Adapt Your Automobile Engine For Ethyl Alcohol Use
Now that we've explained
the fundamental differences between alcohol and gasoline fuels, we can
get on with the actual conversion of a conventional gasoline-burning
engine to alcohol use. We'll cover the three major changes (main jet,
idle jet, and timing), and we'll also go on to cover some other areas
that may be of interest to those who want to go further to increase the
efficiency of their alcohol-burning engines.
The first thing you'll
have to alter is the main metering jet in your carburetor. In most
carburetors, this is a threaded brass plug with a specific-sized hole
drilled through the center of it. This hole is called the main jet
orifice, and its diameter dictates how rich or lean the air/fuel mixture
will be when the car is traveling at cruising speeds. Naturally, the
smaller the hole is, the less fuel will blend with the air and the
leaner the mixture will be. As the orifice is enlarged, the mixture gets
Since alcohol requires a richer air/fuel ratio, it's necessary to bore
out the main jet orifice when using ethanol fuel. The standard jet size
in MOTHER's alcohol-powered truck was .056" ... in other words, this was
the diameter of the jet orifice. In order to operate the engine
successfully on alcohol fuel, it's necessary to enlarge this opening by
anywhere from 20 to 40%.
Start your conversion by gathering all the tools and hardware you'll
need to complete the job. A screwdriver, an assortment of end wrenches,
visegrip pliers, a putty knife, a pair of needle-nose pliers, and a
power drill - with bits ranging in size from a No. 51 (.067") to a No.
46 (.081") are usually all you'll need. To make your job easier, though,
you might want to refer to a Motor, Chilton, or Glenn auto repair manual
for exploded illustrations to guide you through the necessary carburetor
disassembly and reassembly. (A second alternative would be to purchase a
carburetor rebuilding kit for your make and model car ... which will not
only supply you with a working diagram, but provide gaskets, seals, and
other parts that may get damaged during the stripdown process.)
You may also need to purchase several main jet assemblies from your auto
dealer (if the carburetor you're converting has a removable main jet),
since you'll probably want to experiment with different air/fuel ratios.
In order to take the carburetor apart, you'll first have to remove its
air filter housing and all its hoses, tubes, and paraphernalia from the
engine. Then disconnect the throttle linkage from the engine and any
choke linkage rods that aren't self-contained on the carburetor body.
(If you've got a manual choke, remove its cable and tie it out of the
You'll also have to unscrew the fuel line from the carburetor inlet
fitting and remove any other hoses that fasten to the unit, including
vacuum and other air control lines.
When the carburetor is free from all external attachments, remove it
from the manifold by loosening the hold-down bolts at its base, and turn
the unit upside down to drain out any gasoline that may be in the float
bowl. Remove the carb's air horn (you may have to unfasten the choke
stepdown linkage rod) and locate the main jet. (Some carburetors have
the jet installed in a main well support, while others mount the brass
fixture right in the float bowl body.)
Once you've removed the main jet, you can prepare to enlarge it. First
measure the diameter of its opening by slipping a drill bit of known
size into the hole (this bit should fit snugly, of course). In some
cases, the size of the jet is stamped in thousandths of an inch right on
its face, so you don't have to go to this trouble. When you know what
the standard jet size is, you can calculate the additional enlargement
necessary to operate the engine on alcohol.
For example, MOTHER's truck originally had a .056" main metering jet. In
order to increase that opening's diameter by 40%, we first had to
multiply .056" by .40 (which yielded .022"), then we had to add that
additional .022" to the original .056" ... this figured out to a total
diameter of .078". The nearest size drill bit to this is a No. 47, which
is .0785" in diameter ... this was the bit necessary to bring the jet to
40% over its original size.
Hold the jet with your vise-grips and carefully bore out its central
hole (if possible, use the jetholding body of the carburetor itself as a
mount while you drill). Be sure to do your drilling as nearly straight
as possible, and clean any brass residue out of the carburetor and its
components after the operation is over.
There are some carburetors that do not use fixed-size jets alone, but
also utilize what is known as a "metering rod". This is usually a thin
tapered or stepped brass rod that's suspended within a brass jet
orifice, which may or may not be removable. The fuel is, in this case,
drawn through the space between the rod and its brass "housing".
