Today's high-performance engines are able to deliver horsepower numbers unheard of 10 years ago. With better-flowing cylinder heads, ignition systems, and camshaft profiles, the potential for huge power is almost endless. Combine this with the strides in chassis development and you have a car that not only makes lots of power, but can get it to the ground with higher g-forces. This month we'll take a hard look at selecting proper fuel pumps, filters, lines, and system components for a carbureted system and follow up it next month with similar principles for fuel-injected appli-cations. Now, whether your forte is drag racing or road racing, a good supply of fuel fed to your engine at the right pressure (under all driving circumstances) is critical to achieving the ultimate performance.
Choose The Right Pump FirstWhen choosing a pump, you'll first need to determine how much power your engine is developing (under full power) at the flywheel and how much fuel will be required to support it. If you don't have actual dyno results, you can estimate your power. For most carbureted systems on street engines developing under 450 horses, an off-the-shelf performance mechanical fuel pump installed to a properly maintained fuel system should work fine. Get into higher horsepower numbers, or add nitrous or a supercharger to your engine, and you'll need a properly installed, significantly stronger electric pump.
You'll also need to know your engine's fuel efficiency, commonly referred to as BSFC (Brake Specific Fuel Consumption), the maximum fuel system pressure, and the pump's flow volume at that pressure. Lastly, on electric pumps you'll need to know the available voltage at the pump under engine load and the pump's flow volume at that voltage. This is very critical; wire a high-dollar electric pump incorrectly, and the pump's performance will suffer and the engine could run lean.
In the absence of actual dyno information, you'll need to first determine how much horsepower will be produced and the amount of fuel required to support it by estimating engine horsepower on both the high side and low side of BSFC. Most gasoline engines use less than 1 pound of fuel to make 1 hp for 1 hour, so expect the BSFC number to be less than 1. Different performance combinations, power-adders, and even fuel-octane ratings and engine tuners will have a great impact on BSFC. In the world of electric fuel pumps, many are flow-rated at zero pressure. Be careful here because your system works under pressure, and pressure will drastically affect how much fuel flow your pump delivers. When shopping for a fuel pump, be sure to look for fuel-flow ratings at the pressure you need.
To estimate your engine's BSFC, use the following guidelines. It's important to note that the best method of establishing actual BSFC is through proper flywheel dyno-testing.
* Naturally aspirated engines are generally most efficient with a BSFC between .45 and .55 lbs/hp/hr.
* Nitrous combinations typically use a little extra fuel and often develop a BSFC from .5 to .6 lbs/hp/hr.
*Forced induction engines are often least efficient, and BSFC ranges from .6 to .75 lbs/hp/hr.
Using 500 hp as an example, we'll show the fuel requirement for two engine efficiency combinations:(HP x BSFC = pounds of gasoline)500 hp x .5 BSFC = 250 pounds of gasoline.500 hp x .75 BSFC = 375 pounds of gasoline.
Since a gallon of fuel weighs about 6.2 pounds, we find that in our first example, 250 6.2 = 40 gph (gallons per hour) and 375 6.2 = 60 gph.