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65CrewCabPW
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PostPosted: Wed Sep 07, 2011 10:59 am 
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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).
Heat valve is free turning, but the spring that closes it has been "liberated" so that there's no tension to close it.

I'm working on an idea to get cool air from in front of the radiator for the intake, and also a modified manifold with no heat box at all - found one for sale.

I don't know how to build a hysteresis type system to keep the converter at a steady temperature. Otherwise, it's obviously going to swing wildly, and the "cold" swings upon sudden demand with the water not flowing could be a problem.

I am going to try a flow limiter...

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.
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FrankRaso
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PostPosted: Wed Sep 07, 2011 11:47 am 
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Joined: Fri Apr 16, 2004 10:50 am
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Location: Stevensville, ON
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I believe the heat control valve is designed to close with high exhaust flow. However, I don't think it would hurt to force it closed as I think it might be able to hang partly open at low exhaust flow.

As for a water control valve for the converter, it think it would work a bit like the fuel system's fuel control valve: constantly opening and closing around the setpoint. Even though water flow would fluctuate, gas temperature would relatively steady. During acceleration, the loss of manifold vacuum would cause the valve to fully open and provide full water to prevent the converter from freezing. If you bought the MegaJolt system from AutoSport Labs, they could probably help you.

A flow limiter (like the Gann M-456) doesn't work really well. See increasing density by reducing coolant temperature.
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65CrewCabPW
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PostPosted: Fri Sep 09, 2011 5:42 pm 
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Today was hotter than normal. I changed plugs to 2 heat ranges cooler - NGK UR6 - pulled the timing back 5 degrees, and yet, a half mile of 4.5% grade had the engine pinging radically and so little power it would barely pull the hill at all. Upper 90's today.

What I eventually noticed, was that as the closed loop system worked, it pinged and stopped as the mixture wandred back and forth. It would stop pinging, but the power just died when it did.

The plugs, which have 1500 miles on them, are tan on the insulator and electrode.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.
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65CrewCabPW
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PostPosted: Sun Sep 11, 2011 6:45 pm 
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Today was cooler, and I set out to see what I could do. With the cooler plugs installed, and the timing set back, I found that just shifting into 3rd and flooring it at 1200 rpm will result in serious ping rattle by the time the engine makes 3400 rpm. Not one cylinder, but all. I pulled the timing back so far the truck can barely pull itself to 60 mph on a .5% grade, and it still pings just as bad. Timing seems to have no effect on the pinging noise.

Basically, you just pull hard above 2500 and it takes from 10 to 30 seconds before it the pinging is so bad it sounds like the engine is coming apart. And, when you let up, you have to let up to the point where you're all but not even using engine power to get it to stop. I let up, shifted to third and let the engine run fast, but no demand. Then 2nd, and I slowed down to 10 mph on a gravel road and trying to move the truck at that speed resulted in wildly radical pinging.

Hit the clutch and try to rev the motor in neutral and it hammers. Again, not one cylinder, but apparently... ALL of them.

Get on a grade, and lug the engine at 1500 at WOT and indicated 24 degrees timing and it'll slowly begin the death rattle noise after a while. I pulled the timing back 5 more degrees... No power at all, but still ends up knocking.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.
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65CrewCabPW
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PostPosted: Sun Sep 11, 2011 6:47 pm 
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Post note: If I do this at night, when it's 60 degrees? Has much better power and .... Normally won't ping, even when doing a full throttle 2-3-4 accleration.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.
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65CrewCabPW
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PostPosted: Mon Sep 12, 2011 12:30 am 
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Light dawns... No, it's not morning yet, though it feels like I've been doing this all night. Here is my theory. Because I have an 10.5:1 CR, with a relatively stock cam, pulling underhood air, I began to wonder if I was exceeding cylinder temperature required to self ignite the propane.

The answer is: On a hot day of 95 degrees F, with an underhood temperature of likely 130 to 140, plus heat gained from the exhaust and manifold.... I am likely to exceed 900 degrees internal cylinder temp on compression stroke, which may (will) ignite propane.

BUT, lower the air temperature to 60, reduce the underhood temp to perhaps 85, and the air temperature on compression stroke will never reach over 750, meaning it won't ignite until spark occurs. Which explains why, in cold night air runs, despite going "rich" and more advance, I have no pings and it runs great.

And it also explains why on a hot day while moving slowly, I can work the engine for less than 60 seconds and end up sounding like a diesel engine under the hood.

My plan of attack is as follows: Cold air intake setup to pull from in front of the radiator, remove exhaust heat and I think I will have no more issues with knock/pinging and also a LOT more power and better mileage, since i've been running at horrible timing (bad loss of power) trying to prevent 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.
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FrankRaso
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PostPosted: Mon Sep 12, 2011 12:17 pm 
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Joined: Fri Apr 16, 2004 10:50 am
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Are you sure that your compression ratio is actually 10.5:1? This isn't uncommon a CR for propane engines and I have not heard of anyone with this issue. However, if you find that supplying the engine with cooler air does make a difference, then having a cold air supply is a good idea.

Incidentally, the autoignition temperature for propane is 842°F and its critical compression ratio is about 12:1.

If you want to prevent exhaust heat gain, let me recommend Dutra Duals over headers.
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65CrewCabPW
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PostPosted: Mon Sep 12, 2011 7:22 pm 
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Quote:
Are you sure that your compression ratio is actually 10.5:1? This isn't uncommon a CR for propane engines and I have not heard of anyone with this issue. However, if you find that supplying the engine with cooler air does make a difference, then having a cold air supply is a good idea.

Incidentally, the autoignition temperature for propane is 842°F and its critical compression ratio is about 12:1.

If you want to prevent exhaust heat gain, let me recommend Dutra Duals over headers.
What I found for propane's auto ignition was 860 to over 1000, apparently depends on the other gasses mixed into the propane.

And yes, with very hot intake air, the compression pressure rise can easily exceed 900 degrees and under extreme conditions ( still real world and have encountered before ) exceed 1000 degrees.

We ran our calculations over and over and tried a dozen scenarios, and each of them corresponds to my observations about temperature, load, underhood temp, etc. So, I'm relatively confident this is at least part of the matter - a part that won't "fix" until it's fixed.

As for the Dutras... I'd love to, but the price is, well, I just can't do that. My funds have become extremely limited and there's a lot more stuff left to be done to the truck.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.
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65CrewCabPW
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PostPosted: Wed Oct 05, 2011 10:09 am 
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Well, here's an update: I ordered an Oregon Cams custom ground cam of

260 intake, 248 exhaust, .440 I .437 E, 108 CL, which I intend to run 4 deg advanced.

I have a cold air intake now, which breathes from in front of the radiator.

I'm going to try to get a 1 - 1.5 in carb spacer (matching the manifold holes) made by a machine shop to see if I can improve throttle response and torque.

ALSO: I found this : http://www.usgemini.com/Misc-Propane-Parts.html

First item is a flow control to limit the evap (converter) temperature to 130-140. It contains a reverse thermostat that allows flow until the temp reaches 130, and is supposed to be closed shortly after 130 degrees.

Hey, more info: https://www.altfuel.com/thermostats.htm

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