Depending on how far the throttle is opened, the metering rod is lifted
out of the hole ... and - since the rod is thick at its "base" (near the
top), and progressively thinner at its tip (toward the bottom) - the
farther it's drawn out of the hole, the more fuel is allowed to flow
between the central rod and the opening.
The conversion on this type of metering system is basically the same as
the fixed-jet conversion. To enlarge this orifice, you can either remove
the metering rod and very carefully drill out the brass jet (take it out
of the carburetor if it's removable), or take the tapered brass rod to a
machine shop and have it turned down slightly (the same effect can be
accomplished less accurately by sanding the rod down with emery cloth).
If you choose to drill the jet to a larger dimension, the diameter
should be increased anywhere from 10 to 32%.
With the fixed-jet type of carburetor, the diameter of the jet orifice
can vary from about 20% over standard to 40% larger - or even more -
depending on the engine's size, its compression ratio, and the vehicle's
weight. Probably the best way to determine what is right for your needs
is to experiment, since many instruments used to measure the proper
air/fuel ratio don't register correctly when the engine is burning
By planning on a diameter enlargement of anywhere from 35 to 40% at
first, you'll be perfectly safe, since the engine will tolerate this
size easily. If you go too much larger than this, you'll probably just
be wasting fuel. On the other hand, by going too small, you may find
that you'll lose power ... or even worse, that you may burn valves
because of an overly lean mixture.
On the other hand, it is true that a lean mixture - to a point - will
result in improved economy with hardly a noticeable loss in performance.
With MOTHER's vehicle, the absolute limit was a 19% enlargement in jet
size ... although the truck does run slightly better with a 25%
larger-than-standard main jet. You may find, as we did, that your
vehicle performs well with a smaller jet opening than the suggested
35-40% increase but to be on the safe side, periodically check your
spark plugs, especially after an extended drive. If they are white in
color, or otherwise appear to be subject to excessive heat (look for
hairline cracks on the center electrode's insulative jacket), this is an
indication that your engine is burning too lean ... and the jet must be
IDLE ORIFICE CHANGES
Most carburetors will
require additional idle circuit enlargement in order for the engine to
run at slowest, or idle, speeds. This is because the circuit that's fed
by the main jet operates fully only when the throttle plate within the
throat of the carburetor is opened past the idle position. When the
plate is in the idle position, the air/fuel mixture is allowed to enter
the manifold only through the idle orifice itself ... which, if it isn't
large enough, will not provide the needed amount of air/fuel blend to
keep the engine running.
On some engines, it may only be necessary to loosen the idle mixture
screw at the base of the carburetor in order to provide the correct
amount of fuel, since this threaded shaft has a tapered tip which allows
more mixture to pass as the tip is backed off. On other engines, it's
possible that the seat itself, into which the tapered screw extends,
must be enlarged in order to accomplish the same thing.
In most cases, if the seat has to be bored out, it can be enlarged by
50%, using the same method of measurement as was detailed in the main
jet section. This will allow a full range of adjustment with the idle
mixture screw, even if you should want to go back to gasoline fuel.
(When drilling, be careful not to damage the threads in the carburetor
As a precaution against the idle screw's vibrating loose from its
threaded opening, you can shim the idle mixture screw spring with a
couple of small lock washers ... this will prevent the screw from
turning even if it's drawn out farther from the seat than it normally
POWER VALVE CHANGES
Most modern auto
carburetors have what is known as a power valve that allows extra fuel
to blend with the air/fuel mixture when the accelerator is depressed, in
order to enrich the mixture under load conditions. This
vacuum-controlled valve is spring loaded, and shuts off when it isn't
needed in order to conserve fuel.
The power valve used in the carburetor illustrated is somewhat difficult
to alter and, besides, is sufficient for alcohol use in its normal
configuration if it's working properly. However, there are other
carburetors - specifically the Holley and Ford (Autolite or Motorcraft)
brands - that have easily replaceable power valves which are available
from auto parts stores in various sizes. If you use a power valve with a
25% or so greater flow capacity than the one that originally came with
the carburetor, your air/alcohol mixture will be sufficiently enriched
when your engine needs more power.
ACCELERATOR PUMP CHANGES
In addition to a power
valve, almost all automotive carburetors utilize an accelerator pump.
