You can read more here about sizing your fuel pump to horsepower but it varies based on the model, flow rate and pressure a given pump will support. Fuel pumps are typically rated in liters per hour (LPH) according to their ability supply fuel at a certain pressure. At 43 PSI (3 Bar), that same 255 LPH pump will support up to be about 500 horse power and is suitable for both racing conditions or those more demanding direct replacements.
The value of the fuel pressure is involved in this calculation. The fuel pump gets more heavy the higher the pressure. At 60 PSI, the same 255 LPH fuel pump likely can support only about 450 horsepower since pressure increases reduce flow. The capacity of the fuel pump is calculated by determining how much all 8 cylinders will drink at full power. Most high-performance engines will need at least 400 LPH of fuel flow, and for those engines topping the 600-horsepower mark this number can rise well above that level.
The pump from Walbro comes in the form of 450 LPH and is very well known among the world on a modified street car or racing purposes. The A750 is rated to work with engines running on gasoline for up to 700 horsepower, but since E85 requires about a third more fuel flow than gas its capacity falls back down around the 500 mark. This is an example of how type of fuel changes the amount HP you are able to support via a single pump
That year, a few of those same enthusiasts had trouble during the Pikes Peak International Hill Climb when high-altitude, high-stress conditions created fuel delivery problems that sapped power. Real world examples demonstrating why you need to choose a fuel pump with plenty of headroom to handle wide variances in pressure, some altitude and engine load.
To paraphrase the founder of Hennessey Performance, John Hennessey himself: more horsepower requires more fuel, and if your pump can’t keep up with either… well. A fuel pump that can support the horsepower output your engine is essential to both maintaining performance and avoiding some verging on stall situations from being attributable to a starving fuel system.
To read more fuel pump news go to Fuel Pump.