How much fuel flow is enough?
The correct volume of fuel is that which is required to support the amount of horsepower that the engine can produce. Most engines that are using gasoline burn approximately .5 pounds per horsepower-hour. This is sometimes called BSFC (Brake Specific Fuel Consumption). What this means is that for each horsepower produced, it takes ½ pound of fuel. This is a general statement and sometimes engines can be a little more efficient than .5lb/hp-hr., but it is a good practice to plan and measure fuel system operation using this number. Carburetors must have a stable supply of fuel in order to maintain the correct liquid fuel height. This is most difficult with drag racing vehicles that sometimes have forward acceleration and wheel stand at the same time. Each time that a nitrous system is engaged, additional fuel supply demands must be met or melted parts may result from "system lean-out." The fuel required is in excess of the .5 lb/hp-hr. for normally aspirated conditions. The additional fuel requirements for nitrous system planning is about .7 lb/hp-hr.
How much fuel pressure is necessary?
First, the fuel system pressure (provided by the fuel pump) must be enough to oppose the effects of gravity during the launch and during the run for drag racers. The system pressure of at least 8 to 10 psi per g is generally adequate. MagnaFuel ProStar 500 Series pumps are factory set to 28 to 30 psi. They are field adjustable from 24 to 36 psi. The MagnaFuel QuickStar 300 Series pumps are factory set to 25 psi and field adjustable from 25 to 36 psi. The QuickStar 275 series pumps are factory preset to 18 psi (these units are not field adjustable). MagnaFuel regulators need to be adjusted to 6.5 to 7.5 psi WITH FUEL FLOWING at a rate of about ½ cc per second (that's about 10 drops per second). Higher fuel pressure will generate more foam in the float bowl.
How can you plan your racing fuel system?
Use a handheld calculator and plan on .5 lbs/hp-hr. (gasoline). Methanol alcohol requires about 1.0 lbs/hp-hr. Use .7 lbs/hp-hr when planning a gasoline system for nitrous assist. EXAMPLE: You have a 650 hp engine. 650hp x .5 = 325 lbs/hr. (gasoline). Although you need to know how much your fuel weighs, assume for this example that it weighs 6.2 lbs/gal. 325 lbs/hr. ÷ 6.2 = 52.42 gal/hr. Dividing by 60 (minutes per hour) yields .847 gal/min (GPM). Check the graph and specification information for a pump selection for your application. Note that this flow number is what your engine needs at the float bowls. So you also need to check out the graphs and specs for a MagnaFuel regulator.
Should you use a fuel filter?
All fuel systems are dirty and need to use a filter in the system. The filter should be located on the suction side (between tank and pump) of the pump. The filter cartridge is washable. Replacements are available.
Why do you need a high-output, high-pressure fuel system?
Todays race cars need more fuel system than ever before because of improvements in torque, RPM and horsepower. As carburetors, manifolds and cylinder heads improved in airflow capacity, the need for more efficient racing fuel systems grew substantially. More efficient chassis and tires created the need for more fuel in order to maintain the maximum output power of the engine. Simply put, the harder the race car launches, the higher the system pressure must be to overcome the effects of gravity that cause restriction to flow. Firemen plan for this restriction to flow by adding 5 psi to the fire hose pressure per floor above street level. Pilots flying in high-performance fighters must control their blood supply with exercises and special flight suits when in high g-factor maneuvers or they suffer “redouts” or “blackouts” because they can't control their blood pressure. Aircraft launched with catapults from aircraft carriers must take off with fuel systems in high boost or the engine will starve for fuel. High g-factor launches coupled with wheel stands increase the demands on fuel systems whether the application is for Pro Street, Stock, Bracket or Pro Stock.
Is it necessary to plumb your system for a return line to the fuel tank?
Yes, because all MagnaFuel pumps are equipped with external bypass system. We don't think that any well-engineered racing fuel system should use internal bypasses because all they do is heat up and add foam (bubbles) to the fuel. It is a little more difficult to plumb, but it provides a better and more efficient system. See the drawings in the Kits section for proper placement of the return line in the tank.
How important is the size of the tank vent?
Attention to this detail may make the difference between winning and losing. It should be equipped with a filter so that trash and dirt cannot enter the fuel system. Absolute minimum size vent is -6 AN, but -8 AN is preferred for any application over 600 hp. Some specialty applications actually need a -10 AN. MagnaFuel rollover/vent (MP-3125) is -8 AN and provides some safety benefits if the vehicle flips over.
How can you check a system for flow and pressure?
Free-flow ratings of racing fuel systems are a joke, so MagnaFuel stresses that the only way to test a system is AT RATED PRESSURE. MagnaFuel rates all its systems at FLOW vs. PRESSURE. Have a fire extinguisher handy. Observe safe practices when dealing with fuel. NO Smoking. You will need an accurately scaled jug (semi-clear polypropylene is ideal) of at least one gallon capacity. One gallon = 128 fluid ounces. One gallon = 4 quarts. One gallon = 231 cubic inches. You need to test the complete fuel supply system, so this measurement will be after regulated control. You will need a stop watch or a watch with a second counter. You will need to provide a variable orifice (brass draincock or petcock works well) for attachment to the end of the fuel line. Run the test at various fuel pressures (regulated flow) and you will learn what your system can do. Use the previous example under fuel system planning. This is particularly important for nitrous enrichment fuel applications so that you will know the result of changing the fuel pressure ¼ psi at a time.
Proper Electrical Supply: The DC electric motors in electric fuel delivery systems are dependent on consistent electric supply. They require good battery voltage, solid connections, proper wire gauge, good ground and a properly operating alternator.
Debris in System: Fuel delivery systems are composed of valves, seals, diaphragms and orifices. Dirt and other debris can disrupt the proper operation of these components. A clean system is imperative. Clean or change your filters often, and periodically check the system for debris. If you are about to install a new system, make sure you clean all installation trash out of the fuel lines. Pay close attention to stainless steel lines.
Voltage Step-down Devices: Never use step-down devices (voltage reduction boxes) on MagnaFuel fuel pumps. Never operate any electric motor on lower voltage than the motor was designed for. Low voltage can cause motor fluctuation and excessive amp draw. MagnaFuel recommends 12.5V and higher
Gauges: Gauges are tuning tools only, and should be removed from vehicle during racing conditions.
Air in System: Any air going into fuel pump on the intake side causes the fuel to foam. Foam will create fluctuation in regulated pressure, oscillation in the pump motor and lean air/fuel mixture. Poor seals on the inlet side fittings, poor placement of the fuel pickup and/or return lines can cause this problem. Return line to fuel cell should be as far as possible from the pick up line fitting.
Fuel Cell Vent Size: If the fuel cell vent is too small, it can cause excessive load and heat in the pump. You should run a minimum of a #8 vent for all applications.
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