How to Convert Your Engine to Propane
There are 4 major components to a basic
propane fuel delivery system. They are listed below in order of fuel
travel. Fuel starts out in the propane tanks and ends up in the
engine. Click on the pics for larger versions.
This is where the LPG is stored under high pressure. When I say
high, I mean HIGH. You want these things stored where there is NO
CHANCE of them being punctured. Even though they are tough cookies
by design, who wants to deal with pressurized flaming bombs in their
4wd? By using two forklift bottles, I can use one up, close it off
at the tank, open the other one, and get someone to take the empty to
get refilled if I have to. It also serves as an early warning
system ... Warning, you are now down to half fuel capacity.
Bottles are one way to go, or you can get a regular tank which will
normally have a larger capacity. There are legality issues to
running propane in a vehicle though. You should read
here before you
choose which tank to go with.
Lockout Valve: Lockout
valves come in many different forms. Pressurized LPG goes straight
from the tank to the lockout valve through a high pressure line.
Their function is very simple ... SAFETY. The one seen in this
picture is a vacuum actuated lockout valve. It uses a diaphragm
attached to a valve and a spring with atmospheric pressure on one side
and vacuum on the other. The source of vacuum can be from anywhere
on your carb, really. When vacuum is applied, the diaphragm is
actuated opposing the spring, the valve is opened, and liquid propane is
allowed through. Without vacuum, no LPG gets through.
There are also electric lockout
valves. They use an electric solenoid to open a valve which then
lets LPG through. The power source could either be switched with
the ignition or manually switched. I used an electric valve until
it burnt out. I had it manually switched as a theft deterrent.
By hiding the switch, no thief would be able to start my Jeep up unless
they knew where to find the switch.
If you know enough about the
components of propane, you will know that this is not a required
component. You can run your high pressure LPG line straight to the
converter and it will work great. But if you have an older/used
converter like I do, or even a new one with a slightly faulty valve in
the converter, propane can leak out through your carb or converter.
Since propane is heavier than air, it will come to rest at the lowest
point in the vicinity and collect there. Then all it takes is a
small spark or flame to ignite an invisible bomb! So for $30 you
can avoid that problem altogether. Doesn't that seem worth it???
Converter: The converter
has a few different names that people call it. Converter,
regulator are three that come to mind. Most people don't realize
that this device actually does ALL of these tasks. As high
pressure LPG enters through the top, it is heated by the coolant lines
that you see entering through both sides of the top. By being
heated, it expands and is
into a gas, or a
vapor. The gas then passes through the device into a chamber
where it is
regulated down to about 4psi.
(About what your average grill uses.) The low pressure gas then
sits, waiting for vacuum to suck open another diaphragm. The more
vacuum (throttle) that is applied, the wider this diaphragm opens, and
the more gas is let through. At this point, the gaseous propane is
sucked into the carb/mixer.
You are looking at an IMPCO Model E
converter. You can see how all the bolts that hold it together are
flat head screws. Everything inside the converter is also
flathead, making only one tool necessary for a complete rebuild.
Cost of rebuild kit: ~$40! The Model E is supposedly good up
to ~325 hp, but people have reported using it all the way up to 400 hp.
This particular model features an electric choke, seen on the top of the
converter. The small tube coming out of the converter to the right
of the two wires would be a small hose going to the base of the carb.
If your engine needs to warm up to idle nice and perfect, you could hook
this up and flip a switch to apply power. A small, unregulated
source of propane gas would then flow to the engine, keeping the idle
clean during a cold start.
The second photo is from the lower
rear side of the mounted converter. The large hose coming out of
the bottom is the main fuel line going to the carb/mixer. It is
also the source of vacuum that actuates the large diaphragm inside the
Lockout & Converter: Here you see
a pic of my lockout valve connected directly to the top of the converter
/ regulator / vaporizer. I had the space to do it this way and the
double-threaded pipe fitting to do it with, so it made it easy. A HIGH
PRESSURE line could just as easily connect them if you needed them to be
in separate areas of the vehicle.
worth noting in the pic is the coolant lines running through the
converter. It doesn't really matter which one is in and out so long as
you have them both. They are important for two reasons. One is that,
as LPG expands into gas form, it absorbs heat from its immediate
surroundings. If the vehicle were run without the lines heating the
converter up, it would eventually freeze into a solid chunk of dried
ice. The vehicle will run for a little while, just not very long. The
second reason is that, in the process of removing heat, it cools down
your coolant. It's like having an extra little radiator! And if you're
like me, running a big V8 in a smaller vehicle with not much space for a
radiator, any added cooling is always welcome.
Carburetor: Last, and certainly
not least, comes the mixer/carb. What you see here is an IMPCO model
425 carb on top of a Holley Spreadbore throttle body. The model 425 is
rated at about 450 CFM and is the highest CFM offered by IMPCO.
Although there are higher CFM carbs made by companies like Technocarb,
the 425 is an industry standard and designed specifically for my
application, so it's hard to beat. If I desired a higher CFM I could
use dual carbs. If you're using a manifold that isn't made to fit the
Spreadbore base plate, you will need an adapter. I was using a stock
small block Chevy cast iron q-jet manifold and did need an adapter. I
had to slightly modify my throttle cable bracket to work with the
adapter. Since the Model 425 is made to be a direct bolt-in replacement
for Chevy 350's I was able to retain my stock throttle cable and
kick-down cable. Overall, installation of the carb is very straight
forward and easy. To find out how exactly a Model 425 works, click
Throttle linkage: Here you see a
few side pics of the carb's throttle linkage. You can see how my stock
throttle cable bolted right up. My kick down cable was about 1cm too
short, so I did what any good red-neck would do and bent a piece of coat
hanger in a loop to get my extra length and to attach it to the
linkage. In case you're wondering, it works fine. If you like manual
trannies, this won't be a problem for you at all.
Fuel Flow Diagram
This is how your propane setup should look when it is done. (Or a
variation of it.) There are actually computer-aided metering setups
that can be had for reasonable prices to increase mileage, but part of
the reason I was using propane was to get rid of computers, so that was
worthless to me. Obviously, since I did not use the computer, it's not
HIGH- PRESSURE LINE
Large low-pressure line
On to Final Impressions