Richard Holdener
October 1, 2012

Upgrading Your System

Upgrading the fuel system on nearly any Mustang (from '86-present) is pretty straightforward. For early (return-style) applications, the installation of a 255-lph fuel pump will provide sufficient fuel flow for nearly 650-800 horsepower, assuming a system pressure of 40 psi, a supply voltage of at least 12 volts, and 0.5-brake-specific fuel consumption (BSFC).

Actually, testing has shown that most normally aspirated fuel-injected 5.0L and 4.6L applications exceed a 0.5 BSFC number and often dip down into the mid-0.4s. This means that the engine 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. Even a dedicated (normally aspirated) race motor could get by with a 255-lph, or certainly an Aeromotive Stealth in-tank pump (assuming proper wiring and fuse capacity).

Most normally aspirated engine can get by with 40 psi, but the same doesn't hold true for forced-induction applications unless overly large injectors are employed. Judging by the flow numbers in our pump test, combining a 255-lph in-tank pump with a Kenne Bell Boost-A-Pump should handle just about any 5.0L or 4.6L combination you are likely to throw at it, including high- horsepower, turbo, or blower engines.

Upgrading to a Stealth Pump from Aeromotive or TI pump from Walboro with the Boost-A-Pump will provide more fuel than you could even use. There are some minor exceptions to this rule, like the '11-up Four-Valve Coyote motor. Since the fuel system is self-regulated at just 55 psi (at the pump), a high-flow pump must be combined with large injectors if you plan to exceed 850 rwhp. The '03-'04 Cobra and Shelby GT500 both utilized dual pumps from the factory, so pump replacement requires a pair of pumps. Adding a Kenne Bell Boost-A-Pump to the stock pumps will take you beyond 800 hp with the right size injectors, making pump replacement unnecessary for all but dedicated race motors. Shelby currently employs the Boost-A-Pump on its Super Snake GT500 vehicles.

The Walbro GSS340 was the typical 255-plh pump employed on a variety of different Mustang and other applications. The Walbro TI F262 was a new in-tank pump designed for gas, while the TI F267 in-tank pump was the only one tested specifically designed for use with alcohol-based fuels. The Stealth from Aeromotive and Walbro TI pumps were high-flow in-tank pumps that easily out-performed the venerable 255, while the A1000 (offered in both inline and in-tank configurations) offered the most flow of any of the pumps tested. On some applications, the A1000 required the entire fuel system be upgraded with new plumbing, regulator, and wiring. Due to the extreme flow rates, the F262 and F267 TI pumps would require attention to the wiring and fuse components, as would other after-market/non-OEM pumps in dual (or triple) configurations.

Photo Gallery

View Photo Gallery

Common Injector Flow Rates vs. Power Output High-Impedance Injector Flow Ratings


Max HP

Injector(0.5 BSFC)(0.6 BSFC)
19 lb/hr304 hp253 hp
24 lb/hr384 hp320 hp
30 lb/hr480 hp400 hp
36 lb/hr576 hp480 hp
40 lb/hr640 hp533 hp
42 lb/hr672 hp560 hp
50 lb/hr800 hp667 hp
55 lb/hr880 hp733hp
65 lb/hr1,040 hp867 hp
75 lb/hr1,200 hp1,000 hp
85 lb/hr1,360 hp1,133 hp