This is a mechanically activated plunger or diaphragm that injects a
stream of raw fuel directly down the throat of the carburetor when the
accelerator is suddenly depressed. The fuel is injected through a small
orifice located in the throat wall at some point above the carburetor
venturi (the point at which the throat narrows).
The reason the accelerator pump is incorporated into modern carburetors
is that as the accelerator is pressed and more air/fuel mixture is drawn
into the cylinders, some of the liquid particles in the blend tend to
stick to the walls of the intake manifold, effectively leaning out the
mixture by the time it reaches the combustion chambers. The extra squirt
of fuel that's added by the accelerator pump makes up for this initial
In order to adapt your accelerator pump to use alcohol effectively,
you'll probably have to enlarge the size of the injection orifice
slightly (anywhere from 10 to 25% is fine ... if you go larger than
that, you'll risk the possibility of altering the pump pressure enough
either to turn the fuel stream into a dribble or to empty the pump
reservoir before the pump has made a full stroke).
As an alternative to enlarging the hole, you may be able to simply
adjust the stroke length of the pump arm in order to feed more fuel.
Most carburetors installed on Ford products already have a provision for
seasonal adjustment, so it's just a matter of putting the pump on its
richest setting. Other carburetors, too, have threaded rods that can be
adjusted to accomplish the same thing.
Although it's not
absolutely necessary to adapt your car's choke system to burn alcohol
fuel, it has been our experience that a manually operated choke is more
desirable on an alcohol-powered car. If your vehicle's engine is already
so equipped, fine. If not, you can purchase - for about $7.00 from any
auto parts store - a manual choke conversion kit that will allow
virtually any automatic choke to be adapted for manual control.
In order to take advantage
of the great antiknock qualities that alcohol fuel provides, you'll have
to advance the engine's ignition timing by turning the distributor
housing opposite to the direction in which the rotor spins (the housing
is held in place by a bolted clamp).
Normally, an engine using gasoline has its timing set so the spark
occurs at anywhere from 8 deg BTDC (Before Top Dead Center) to TDC (Top
Dead Center). Since alcohol has a higher "octane" rating, you can
advance the timing considerably more than this. (In the case of MOTHER's
truck, we adjusted it to operate at approximately 22 deg BTDC without
any sign of pre-ignition, even under load.) Of course, care should be
taken when you adjust the timing on your vehicle, since a 22 deg advance
might be excessive for your car. Remember, it's not safe to be just
short of detonation, since inaudible knocking can also damage the engine
... the best procedure is to set the distributor timing at least two
degrees retarded from the point of detonation.
COMPRESSION RATIO CHANGES
Increasing the compression
ratio of the engine will be impractical for most people, because of the
expense and work involved ... however, this modification will do a great
deal to improve engine performance and economy. Just like a timing
advance, a compression ratio hike will take advantage of the potential
that alcohol has to offer as a fuel. Optimally, the ratio can be
increased to 14- or 15-to-1 ... but even a nominal increase - to perhaps
12-to-1, a figure that some manufacturers have already offered in the
past for premium gasoline use - will result in a vast improvement over
the standard 8- or 8.5-to-1 that most manufacturers incorporate into
their engines today.
If you intend to convert an automobile that already has a compression
ratio of 10-to-1 or better, it probably won't pay to make any internal
changes. However, if the engine you're considering needs an overhaul, it
would be wise to modify it regardless of its compression ratio.
The most inexpensive way to increase your compression ratio is to
install a set of high compression pistons. The forged units are designed
to pack the air/fuel charge tightly into the combustion chamber for
increased power, and have special relief notches built into their heads
for valve clearance. Be cautioned, however, that some engines may not
tolerate a 15-to-1 compression ratio with standard connecting rods and
bearings ... these components, too, may have to be replaced with
high-strength competition grade parts.
Another way of increasing compression ratio slightly is by "milling''
(planing) the surfaces of the cylinder head and/or block. With some
engines, this may result in only a 1/2-point ratio increase ... with
others, slightly more. It would be best to check with your local engine
rebuilder or automotive machine shop to determine exactly what you'll
gain with your particular model engine before you go to the trouble of
A third - and perhaps the most versatile - way of effectively increasing
the compression ratio is by installing a supercharger or turbocharger.
