OK, so here we are on a brand new thread. Thanks for sharing and the info and all. I have two questions:

1. Should a blue box Mopar electronic ignition with a Petronix flamethrower coil be enough for spark?

2. Would the two barrel or one barrel throttle body be better for the propane mixer? I can see the advantage of a bigger hole and therefore larger spread with the two barrel, but if I'm more concerned with a steady vacuum, a single barrel manifold might be best. I've got both.

Thanks,

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

A properly functioning ignition system should work fine with a propane system. Obviously, electronic ignitions are much better than points & condenser systems and are highly recommended. I'm not familiar with the blue box but any Mopar OEM standard or performance ECU should work fine. An HEI conversion would be fine too. A high performance coil like the Flamethrower would be a good idea too.

It's more important to use good quality caps, rotors, and wires so that the available voltage doesn't leak out or cross-fire. Cylinders that fire adjacent to one another (like #5 & #7 on V8's) should be well separated and not run parallel. To reduce the ignition's voltage demand, spark plugs should be gapped about 0.028" to 0.035" if a high energy ignition system is used. Since there is no cooling effect from the latent heat of evaporation of the fuel, spark plugs are commonly 1 to 2 heat ranges cooler with HD propane-only engines. Light duty passenger car conversions can use the same plug since a hotter plug requires less voltage.

As for which intake manifold to run, you should first decide upon whether you're going dual fuel or straight propane. If straight propane, you then have to decide which mixer to use and see which adapters fit the mixer to your throttle body. You could use either an Impco CA100 or CA125 mixer for a slant, with the CA100 better suited to the 170 and the CA125 to the 225. Impco no longer makes adapter AA3-89 (100 or 125 mixer to 1bbl Slant Six throttle body) so you would have to go with an AT2-4-1 throttle which fits the 1bbl's 1-1/2" SAE flange.

Impco no longer makes adapters to fit their larger (200, 225) mixers to Carter 2bbl carburetors either (AA3-45). You would have to use one of their throttle bodies for this as well.

As a much more expensive alternative, you could install the super-cool Technocarb 4bbl carburetor on an Offenhauser 4bbl intake. Their smallest standard size flows about 575 CFM. As a custom order, they could install smaller venturis so that it works properly on a slant six.

Dual fuel conversions are a bit more difficult since many adapters for the old carburetors aren't made anymore. The small dual fuel mixer (CA175) also appears to be discontinued. It would be difficult to mount it or the CA300 on top of the 1bbl carb since headroom is limited. Vialle makes a mixer that fits inside of the OEM air cleaner but I don't have any information about it. There are some other dual fuel options I've been considering but I haven't been able to try them out yet.

Frank--

You are a wealth of information. Today I talked with a guy in Austin who sells what he says are AFC mixers (but he's pretty secretive about them and says I wouldn't be able to find them under that name). They're pretty cool, and work like a motorcycle carb--long needle in a variable venturi. Of course this guy says that they are vastly superior to the Impco silicone diaphragm.

Any ideas about this???

Also, his belief is that there needs to be a foot or so between mixer and throttle body for better dispersion.

What say you?

Finally, he's saying that propane is much more affected by heat than gas, and that the air filter should be similair to a "cold air type" in order to get maximum effect. I'm a little unclear on this, because if propane has to be heated up to become a gas in the first place, why would you want it to be cooler?

Oh, and I'm figuring I might as well go all the way and make it fully propane.

Advice and wisdom much appreciated,

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

My guess is that the AFC mixer he's referring to is the OHG X-450 now known as the Woodward CA475. I'm not all that familiar with this mixer but Franz Hofmann indicates that it will work on 1.5L to 8.0L engines. As for which of the CA425 or CA475 is better, each has its advantages and disadvantages but the CA475 at least should work with slant-sized engines. The problem for a bolt-on conversion is the lack of adapters to fit the 1bbl or 2bbl intake manifold. Since the CA475 is a popular conversion for off-road 4x4s, it is readily available as a square bore 4bbl carburetor. I have no idea how well it work in practice on a slant.

As for putting the mixer 1 foot away from the throttle body, I've never heard of anyone doing this on purpose but, then again, there's a lot I don't know. My guess is that this extra plumbing would increase the Fuel Transport Delay and possibly make the engine more susceptable to backfires.

