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Old 12-19-2004, 11:35 PM
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Propane

Hoping someone could help a guy out. My brother has a 1979 Ford 1/2 ton pickup with a 400 and a 4 spd. It weighs prolly over 5000 lbs cuz it has a heavy flatbed on it. This pickup is a beat around truck used for hunting and doesnt see much over 4500 rpm. The 400 is run on propane and it is time for an overhaul. I was wondering of what kind of cam we could run for some low speed torque and some other helpful power hints by running propane. Maybe a more general question of how can we get some decent power out of this propane burner. Hope this question isnt too broad?! Thank you.

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Old 12-20-2004, 09:42 AM
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my advise would be to put what is called an industrial cam in it it will provide the low end your looking for and has no rough idle . ive put a lot of these in older farm trucks for some of the local farmers around here and they have really been impressed with the extra tourqe they get
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Old 12-20-2004, 11:37 AM
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Propane loves compression. If you are running strictly propane, I'd bump the compression, some. Make it a little meaner huntin' rig.
Don't forget stelite, or better valves, and hardened seats. Propane is very dry, and will cause valve seat recession, if the proper steps aren't taken.
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Old 12-20-2004, 12:54 PM
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propane

His 400 M is a 79 block so it has hardened valve seats, so errosion shoudnt be a serious problem.
Id like to know what the optimum compression ratio would be for running propane. The stock 79 400 has a compression of 8:1.
The cam is a 192/198 degree, .427/433" lift and a 110 degree lobe separation. This is to my knowledge, the only cam that was put in the 400M, and for industrial use, it was advanced quite a bit for the lower rpm torque improvement.

The biggest problem with the Cleveland valve is that they are a two piece unit and using hi tension valve springs has a tendency to pull the head off of the stem. going with stainless one piece valves is definately a benefit, both in engine longevity and valve life, itself.
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Old 12-20-2004, 04:32 PM
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I'll agree that the factory hardened valve seats normally hold up to moderate use on propane but I would replace them with hard seat if there is any sign of seat recession. You never know how deep the factory hardening goes.
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Old 12-20-2004, 05:13 PM
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hardened seats

Not sure about other brands but, when Ive had hardened seats replaced in Ford engines (not a common event), the seat is a special hardened steel ring which is press fit into a seat that is cut around the throat of the runner. These seats are about 1/4" X 1/4" X 1 3/4" OD X 1 1/2" ID on a small block ford.
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Old 12-20-2004, 06:28 PM
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What kind of propane carburetor does the truck have on it? There are some models that are pretty restrictive and tend to kill the power. I would recommend running at least a 425 impco or M&M's(Ak Miller's ex wife owns the company) better version. On your cam stay small duration and higher lift, (basically an RV cam) I had a truck with a 108* cam that ran pretty well. Propane likes a lot of initial timing(16*) and will work better with higher compression (as a couple have already recommended) I wouldnt go higher than 11:1. I have had several of these engines(351m-400) on propane and didnt have any problems with the stock exhaust seats (100,000+ miles).

If your wanting alot of low end you might want to think about putting a 460 in in place of the 400. It is a pretty common swap. There are more parts available for the 460. If not I seem to remember 4jaw had a 400 he made into a decent runner.

Hope this helps

John

Last edited by propaniac; 12-21-2004 at 08:25 AM.
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Old 12-20-2004, 06:32 PM
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Here is a little discussion a few weeks ago on the subject.
http://hotrodders.com/showthread.php...hlight=Propane
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