These units, although ranging in price from $800 to over $1,200, provide
a pressure boost in the combustion chamber proportional to the engine's
RPM. Hence, compression would not be excessive during engine start-up as
it would be with the other methods.
You should encounter no problem with a severe compression ratio
increase, unless you decide to switch back to gasoline fuel ... and in
this case, you could install a water injection system that would allow
you to operate the car even on regular fuel without fear of detonation.
In extremely cold
climates, it may be necessary to preheat your alcohol fuel before it
enters the carburetor float bowl. This can be accomplished easily by
splicing into the fuel feed line - near the point where it passes the
upper radiator hose - and installing a fuel heater at this location.
You can fabricate a fuel heater in a matter of minutes by first locating
a 5" section of copper or other metal pipe with an outside diameter
equal to that of the inner diameter of your upper radiator hose. Then
find several feet of soft copper tubing that will slip snugly inside
your fuel feed line. (If your fuel line is steel, you'll have to cut it
and splice in two short sections of the appropriately sized neoprene
hose.) Wrap the soft tubing several times around the middle of the large
pipe section (the number of coils depends on how warm you want the fuel
to become, but anything from three to eight wraps will suffice), and
solder it in position if possible.
To install the unit, just clamp it in place between the existing
radiator hose and another short section of hose connected to the
radiator neck, and attach the fuel line to the inlet and outlet of the
copper coil. As the engine reaches operating temperature, the hot water
flowing through the engine's cooling system will heat the coils and the
fuel passing through them.
Most trucks and autos have
air filter housings which are designed to allow heated air from around
the exhaust manifold to channel through a duct and enter the carburetor
when the engine first starts from a cold state. As the engine warms up,
a flap within the air cleaner "snorkel" shuts off this supply of warm
air and allows ambient air from the engine compartment to enter in its
This flap is usually either thermostatically or vacuum controlled ...
but either way, you may find it helpful during the winter months to
leave this valve closed to the cold outside air. This can be done either
by disconnecting the bimetallic thermostat spring that controls the flap
and installing a small spring of your own that will hold the valve in
the required position, or - if the flap is vacuum activated - by
connecting an existing permanent vacuum line to its control fitting.
(You can, of course, remove the control line entirely, plug it up, and
hold the flap closed with a spring if you wish.)
In order to get maximum
efficiency from your engine, you may need to change the thermostat
within the engine block. Thermostats are available in various heat
ranges from 140 to 200 deg F, and these temperatures indicate how hot
the engine coolant will be allowed to get before the thermostat opens to
initiate the cooling process. (A thermostat is designed to hold the
coolant within the cylinder head till it achieves the desired
temperature ... at which point the heated liquid is allowed to escape
into the radiator to be cooled, and is replaced by a fresh supply of
cool fluid. Depending on the engine's operating conditions, the
thermostat may cycle open and shut regularly over the span of a few
If the water in your vehicle isn't getting warm enough to provide hot
air through the heating system, you should replace the thermostat with a
higher-rated unit. By the same token, the intake manifold of your engine
should be warm to the touch when burning alcohol. If it's cold - or iced
over - the alcohol most likely isn't being given a chance to vaporize
sufficiently, and therefore is not being used efficiently. By using a
hotter thermostat, you'll be able to warm up the entire engine,
including the intake manifold.
COLD WEATHER STARTING
Since alcohol doesn't
vaporize as easily as does gasoline, cold weather starting can be a
problem ... especially if the engine itself is cold. To alleviate this
undesirable situation, MOTHER's research staff has designed a
combination coldstart/dual-fuel system that'll work with any car.
All it requires is a five-gallon fuel storage tank with a fuel filler
neck brazed into its top (we used an old propane bottle), an auxiliary
electric fuel pump, some steel brake or fuel line, neoprene hose, an
elbow, a length of copper pipe, a small metering jet, and several needle
valves, tees, and hose barbs. (Details and illustrations of the
installation are shown in the article reprints from MOTHER NOS. 59 and
60, which are included in this workbook.)
