Calculating Fuel RequirementsBy Chris Myer
Answers questions such as:
How much fuel pump do I need?
Now, if you're just trying to replace a faulty fuel pump, don't read this. The Walbro standard-performance fuel pumps that are available for all vehicles provide more than adequate fuel to meet your needs. However, there are some folks out there who have significantly modified their vehicles (significant being much more than an intake and exhaust) and those folks really need to consider a highe performance fuel pump. If that's you, read on.
Determining how much fuel your fuel pump needs to be able to provide is no mystery. It's simple mathematics. The engine in your car takes in air and fuel and converts them to horsepower. The amount of horsepower your engine can make is a function of things like the size of the engine, the compression ratio, the boost (in turbo/super-charged applications) and several other variables. To make this horsepower, your engine will consume a certain amount of fuel. That amount is referred to as the "Brake Specific Fuel Consumption", or BSFC. The BSFC is generally estimated to be between 0.45 and 0.50 for most naturally-aspirated (non-turbo/super-charged) engines, and between .55 and .60 for turbo/super-charged engines.
We used to go through all of the mathematical conversions but most folks just want the bottom line, so here is what we suggest. Multiply horsepower by .38 (naturally-aspirated motors) or .47 (force-induction motors) to come up with a fairly accurate guide to how many liters per hour of fuel you will need to feed the engine. For example, if you are building a really hot little 4 cylinder turocharged engine and plan to make about 450HP, you would need a fuel pump that can produce about about 212 liters per hour (450 * 0.47). Looking at it the other direction, the Walbro 255 liter per hour fuel pumps that we sell as part of the high performance fuel pump kits on this website are capable of feeding a turbocharged engine making up to about 540hp, or a naturally aspirated motor up to about 670hp.
It is critical that the fuel pump in your fuel-injected vehicle is able to produce at least as much or more volume over time than the engine requires. If the fuel pump is unable to meet the fuel requirements then the fuel mixture will become lean and the engine will go into pre-detonation and will eventually destroy itself. Unfortunately, many stock fuel pumps are capable of providing enough fuel for only the capabilities of the engine as designed and installed by the manufacturer. Users who seek higher horsepower output from their vehicles increase fuel requirements. The stock fuel pump often becomes dangerously inadequate to provide fuel to the heavily modified engine. Since additional flow above engine requirements will simply be returned to the fuel tank, too much flow is a far better thing that too little.