I think your guy in Austin needs to better understand how propane systems work. The converter is also known as a converter-regulator or a vaporizer. It works by first vaporizing the fuel (converting it to a gas) and then reduces its pressure from whatever it is in the tank to -1.5" WC (water column). The only reason heat is added to the fuel is that propane absorbs heat as it vaporizes. If the water flow drops too low or stops, the regulator starts passing liquid propane to the mixer. Since propane expands 270 times as it vaporizes, any liquid propane that gets past the regulator immediately causes the fuel mixture to become over-rich and this stalls the engine.

Why not just supply liquid propane to the engine and take advantage of propane's latent heat of evaporation? This would cool the fuel mixture like gasoline and overcome the slight loss in power of vapor systems. This is a great idea that is complicated by the fact that propane is a gas at atmospheric pressure. There is no way to control a boiling fuel with an ordinary carburetor. It's doable with fuel injection but the fuel would pick up heat from the engine and there would be no way to ensure that only liquid was being injected without constantly circulating the fuel back to the tank. There isn't a simple engineering solution to this and only within the last few years have the Europeans had success with liquid propane injection. But I digress.

Supplying the correct propane fuel mixture to the engine with a propane carburetor is far simpler. However, in an open-loop system, the mixer uses a gas valve to meter fuel to the air demanded by the engine. The gas valve's profile determines the fuel-air ratio at any given air flow and this is not load-dependant. This means that the fuel mixture for a highly loaded small engine could be the same as that for a lightly loaded larger engine. The open-loop gas valves are shaped to produce lean mixtures at low flows that become increasingly rich as the flow increases. Impco designed the shape of the gas valve for optimum mixtures for the mid-size engine between the largest and smallest displacement that the carburetor could be installed. They don't, however, say what is the optimum engine size for each gas valve.

If the converter were to get cooler water or less water flow, the vapor temperature would become lower as well. Since propane vapor is supplied to the mixer at a constant pressure of -1.5" WC, cooler fuel results in denser vapor that is still at a constant pressure. The net result would be a richer fuel mixture. So, although the fuel mixture supplied to the engine is fixed by the profile of the gas valve, supplying a warmer or cooler vapor to the mixer will change the actual fuel mixture delivered to the engine.

Lean mixtures result in better fuel economy while cruising on the highway and slightly rich mixtures result in better power for acceleration. All commercially available feedback systems produce stoichiometric (chemically correct) fuel mixtures for reduced emissions. While an open-loop system could potentially have better fuel economy if it is set up properly, a closed-loop (or feedback) system would produce consistently good fuel economy. An open-loop system is inconsistent because its fuel mixture is also somewhat dependent upon water temperature. If you make a lot of short winter trips with an open-loop system, your fuel economy will not be as good as summer long distance highway driving.

The amount of power produced by the engine depends upon the number of oxygen molecules that can be trapped inside the combustion chamber. The denser the air getting into the cylinders, the more power your engine will make. Exactly the same as gasoline. Since there no need for other devices like air preheating and intake manifold hot spots to ensure that the fuel is vaporized and properly distributed to each cylinder, a propane engine should get the coldest air possible. This helps to overcome the slight loss in volumetric efficiency from the gaseous fuel displacing some of the air reaching the cylinders.

Frank

The trunk area where there spare tire well and fuel tank is located on an A-body doesn't lend itself to a propane fuel tank. Unless you make some major modifications to the sheet metal in this area, the only practical location for the new propane fuel tank is on the shelf area above the axle. Since the gasoline tank could easily remain in place along with the fuel lines and fuel pump, a dual-fuel conversion would not take up any more space than a straight conversion.

The reason I mention this is that I believe that there are other dual fuel options than the Impco Model 300 and 175 mixers. Since these options aren't commerically available as a kit, I have to call them experimental options. There are two ideas that I've been thinking about if you're up for some R&D.