The five-gallon tank is mounted in some safe place on the truck or
automobile and used to store gasoline. This cache of petroleum fuel
serves a dual role: When it's needed for cold starting purposes, the
electric pump is activated momentarily from inside the car and a fine
stream of gasoline is injected down the throat of the carburetor. And,
in the event that your alcohol supply is unexpectedly depleted on the
highway, the gasoline stored in the small tank can be routed into the
carburetor normally for emergency use.
INITIAL USE OF ALCOHOL
An engine altered as
outlined in this chapter will run well on alcohol. Nonetheless, there
are certain things to be aware of as you begin to make use of the new
fuel. First, remember that the alcohol will act as a cleansing agent ...
and - as such - will not only clean out your tank, fuel lines, and
filters, but will also purge your engine's internal parts of built-up
carbon, gum, and varnish deposits.
In effect, what this means is that suddenly a lot of filth will be
floating around in your fuel ... and it may be enough to clog your fuel
filter to the point of not allowing any fuel to pass. By the same token,
loosened internal engine deposits can foul the spark plugs badly ... so
if your vehicle begins to function poorly soon after your conversion,
check these two areas first.
In addition to the fact that alcohol is a cleaning agent, it is also a
solvent ... and this means that certain types of plastics used in the
fuel system of your vehicle may be attacked by it. Actually, most of the
plastics deterioration problems associated with ethanol fuel are caused
by the substances used to denature it - such as acetone or methyl ethyl
ketone - rather than the alcohol itself. If you manufacture your own
alcohol and denature it with gasoline, as federal regulations now
permit, deterioration problems will be reduced to a minimum.
Most vehicles manufactured prior to 1970 used stainless steel or brass
components in their fuel systems ... hence there is little chance of
parts failure. In cars that use plastic components, however, there are
several areas of potential deterioration:  Within the fuel tank, both
the float and the strainer on the fuel intake tube may be plastic ...
replace them if necessary.  The fuel lines themselves - if they are
the clear, flexible type - may also soften ... you can install neoprene
hose in their place.  The fuel pump diaphragm may also be subject to
failure ... either replace it with a piece of spring steel, or replace
the entire pump with an electric gear-type model available from your
auto parts store. (Jaguars and Alfa-Romeos also use all-metallic pumps
if you're willing to pay the price.)  Plastic in-line fuel filters
should be replaced with metal ones.  Many modern carburetors use
plastic float needles, seals, and floats ... you can usually purchase
the equivalent carburetors - but ten years older - from an auto wrecking
yard for about $5.00. These should contain metal components, and can be
salvaged for parts.
Of course, not all plastics are subject to corrosion, and neither are
all types of rubber. Generally, butyl rubber (like the type used in
inner tubes) should be avoided. Neoprene, however, holds up well even at
higher temperatures, and might only present a problem (because of
swelling) if it's used as a tip on carburetor float needles. Automotive
plastics vary greatly in their composition ... the
table below indicates the performance of various types of plastic
One final thing to be aware of when burning alcohol in your vehicle is
that the new fuel does not contain the additives which the engine has
become used to over the years ... specifically the leads which help to
lubricate the valve seats. Of course, any car built in 1975 or later is
already equipped with hardened valves and seats, so there should be no
problem with them ... but even vehicles of other years (with the
possible exception of large-block 1972-1974 Ford products) can tolerate
alcohol fuel safely.
One reason for this is that water in the alcohol acts as a "cushion" and
lubricant for the valves ... but if you are still wary of using alcohol
fuel in its pure form, you can add up to 1% kerosene or diesel fuel to
your alcohol supply. This will provide the lubrication of petroleum
fuels with a minimum of pollution.
FUEL INJECTION SYSTEMS
Since some vehicles are
equipped with fuel injection rather than carburetors, we will briefly
touch on the use of alcohol with that system. There are two important
factors in a fuel injection setup: injection timing and control jet
diameter. Fortunately - since many systems now use an electronically
controlled timing sequence - injection timing is not critical in a fuel
injected engine. Neither performance nor economy improve substantially
by either advancing or retarding the injection timing process.
