Weldon Fuel Pump - Let It Flow

Taking The Mystery Out Of EFI Pumps

Bob Mehlhoff Jan 19, 2007 0 Comment(s)

Keep it Regulated
Unlike a typical carburetor regulator, which controls pressure between the regulator and the carburetor, on an EFI system a bypass regulator controls pressure between the bypass regulator and the pump. This means the bypass regulator should be placed after the fuel rail(s) whenever possible. If your system is a dual-rail, be sure to employ a Y-block to split the supply line before entering the rails and run individual lines from the opposite end of each rail to each inlet port on the regulator. A setup like this serves to provide constant fuel pressure and flow volume through the fuel rail and to the injector inlet.

Sump Your Tank or Go Cellular
If you'll be making no more than 500 horses, chances are your stock tank may work well if the rest of your fuel system is properly designed and maintained. Keeping your stock tank allows you to have a larger capacity than most fuel cells, a standardized mounting position, an easy-to-reach cap, and a well thought-out ventilation system.

If you plan to make over 500 horses, though, there are several reasons you should consider installing a correctly engineered sump and the appropriate fittings or completely replacing your tank with a racing fuel cell. Remember, a stock pick-up assembly-even when used with a high-performancein-tank pump-may become too restrictive for high-horse-power applications. Some builders remedy this situation by replacing the in-tank fuel pump/pickup assembly with a larger fabricated unit, which feeds an externally mounted, high-flow fuel pump.If this is done be sure to keep the tank more than half full during hard driving. Common problems associated with using fabricated pick-up assemblies in stock (unmodified) fuel tanks are pump cavitation, vapor lock, varying fuel pressure, exaggerated pump wear, and lean conditions during both low and high loads. Additionally, many stock tanks do not have the proper internal baffling or fittings to correctly install adequately sized return lines.

With a good sump correctly installed into a stock tank, the restriction of fuel flow through the sump box and to the actual pick-up point is drastically reduced. Thisis because a sump offers a much larger reservoir that holds enough fuel to support lots of power (with some sumps over 1,000 hp) at wide open throttle and ongoing inertia forces in many directions. This can be accomplished while holding fuel at the pickup during cornering and braking maneuvers, with as little as a quarter of a tank.

Fit to Flow
Fuel lines should have an easy-to-follow, unrestricted path on both the feed line and the return line. Depending on the application, you'll want to use at least AN-8 line (11/42-inch id), and for engines with more power than 600 horses consider AN-10. When making your feed and return line remember the return line should be no smaller than the feed line, so the bypassed fuel has an easy return to the tank. All feed and return lines should have smooth paths without hard 90-degree turns.

At low speed the regulator and return line combined must flow almost all of the fuel pump's volume. If not, the resulting fuel pressure is considered a false-high. This means pressure is out of the regulator's control and will drop to the actual regulator set point as the engine goes under load (WOT). A good test for correct regulator and return-line selection and performance is to check if the pressure will adjust at least 5 psi below the desired base pressure, with the vacuum line disconnected.

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