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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

Mechanical Or Electric?That raises the next question. Should you use a mechanical pump or an electric one? This is a money issue first and a car-design issue second. If you are making the kind of power we are, the mechanical pump is the less expensive option. The pump mentioned earlier retails for $85.95 and, according to the math, can feed right around 500 hp. The inlet and outlet are also tapped for 31/48-inch line, so you can use your stock fuel system (unless your car is equipped with 51/416-inch stuff; then you should upgrade that anyway). There are mechanical pumps out there that will pump up to 225 gph and feed 675 hp, but you will need to buy a regulator and some AN fittings and lines, so be sure to factor those into the total cost.

There is also driver preference. Circle track guys like it when the mechanical fuel pump quits when the engine dies so that if they flip the car, the pump isn't glugging fuel all over the hot parts while they are headfirst in the clay. Street machine guys usually like to hear that pump whirring away and see the filter or the pump itself mounted next to the fuel cell. It's cool. Drag racers like to know that when the engine is on, the fuel pump is at maximum pressure and ready to go on a hard launch. Electric-pumps start at maximum pressure and flow, and flow drops as pressure increases. Mechanical pumps start at low flow and increase with rpm. Because of that, the mechanical pump uses and delivers fuel based on demand.

In our case we are going to be pumping up the horsepower to 550 or so, feeding a tunnel-ram, and eventually running a parallel nitrous system. The stock fuel tank hits the differential and leaks, so we are going to either install a fuel cell or get a replacement tank and add a sump. All of this leads us to a trunk-mounted electric pump for easy access and track maintenance. We also like the mechanical noise and the glamor.

Return or dead head?The term "dead head" simply means that the fuel in the system does not recirculate back to the gas tank from the front of the car. A return system recycles fuel back to the tank using either a bypass at the fuel pump or at the regulator.

Engines with mechanical pumps can use dead-head systems because fuel pressure only increases with rpm and the design of the pump only allows as much fuel into the pressure side of the system as is needed by the carburetor. Although there are some factory musclecar-era machines that use a return system, most do not for this reason. We ran a mechanical pump with no return line for two years and, even though we drove it to Vegas in scorching heat, never had a fuel-related problem.

When you add an electric pump to a dead-head system, fuel is constantly working against the pressure regulator or being bypassed within the fuel pump itself, causing extra heat and sometimes air to be forced into the system. The more of each you add, the closer you get to the point where the fuel becomes so hot that it turns to vapor and stops being delivered to the engine. On a car that sees the street and long road trips, the result is trouble. This situation also causes a pressure drop, as the needle and seat open to fill the bowls of the carburetor, and constant starting and stopping of fuel flow. These problems are why factory fuel-injected cars with electric pumps always use a return system.

A typical Barry Grant (BG) return system works by pumping fuel pressure to the regulator mounted downstream of the carb. Since the regulator will be set to provide 6-8 psi, the unused fuel will be sent back to the gas tank or fuel cell. This ensures that the fuel is constantly flowing and that fresh, cool fuel is always available at the carburetor. Another advantage to the return system is that the fuel pressure is the same throughout the system, eliminating pressure drops between the regulator and the carbs and ensuring that fuel-pressure settings remain constant under load.

By Barry Grant Fuel Systems
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