Fuel Pumps and Regulators
Typically, at wide open throttle, full power, an engine requires 0.5 lbs. of fuel
per horsepower every hour. A gallon of gasoline weighs approximately 6 lbs.
Therefore an engine rated at 350 horsepower will require about 175 pounds
(29 gallons) of fuel every hour.
(350HP x .5 lbs = 175 lbs of fuel
175 lbs/6 lbs = 29 gallons per hour)
FUEL PRESSURE AND VOLUME
The relationship of pressure to volume is inversely proportional. That is, as
pressure increases the volume will decrease, everything else being equal. A
certain amount of fuel pressure is always required to maintain engine performance
by assuring that fuel is available on demand. Also, other factors
and conditions must be taken into account such as acceleration G-forces and
friction within the fuel system itself. At the same time,however, an adequate
fuel volume is needed to ensure that the proper amount of fuel can always
flow to the engine, especially during peak demand situations. A basic understanding
of this critical pressure/volume relationship is needed when designing
the proper fuel supply system for your vehicle.
FUEL LINE SYSTEM
The fuel line system should be routed to avoid running near hot spots, such as
various exhaust system components, and designed to promote maximum fuel
flow. Most factory stock fuel systems utilize 5/16" fuel lines. This size works
well on street applications with stock engines. When the horsepower requirements
go up, however, the inadequacy of this line size soon becomes apparent.
A #6 (3/8") line size is sufficient for all street performance applications
and some racing applications. #8 (1/2") fuel lines are used on everything
else, including alcohol applications. Avoid using rubber fuel lines, or use
them sparingly, for two reasons. First, rubber is more resistant to the flow of
fuel than any hard line. An actual pressure loss can be measured over distance.
Second, for safety’s sake, it’s not a good idea to use rubber fuel line,
especially when using a high pressure performance fuel pump.
FUEL LINE FITTINGS
Like the fuel line, fuel line fittings are also a very important element in the total
fuel line system and should not be overlooked. Obviously, the fittings should
be the same size as the fuel line. Also, if at all possible, you want to minimize
the use of 90° fittings. Avoid sharp turns or bends in the fuel line routing;
these cause undue restrictions to the flow of fuel.
Various Holley mechanical fuel pumps are available. 110 GPH pumps are
designed for street/strip applications where substantially higher than stock fuel
delivery requirements are necessary. 3/8" inlet and outlet ports are utilized
and, with fuel shut-off pressure in the area of 6-1/2 - 8 PSI, a regulator is
not required. 130+ GPH pumps are available when maximum fuel delivery is
desirable. 1/2" inlet and outlet ports are included and fuel shut-off pressure is
between 7-1/2 - 9 PSI. A pressure regulator is definitely required. Both the
110 GPH and 130+ GPH pumps utilize a high capacity fuel valve design that
will ensure an adequate fuel supply is always available.
Holley offers a complete line of electric in-tank and externally-mounted pumps.
Holley externally-mounted electric fuel pumps are also available in various flow
ratings. The “red” pump, P/N 12-801-1, is rated at 97 GPH and it is designed
to work with stock or mildly modified engines. Pressure is pre-set to 7 PSI and
a regulator is not required. The “blue” pump, P/N12-802-1, is rated at 110
GPH and it is designed for street/strip applications. Pressure is pre-set at 14 PSI
and a regulator is included as part of the package. Neither pump is compatible
with methanol or alcohol fuels nor should they be used with fuel injection systems.
The “black” pump, P/N 12-815-1, is rated at 140 GPH and is designed
to work with either gas or alcohol fuels. This one is similar to the “blue” pump
but it kicks out more fuel. These pumps all feature a simple, yet rugged, rotor
and vane design which has proved itself over the years.
Two very powerful “VOLUMAX” pumps are available for gasoline or alcohol
fuels. They are P/N 12-705-1, rated at 180 GPH and P/N 12-706-1, rated at
275 GPH. These feature a gerotor pump design which is extremely efficient
and quiet. Fuel pressure is pre-set at 15 PSI and both a pressure regulator and
3/8" return line to the tank are required. The high volume output of these
pumps make them the natural choice for racers who will settle for nothing but
the best. NOTE: Because of the design of these pumps, it is necessary to connect
both fuel pump inlets to the fuel supply for proper operation.
Our electric in-tank line overs coverage for the most popular Ford, Chrysler,
GM and Import applications. Utilizing a proven gerotor design, these pumps
are available in either a 190 or 255 liter per hour (lph) flow rate.
OIL PRESSURE SAFETY SWITCH
It’s always a good idea to place a safety switch in the circuit when installing
an electric fuel pump. Holley has one available under P/N 12-810. This
switch will ensure that the electric pump will not work unless the engine has
oil pressure. It will prevent the pump from running in a situation where the
motor may stall with the ignition ON. Wiring the switch through the starter
solenoid circuit energizes the pump on engine start-up. After the engine is
running the switch continues to provide power to the pump as long as there is
oil pressure to keep the switch turned on.
FUEL PRESSURE GAUGES
There are a number of places where mechanical fuel pressure gauges could
be effectively mounted. One place is just before the carburetor. Holley
chrome dual feed fuel lines (except model 4500 DOMINATOR) and fuel blocks
all have a tapped 1/8 NPT provision for this purpose. Another would be at
the outlet side of the pressure regulator. The Holley four-port Pro-Series
VOLUMAX regulator incorporates two pressure gauge taps expressly for this
purpose. The electric fuel pressure gauge can be mounted inside the vehicle
so that fuel pressure can be monitored while driving. This is possible because,
unlike the mechanical gauges, fuel does not flow up to the gauge itself. The
Holley electric gauge, P/N 26-503,utilizes a remote sending unit which is the
primary fuel pressure sensor.
Holley offers a variety of fuel pressure gauges, depending on use. For carbureted
vehicles there are two (2) mechanical and one (1) electric gauge available
in the 0-15 PSI range.
Vehicles equipped with low pressure (up to 30 PSI) fuel injection systems (like
throttle body fuel injection systems) can choose from two mechanical pressure
gauges in the 0-30 PSI range.