I still have no radiator fan, and it will get "hot" (210 degrees perhaps) when having to work the engine hard, but moving slow. That's when it pings now.

I have ordered cooler plugs (2 heat ranges) as once the pinging starts, it won't stop unless you cool the engine down. Not even light load or even almost no load. It will still rattle like a diesel, which leads me to think the plugs are getting hot and causing pre-ignition that's not related to timing at all.

Once I have the cooler plugs in, I'm going to experiment with the timing some more.

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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 managed to smooth out the idle more, and definitely stop the sputtering, when I found that the vacuum booster apparently leaks at least some small amount all the time, causing the #6 cylinder to misfire anytime it's not under load.

Now the surging is less, but I definitely still have a loss of power to run leaner. Not sure what to do about that, but hopefully I can find a way to get at least 10% more torque out of it, so it'll pull grades in high gear and accelerate better. It isn't gutless, it just feels "wheezy", with slow but steady acceleration up any hill. Even in third gear on a 4.5 percent grade, it takes quite a ways to get to 55, and when you shift, it immediately begins to lose speed.

Now that I'm not running rich, should I be agressive with the light load advance, pushing more advance with small decreases in manifold pressure?

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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 think you need to be conservative with ignition advance. The key thing to consider is that the pressure peak in the combustion chamber must occur so that the maximum overall torque is exerted on the crankshaft. Excessive advance just causes the pressure peak to occur too early, which wastes power and damages the engine.

Engines need more advance at part loads because the low density of air-fuel mixture in the combustion chamber. This results in a slow-burning fuel mixture which requires more advance to ensure that the pressure peak occurs at the correct time.

As for the leaking vacuum booster, lean propane fuel mixtures tend to cause lean backfires. You need to get this repaired ASAP. Interestingly, Tom Jennings came across a similar issue with the Autotronics 4046 Close-Loop Controller in his Rambler. See "Rough Idle" on that page.

I would consider using a sawzall & a belt sander on the exhaust manifold to cut down the "hot box" by 1/2" then fabricate a 1/4" block-off plate. If you don't "divorce" the int & exh manifolds, it's only a matter of time before you torch a valve or piston with detonation (you can still have damaging ping without it being audible)

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63 Valiant Wagon
225 - 4 bbl

It is very unlikely that your detonation problem is due to heat transferred to the air through your intake manifold. Even if you feel that the intake manifold is hot when the engine is idling, it will quickly cool down with higher airflow when the car is on the road.

Please have a look at the links I provided earlier. Keeping the EGR system functional has been found to both improve fuel economy and reduce NOx emissions. I do not recommend mutilating your exhaust manifold. Just fixing the manifold heat control valve in the fully hot position (closed) will be sufficient.

I think the pinging is due to needing cooler plugs and some better timing settings.

It pings MUCH easier, however, in hot weather (90+) than at 65. There's an immense amount of heat being transferred to the incoming air, so it can't hurt to cut the heat down. I'm more certain of it gaining some performance than preventing pinging.

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

If you were to measure the rise in air temperature at the cylinder head, I think it would not be very large (degrees rather than tens of degrees) even with a hot-to-touch intake manifold. The manifold heat control system is there to provide a hot spot under the carburetor to vaporize any gasoline that has fallen out of the airstream. Are you sure that you fixed the valve in the full hot (closed) rather than the full cold position? Looking from the front of the car, the valve rotates counter-clockwise to the full hot position.

To keep your air temperatures down, a cold air system would be helpful. If you have a Model 225 mixer available (148 mm / 5.83" air horn diameter), you can use a conventional air cleaner assembly, which might be easier to adapt into a ram air system. Alternatively, your Model 200's airhorn (2.625" or 3.063", depending upon model) could use a diesel truck centrifugal air cleaner.

A converter temperature control system (like Technocarb's Thermal Feedback System) could also reduce the fuel mixture temperature. I calculate that, with 90°F ambient air, 185°F LPG results in a 99°F fuel mixture while 70°F LPG results in 88°F fuel mixture. The Thermal Feedback Controller isn't currently available but you might be able to rig one up yourself. I believe your MegaJolt system has auxiliary input and user-defined output capability. You would just need a temperature sensor, vacuum switch, and a vacuum-operated water valve (fail open).