Fuel Pump Technology Inside Ford Mustang

The problem with this type of rising-rate fuel management system (FMU) is that it made life much harder on the fuel pump. Not only were we asking the fuel pump to support the additional power potential of the force-fed Ford, but also to do so at a greatly increased fuel pressure. Not surprisingly, many early attempts met with less-than-stellar results as the stock fuel pumps simply refused to cooperate under such adverse conditions. The cure to the problem was to increase the flow potential of the fuel pump.

Many approaches were taken to improve fuel flow. Naturally it was possible to simply install a better-flowing fuel pump in place of the stock 88 lt-hr pump. The aftermarket supplied fuel pump upgrades ranging from 110 lph all the way to a whopping 255 lph. It was also possible to install an inline fuel pump to work in conjunction with the stock (or upgraded) in-the-tank pump. The benefit of the inline pump is that it can be installed without dropping the gas tank.

Additionally, the high-flow inline fuel pump helps improve the fuel flow of the feed pump (stock or otherwise) by reducing the system pressure between the two pumps. Since the inline pump outflows the in-the-tank pump, the pressure between the two pumps decreases. The reduced pressure helps increase the flow potential of the feed pump, thus improving the overall system. It is important to note that the limiting factor of the inline system will still be the pump with the lowest flow rate. If the stock 88 lph fuel pump increases to 150 lph at 0 psi and your inline pump flows 200 lph, the maximum system flow will still be limited to 150 lph.

Another popular method made popular by Kenne Bell is to increase the supply voltage to the fuel pump. The K-B Boost-a-Pump improves the flow rate of an electric fuel pump by increasing the supply voltage. Most fuel pumps are (flow) rated at 12-13 volts. If you have a fuel pump rated at 255 lph at 13 volts, know that the flow rate will dramatically increase if the voltage supply is increased from 13 to 17 or even 20 volts.

Check out the supplied charts to illustrate the increase in flow rate offered by the Kenne Bell Boost-a-Pump. All of our fuel pumps were flow tested at 13 volts and then again at 17 volts. The increase in flow rate was impressive, especially when you consider that the installation of a Boost-a-Pump is much easier than even an inline pump. Hooking up the Boost-a-Pump is a simple matter of connecting two power wires and a single ground. The Kenne Bell unit can even be dialed in to produce the desired voltage and activated under boost or 0 vacuum (wide-open throttle).

Internet rumors that the increased voltage will somehow diminish the life of the fuel pump are unfounded. Ease of installation, the ability to control onset and supplied voltage, and to increase the flow rate of nearly any electric fuel pump by 30-50 percent makes the Boost-a-Pump an attractive option.

For the 5.0 and early 4.6 applications that feature the return-style fuel system, the installation of a 255-lph fuel pump will provide sufficient fuel flow for nearly 800 hp--assuming a .5 brake specific fuel consumption (BSFC). Actually, testing has shown that most normally aspirated fuel-injected 5.0s and 4.6s applications exceed a .5 BSFC number and often dip down into the mid .4s. This means that the motor will require less fuel to produce a given amount of power.

While your first thought might be that this entails a lean mixture, it is possible to increase the power output without affecting the air/fuel ratio, thus improving (decreasing) the BSFC number. Producing 800-plus hp with a 255-lph fuel pump also assumes a fuel pressure of 40 psi. While most normally aspirated motors can get by with 40 psi , the same doesn't hold true for forced-induction applications unless overly large injectors are employed. Combining a 255-lph in-tank pump with a Kenne Bell Boost-a-Pump should handle just about any normally aspirated combination you are likely to throw at it. This of course assumes you have large enough injectors, adequate-size wiring to the fuel pump, and a good fuel system including fuel filter and rails.

While a simple 255-lph fuel pump combined with a Kenne Bell Boost-a-Pump might take care of most normally aspirated (return-style) combinations, the same does not hold true for turbo or supercharged combinations. For all but low-boost, bolt-on applications, the rising-rate fuel-management units that increase fuel pressure in (somewhat) relation to boost should be avoided. The key to a successful supercharged or turbocharged motor is in the tuning. A major portion of the tuning is the fuel system, namely the injectors and fuel pump (combined with the proper dyno-tuned computer chip).

The reason that the fuel pumps will not support as much power on forced-induction applications is that the fuel pressure will always increase at a (minimum) 1:1 rate with boost pressure. This means that if you run 10 psi of boost, the fuel pressure that started out at 40 psi will now be 50 psi, as the fuel-pressure regulator on all return-style fuel systems are vacuum/boost referenced. This is done to decrease fuel pressure under vacuum (low fuel demand) conditions to help lean the mixture. As mentioned earlier, the flow rate of the fuel pump will decrease with the increase in pressure, thus the pump will be able to support less absolute power at 50 psi than it could at 40 psi. It should also be pointed out that though the injectors see 50 psi of fuel pressure, it must flow against 10 psi of boost pressure, thus giving the injector the delta flow of only 40 psi.

This same scenario occurs on the later returnless fuel systems due to the pressure transducer in the fuel rail. When running a blower or turbo on a 4.6 equipped with a returnless fuel system, boost pressure will be applied to the diaphragm of the pressure transducer, thus making the computer increase fuel pressure to compensate to produce the original desired pressure.

If the computer called out for 40 psi of fuel pressure under a given situation, but the supercharger (or turbo) was producing 10 psi of boost, the computer would continue to provide pulse width modulation (voltage) to the fuel pump until a delta pressure of 40 psi was achieved. This would require the computer to raise the actual fuel pressure to 50 psi to compensate for the additional 10 psi of boost.

This same scenario takes place on the supercharged '03-up Cobra, especially as owners increase the boost pressure by installing larger crank or smaller blower pulleys. We have seen fuel pressure as high as 80 psi on modified '03-04 Cobras equipped with twin-screw blower upgrades. The fuel pump(s) on these Cobras flow well, but the fuel flow decreases dramatically when jumping from 40 psi to 80 psi.