AEM 30-6905 Universal Programmable EMS-4 - Manual (Page 135)

Page 135 of 279 EMS-4 Install and Tuning Guide_Rev 1.6
Double click the Output Function column next to the chosen GPIO pin. Select Fuel Pump.
Activate the Enable Pin checkbox. Be sure the Switch Input is set to Ignore Switch Input. Pin
conditions must be set such that they are met all the time. Define the required Fuel Pump
Prime setting. At key on, the fuel pump output will activate for this amount of time then shut off
if no engine RPM signal is detected.
Fuel Pump Sizing
To achieve proper fuel delivery, you must select the right fuel pump for your vehicle. In most
cases, where the engine has been modified only with “bolt on” performance items, there is
rarely need for a larger fuel pump or larger injectors. Vehicle manufacturers typically design a
“safety factor” into the fuel pump to accommodate the deterioration of the fuel system over time.
This safety factor is intended to compensate for a fuel filter that is nearing the end its life, or for
deposits in the injector orifice. Our research has revealed that generally there is about a 15%-
20% oversize in most factory fuel pumps.
If the engine is enhanced via forced induction or nitrous oxide, the stock fuel pump is
inadequate.
If the engine’s power is increased more than 15-20% fuel delivery must
increase as a factor of the power gain.
The way to determine the proper-size fuel pump is based on the desired brake specific fuel
consumption (BSFC) of the engine. This term refers to how much fuel in pounds per hour (pph)
the engine consumes per horsepower and is a measure of the efficiency of the engine. It is a
useful term in determining the total fuel requirement of the engine.
On vehicles equipped with forced induction or nitrous oxide, higher BSFC‟s are required as an
added measure of safety to prevent detonation or high combustion chamber temperatures.
Below is a guide of BSFC‟s with standard CR that AEM uses for various engines that run on
gasoline:

Naturally Aspirated engines have a BSFC of .48 to .50

Forced Induction engines have a BSFC of .65 to .68
Methanol (alcohol) powered engines require twice the amount of fuel so the BSFC‟s are
doubled.
Calculating the total fuel requirement of an engine requires simple equations that we outline in
the following section. You must know how much power the engine is anticipated to make and
we recommend that you guess on the high end. The fuel requirement will be determined in
pounds per hour of fuel flow. Since most pumps are rated in gallons/hour you must know the
weight of your fuel/gallon. (The vast majority of gasoline based fuels run at 7.25 lbs./gallon.)
The equations to determine your fuel requirement is as follows: