by Phil Ross aka. HoosierBuddy
"Pumps don't suck," Professor Davis liked to tell
our Hydraulic Power class. "Or, at least they don't like
to" he would sometimes add.
The concept that
pumps don't suck might come as big news to anyone with a car
like the beauty on Fast Phil's sign; a 1965 Mustang that was
equipped from the factory with a mechanical fuel pump. Located
several feet away from the car's
stock 16 gallon
fuel tank, this pump was designed to suck gasoline through
a 5/16" fuel line, pressurize that fuel to around 5 pounds
per square inch, and pump it into the carburetor's fuel bowls
for later delivery to the engine. While a mechanical diaphragm
pump is designed to suck gasoline, Professor Davis' point
is still somewhat true. Even though they will if they have
to, pumps don't like to suck. Pumps work much more efficiently
when they have a "pressure head." Fuel pumps are
happiest when they are being fed a steady of diet clear, cool
pressurized gasoline. This positive feed is one of the major
advantages a tank-mounted, or in-tank fuel pump has over an
old style engine-mounted pump. If properly designed, these
newer style systems use gravity to feed fuel into the inlet
side of the pump. A pump that is being fed fuel has a much
easier job than a pump that has to suck fuel.
|Phil Ross is a FordMuscle
contributor and goes by the handle "HoosierBuddy"
on the FM Forums. He drives a 1965 Mustang Convertible
which is in the process of receving a fuel injected
Another major disadvantage of pulling fuel from the tank all
the way to the front of the car is that volatile gasoline
exposed to the pump's vacuum and heat can tend to vaporize
in the fuel line. Vapor lock, the bane of many high performance
cars, can easily occur when this happens. A fuel pump that
struggles to suck liquid fuel from the tank will fall flat
on its face if it suddenly loses prime when low pressure fuel
turns from a liquid to a gas while still in the fuel line.
This can cause the pump to run dry and wear out in a very
So, what's the horsepower loving street driver to do when
the old stock mechanical pump just won't bring it anymore?
Turn to a high performance mechanical pump? A pump that will
create even more vacuum and heat than a stock pump? For a
street driven car in the summer, that fix can be like using
gasoline to put out a fire. A high performance mechanical
pump may work great on a strip car that gets run hard and
shut down quickly, but on the street, that expensive race
pump can cause some serious headaches.
A better solution is to ditch the stock mechanical fuel pump
mounted on engine's front cover, and go with a pump mounted
closer to the gas tank. Your grandfather might have seen a
few vacuum driven pumps before the war, but in this day-and-age
a pump mounted away from the engine is generally powered by
electricity. A good electric fuel pump, properly sized, selected,
and installed can be a great improvement for your hot rod
or vintage muscle car.
Keep in mind though that electric fuel pumps are not all the
same. Pumps are rated to operate at different pressures and
different flow rates. Also, while many electric fuel pumps
are designed to be mounted between the gas tank and the engine,
some are designed to be mounted inside the tank itself. While
mixing the electricity that it takes to run the pump with
gasoline might seem a bit disingenuous at first, in fact that
is the system that is preferred in many OEM applications like
all late model mustangs. Newer mustangs and many other late
model cars have their fuel pumps mounted in the gas tank.
In-Tank Fuel Pump Considerations
When considering a retrofit installation, mounting the pump
in the gas tank is a little more involved than mounting it
outside the tank. Mounting the pump in the tank has a few
definite advantages though. Most importantly, the fuel tank
inlet can be located very close to the lowest point on the
inside of the tank with relative ease. Secondly, the pump
itself is submerged in gasoline that will keep it nice and
cool when it's in operation. Third, a pump that's inside the
gas tank tends to be quieter than a pump mounted in the open
in front of the gas tank. Finally, locating the pump in the
tank eliminates the hassle of trying to find the perfect compromise
location for an externally mounted pump. External pumps work
better the lower they are mounted. However, get them too low
and they might get hit by something off the road. Once you've
decided to mount the pump in the tank, you have all the room
in the world, or at least all the room in the tank, to mount
While mounting a pump in a late-model mustang gas tank that
was designed for that specific purpose is a fairly simple job,
mounting a pump in an older tank that has no provision for an
internal pump has involved a lot of engineering, custom design
and fabrication for those hardy souls that have pioneered in-tank
fuel pump mounting for older cars. Luckily, as more and more
hot rods and muscle cars have been converted to Electronic Fuel
Injection, that by its nature requires higher fuel pressure,
necessitating electric fuel pumps, the aftermarket has responded.
Tanks Incorporated manufacturers
and sells complete "universal" in-tank fuel pump assemblies
that can serve as the basis for an in-tank electric fuel pump
system. The Tanks Inc. unit is a well thought out assembly that
already has the engineering and design work built right in.
This is good news for those of us that are ready to upgrade
our fuel systems for the new millennium.
Although it is possible
to assemble the PA-4 kit into an existing gas tank, this does
create a large safety concern. It is extremely difficult to
empty a gas tank completely, remove every bit of gasoline residue,
and vent all the flammable vapors left by gasoline. Never cut,
drill, bore, weld or file on a gas tank that has the slightest
trace of gasoline in it. The safest and best thing to do is
to purchase a new fuel tank for this sort of conversion.
For our installation on a 1965 Mustang Convertible, we
elected to ditch the old, original style 16-gallon tank
and install a 20 gallon tank that was designed for a 1969
Mustang. This tank is the same width and length as the
stock unit, but is slightly taller above the flange to
allow for the additional capacity.
The unit shown is an American Designers tank manufactured
north of the border by our friends in Canada. It includes
a very handy drain plug too. Be aware the sending unit,
which powers the car's fuel gauge, must be matched to
the gas tank. So in this case, we needed to purchase a
new sending unit for a 1969 mustang as well. It will work
fine with the stock gas gauge.
The pump assembly should be mounted toward the front and
near one side of the tank to maximize the benefit of the
anti-slosh baffling. Here, the 6" diameter mounting
ring is used as a template to draw an outline of the hole
that must be made in the tank. A jigsaw could be used
to make this cut, but if available, a hole saw will make
short work of this job.
Since we planned to use a hole saw, the next step was
locating the exact center for the pilot hole. If you remember
anything from high school geometry, you might remember
this: 2 chords struck across the intersections of two
radii scribed from the circumference of a circle will
cross at the circle's exact center.
have your smart teenager show you how
to find the center of a circle or make your best guess
and start drilling. Either way, you'll end up with a hole.
After center punching the exact center for our circle,
we proceeded to void the warrantee on our new American
Designer's 20-gallon tank. A 4 ½" hole saw
is the slick way to make this cut. Unfortunately, a lot
of hardware stores don't carry hole saws bigger than 4"
and the ones that do charge about 35 bucks for one. Luckily,
a friend of a friend was found that had this saw in their
tool box and made it available. Aren't friends with tools
great to have around?