Control jet diameter, on the other hand, is an important factor. If you
increase the size of the control jets (which are the equivalent of the
metering jets in a carburetor), the engine will operate well on alcohol
fuel. An increase of 15-20% is all that's necessary to accomplish the
conversion. (Ignition timing should, of course, be advanced as explained
An interesting feature of the fuel injection system is that it doesn't
require any gasoline during the cold weather starting process to fire
the engine up. Since the fuel is injected at a pressure of about 250
PSI, the alcohol fuel is sufficiently vaporized to ignite easily within
the combustion chamber.
Because of the fact that
diesel engines do not use conventional spark ignition systems, it's
difficult for pure alcohol to ignite within the combustion chamber.
This, coupled with the fact that diesel injector pumps won't tolerate
water, could be a problem ... especially if the alcohol used was not
Fortunately, there are several other ways to utilize homemade ethanol in
a diesel engine by introducing vaporized alcohol to the engine along
with diesel fuel. Probably the simplest way is to mount an automobile
carburetor right on the diesel's air intake manifold and supplement the
diesel fuel with alcohol metered through that piece of equipment. Of
course - just as in a conventional gasoline engine - as incoming air
rushes down the air inlet tube, it will pick up alcohol vapor metered
through the carburetor ... which should have a controllable throttle to
match tractor load.
Another way to use ethanol in a diesel engine is to install fuel
injectors into the intake manifold to accomplish the same result. This
system would require a separate pump that would have to be timed in
order to inject alcohol at the proper moment.
A vaporizer - like those found on propane fuel systems - can also be
used to add alcohol to the diesel fuel system. This, again, provides the
diesel intake manifold with ethanol vapors that help combustion.
Since a diesel engine has closer tolerances and is more costly to repair
than a conventional gasoline engine, you should take extreme care when
altering and running diesel equipment on other than pure diesel fuel. If
you don't consider yourself competent to work on diesels, find someone
who is ... since the diesel fuel injector pump must be adjusted to
provide less flow when alcohol fuel is used, plus the fact that a lean
mixture condition - and even increased horsepower outputs - can damage a
diesel engine in short order.
Turbocharged diesels can be equipped with what is known as an "aquahol"
injection system, to be marketed by the M & W Gear Company of Gibson
City, Illinois early in 1980. This setup injects a fine mist of alcohol
and water in a 50/50 ratio directly into the engine's air intake, which
results in a lowering of fuel consumption and a tolerable increase in
DURABILITY OF VARIOUS PLASTICS: ALCOHOLS VS. GASOLINE
Excellent: Will tolerate years of exposure.
Fair: Some signs of deterioration after one week of exposure.
Good: No damage after 30 days of exposure, should tolerate several years
Poor: Deteriorates readily.
NOTE: All tests were made with liquids at 122 deg F.
Earth Alcohol Fuel
Introduction to a Farmer's
Fuel ... Alcohol
Introductory Overview of the Alcohol Production Flow Chart
A Short But Complex Story About Enzymes and Their Functions
Farm Crops for Alcohol Fuel
More on Raw Materials
Feedstock Handling and Storage
Basic Steps in the Production
of Ethyl Alcohol
More On Conversion and Fermentation
Control of Infection by Planned Sanitation in the Production of
Fuel or Gasohol Alcohol
MOTHER's Mash Recipes for
Important! Read Before Making Mash
Preparing a Mash From Saccharide-rich Materials
A Handy Hydrometer Jacket
Animal Feed By-product
More Information On By-product Utilization
How the Distillation Process
Bubble Cap Plate
The Reasoning Behind MOTHER's Still Design
Making Your First "Run"
"Economizing" Your Alcohol Production
Six-Inch Column Still Plans
Three-Inch Column Still Plans
Bill of Materials
Two Low-cost Backyard Stills
Alcohol as an Engine
How To Adapt Your
Automobile Engine For Ethyl Alcohol Use
Do-It-Yourself Water Injection System
MOTHER's Waste Oil Heater
Biofuels supplies and suppliers
Make your own biodiesel
Mike Pelly's recipe
Two-stage biodiesel process
FOOLPROOF biodiesel process
Biodiesel in Hong Kong
Nitrogen Oxide emissions
Biodiesel resources on the Web
Do diesels have a future?
Vegetable oil yields and characteristics
Biodiesel and your vehicle
Food or fuel?
Straight vegetable oil as diesel fuel
Ethanol resources on the Web
Is ethanol energy-efficient?