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Natural Gas powered 343???

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Skwishy View Drop Down
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    Posted: Aug/06/2022 at 12:14pm
I posted something about this in general. But i figured id put it here too! A recent parts car i picked up has some sort of early 70s natural gas system. Any ideas on this thing? Its also got a HUGE 20 gallon lp tank in the trunk. like it spans from quarter panel to quarter panel. Pretty cool stuff
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Heavy 488 Quote  Post ReplyReply Direct Link To This Post Posted: Aug/06/2022 at 12:20pm
Octane numbers comparable to leaded race fuel and burns clean
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Aug/06/2022 at 12:25pm
That's likely Liquid Propane (LP) and not natural gas.
There was a couple of companies that had conversion kits here back in the 70's. Did a few farm trucks at my first place of work. Lada's came from the factory with LP systems then.
All was well until our government decided on yearly inspections and certified installation/repair people. Then it became too much of a hassle and vanished.
Cool find though!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote purple72Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: Aug/06/2022 at 12:27pm
Originally posted by Heavy 488 Heavy 488 wrote:

Octane numbers comparable to leaded race fuel and burns clean
and because it burns clean oil lasts much longer and the engine doesn't wear like it would on gas. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Skwishy Quote  Post ReplyReply Direct Link To This Post Posted: Aug/06/2022 at 2:00pm
Does anybody want this stuff? Its free to whomever needs it
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mr_Roboto Quote  Post ReplyReply Direct Link To This Post Posted: Aug/06/2022 at 2:05pm
OK, do you have a Century or an Impco? I probably still have an Impco book here somewhere. There's a few things worth knowing about these:
-The piece on the left in the engine bay (about 4" tall, about 7" diameter) is the vaporizer. It should have some water lines coming in and out of it. 
-That corrugated hose should go to the "carburetor" which is a demand based system to feed the vaporized propane to the engine. I think you're missing a lot of it, but that the piece in there is part of it. Some times they would run "dual fuel" and have it where they'd be able to switch between propane and gasoline.
-There's a solenoid at the front right of the engine, that may be the fuel lock out for a dual fuel system. There's a bigger solenoid on the right behind the vaporizer that may be the LPG one.
-Controls inside will likely be a push button to "prime" the system when cold and a switch to go between gasoline and propane.
-There may be a box for the ignition system that is used to advance the timing to run propane. As mentioned it's high octane. 

The sticker on the back says "DPL." Something power and light?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SC397 Quote  Post ReplyReply Direct Link To This Post Posted: Aug/06/2022 at 2:14pm
LP AMC's and Jeeps were not uncommon in Mexico and Brazil among other places.
I burns ultra clean but there is a 25/30% power loss with propane.
Back in 1974-76 I worked for a gas company and all of their service trucks and equipment was converted to LP as soon as they got them.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mr_Roboto Quote  Post ReplyReply Direct Link To This Post Posted: Aug/06/2022 at 2:38pm
Originally posted by Skwishy Skwishy wrote:

Does anybody want this stuff? Its free to whomever needs it

Where in Wisconsin are you? Probably hoarding but I wouldn't say no if you're close. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Skwishy Quote  Post ReplyReply Direct Link To This Post Posted: Aug/06/2022 at 4:58pm
It is a century imperial 300a 
Dual fuel system it has the senoid on the fuel line to switch between. I live in green bay
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Aug/06/2022 at 6:56pm
Propane (LPG) conversions used to be quite popular in Australia and at one time you could even buy some new cars with dedicated propane only fuel systems from the factory. This was largely driven by propane being much cheaper than gasoline, partly because it didn't attract fuel excise, so typically half the cost or less than gasoline. However over time the cost of propane has increased and the government has added excise tax to it as well, so its now around 75% of the cost of gasoline. As mentioned above, you typically burn 25-30% more on a volume basis, so there is no longer any real financial benefit to run it that would justify the expense of installing a system in your car. Filling stations are also getting few and far between due to the lack of demand.

The Century and Impco systems are essentially designed for forklifts, so they aren't really big enough for any serious performance applications, although there were a few people who ran twin mixer setups, but for the most part people were looking to save money on fuel and not focused on the added performance potential of Propane. We did have a company called Gas Research who made some performance propane throttle bodies and to get the most out of the fuel you really need to build your engine around it with higher compression as well as cam and timing changes. 

Dual fuel systems are generally pretty average because they are a compromise and never really optimized to give the best on either fuel. My 69 Javelin had a dual fuel system on the 4V 343 when I got it, but I ended up taking it off for this very reason and went back to gasoline when I was building the motor for more performance. The good thing is they never cut a hole in the rear quarter panel for the propane filler, which was pretty common back in the day.

We have a few complications here as only a licensed gas fitter can legally work on the system, no DIY, although I'm sure some do (not me of course Wink), but installation of the system does need to be approved by our licensing department and needs a modification plate from the installer to be attached. Legally, the cylinder needs to be recertified every ten years, which costs nearly as much as a new cylinder. 

On the safety side as well as the solenoid valves, you should also have some sort of ignition safety switch which cuts the fuel off when there is no spark.

Unless there is some significant cost benefit to running propane where you are, I would bin it, the cylinder is probably well past its use by date and the rest of it looks pretty dilapidated.

EFI is a much better option these days.


Edited by WesternRed - Aug/06/2022 at 7:02pm
I've finally given up drinking for good...........now I only drink for evil.
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