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Fuel System - How To

This story has all the math and goodies for your next fuel-pump install so you'll do it once and get it right.

By Barry Grant Fuel Systems, Photography by

If you are stubborn and want a dead-head-style system or are clicking off 1.20 60-foot times in a trailered race car, BG offers the BG400 pump, which has an externally adjustable bypass right at the pump that can return fuel to a rear-mounted fuel cell or tank. It's really not designed for street use, but for burger-stand guys and short trips, there is a power stepdown box that will cut the voltage to the pump so it will not overheat. A toggle switch is used to put it into street driving mode, then a throttle switch takes the system back to full voltage at WOT. Pretty neat.

If you still insist on trying a dead-head system, there is the Enduro series from BG, which allows you to run a big electric pump on the street. The trick is an internal bypass and a fuel-cooled gerotor-style motor. The King, Mighty, and Speed Enduro pumps can feed 2,000-, 750-, and 500hp engines respectively and can also be hooked to an additional aluminum heat sink if necessary for additional abuse.

RegulatorsAt the very low end of the fuel pump spectrum you can find fuel pumps that don't require a pressure regulator of any kind. They are the mechanical pumps that provide less than 110 gph free flow and don't build pressure much higher than about 8 psi, and electric pumps that provide less than 100 gph free flow and don't build pressure above 7 psi. If you need more pump, you need a regulator.

Using Holley carburetors as an example, the needle-and-seat assembly can control fuel flow up to about 8 psi. Any more than that and unregulated fuel will flood the bowl, enter the carb through the venturi as it pours out of the vent tubes, and stall the car at idle or create a huge rich condition at full throttle. The regulator simply uses spring pressure to regulate fuel pressure. There is a screw or Allen bolt on top of the regulator that when turned clockwise adds preload to the spring, increasing the amount of pressure required to unseat the regulator. A dead-head-style regulator simply stops fuel from flowing when the valve is closed. A return-style regulator allows fuel to flow back into the tank. There are several sizes available, but the basic breakdown is for either 31/48-inch or 11/42-inch fuel line. There are also four-port regulator dead heads for tunnel-rams and single-return styles for multiple carbureted street machines.

When using return-style regulators, it's important that the return line is within one size of the feed line. If the line is too small, fuel will not be able to return to the tank fast enough and you will not be able to lower the fuel pressure at the feed line no matter how many times you turn the screw.

Since every pressure regulator has fuel pressure versus spring pressure vented to atmosphere, you can run a fitting to manifold pressure. On boost, the extra atmosphere will increase fuel pressure at a 1:1 ratio. Nitrous guys should have a separate fuel system for safety reasons. If the main fuel system fails at full throttle, the nitrous will still be spraying. With a separate line you can run a safety switch that kills the nitrous when fuel pressure drops below a predetermined limit.

Fuel LinesWe've been having a small debate about the size of the feed line from the fuel tank or cell. BG recommends a -12 (31/44-inch) line for the BG-400 and even sent us a photo of a cavitated pump as proof that bigger is better. The theory is that since electric pumps are designed to push and not pull, they need all the help they can get. Yet most fuel cells come with a -8 (11/42-inch) line, and the guys at Holley saw no problem with a -8 feed. What BG and Holley agree on is that the primary line should be -8 (11/42 inch) from the pump to the regulator and at least -6 (31/48 inch) on the way back.

By Barry Grant Fuel Systems
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