IDEA 1
Using the MegaSquirt ECU for propane injection would allow you to run optimum fuel mixtures and ignition curves for both fuels and the added expense of the injectors and MS ECU could pay for itself in improved fuel economy. I'm trying to verify whether the 3-ohm injectors would work properly with the MS system. I have no idea what the payback would be, however. The system would look a bit like this:


IDEA 2
I think it would be relatively simple to do a dual fuel conversion by installing a propane venturi underneath either a 1bbl or 2bbl carburetor. This propane venturi would look a bit like an ordinary carb spacer except that there would be a fuel inlet or two on the spacer. The fuel mixture would be controlled with feedback system using a stepper motor operated fuel valve, which looks like this:


A similar (& I believe still available) Vialle system that uses a venturi plate mounted on the air horn looks like this:

Frank!

Thanks very much for the tips and tutelage. I may join up with the forum you cited.

So at this point an Impco 125 with the computer and a cold air induction looks like the best compromise for me. I'm still getting $$ together to do the whole thing.

appreciatively,

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

If you are really going to go through with this setup I would suggest having the dual fuel setup.

I used to work for a propane company back in the 70's and had a 72 Fury II doing dual fuel. Works great, but I had access to propane fuel 24/7. Will you?

Don't get caught without having some way to get home. It was great to just flip the switch and pull a small cable to switch as you drive. I used to get over 500 miles before being forced to fuel up. Messed with a lot of my friends to see me do it too!

At least I had a choice of which to put in. I only ran out once. I was at a customers place and borrowed a forklift tank to get me home.

brings back memories.
thanks for you starting this post.

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67 Dart GT convertible
"225 Slant 6"
Super 6 and 2.25" exhaust.

On an earlier topic (Shaving Head--increasing compression), starting propane engines in cold weather was brought up. I thought it would be more appropriate to further address that issue in this topic.

My winter car is a straight propane conversion and I have absolutely no problems starting my car in cold weather. To illustrate that point, I made a short video of a cold start when we had a -18°C/-0.4°F morning on February 15th:
http://www.youtube.com/watch?v=74CqA71DmRA

When people say that their car runs a lot better when it's warmed up, they are unknowingly referring to their warmed up intake manifold. Gasoline vehicles need to get a vaporized fuel mixture evenly distributed to each cylinder to have a smooth running engine. This is why chokes and intake hot spots are so important for carbureted cars. Since a propane carburetor supplies only propane vapor, the engine will run smooth in extremely low temperatures as long as the converter has enough water flow to produce propane vapor. My experience has always been that if it'll crank, it'll start.

I thought I should throw my experience from yesterday in there.

After spending the day working on a friends VW jetta in vain, I was tired and in need of some feeling of success. So I grabbed the ebay propane bits, Impco 225 carb, model E evaporator and bolted them to my 170cu valiant. The 225 carb I got bolted right to the 2bbl adapter that came on my clifford intake. After 15min of removing the weber, bolting the Impco assembly on, and attaching the BBQ tank, I was ready to make noise. To my surprised, my cheeseball setup worked wonderfully. Now this was just a static test, as I could not drive it with the propane just sitting on a 5gal paint bucket next to the passenger fender (now if I only had that old skate board...). I have never heard this engine start so fast, idle so smooth, and free rev so well. Mind you, this is with a vapor only feed from the bbq tank, no water cooling on the vaporisor (no need as it was only vapor), no tuning (no idea what it came off of)... I am very encouraged so far.

Another interesting tid bit, I didn't have a gasket, too lazy to make one, and out of permatex #1. First thought was crap, no fuel stable sealant on hand. Then I realised, propane will not disolve houshold caulking, which is what i used for the test. Retarded, but true..

Don't worry, this was only a test, and one that was pressured by the quickly fading sun light. I will set this thing up right before I drive it.

mh-

Good work with the temporary conversion! Oversized propane carbs tend to have starting problems and poor low speed drivability. The Model 225 is little oversized for the 170 so you did very well getting it to start so easily.

BTW, water is actually needed to heat the liquid propane so that the engine gets a continuous supply of vapor. The BBQ tank depends upon heat transfer from the air to the tank to provide enough heat to vaporize the fuel. While the tank may be able to vaporize enough fuel to allow the engine the idle, there is no way it can keep up an automotive engine under load. Next time you start it, rev it up and watch how fast the BBQ tank regulator frosts up.

Yea I expected the tank to frost, but it didn't during the ten minutes or so it ran. I didnt drive it, so it saw no load, just idle to 6k reving.

It will be set up right bofore its driven.

mh-