Fuel pump upgrade is about step 10 in our DSM upgrade path. Before upgrading anything radical, like the turbo or fuel injectors, you need to make sure you have a pump that can keep up with your fuel needs. Like injectors, you can get a pump with more capacity that what you currently need so you won’t have to upgrade again. The most common upgrade fuel pumps are the Walbro 190 and 255. The number describes the volume output in liters per hour (lph). The Walbro pumps also come in models designated “high pressure”. These are worth looking into because typically they don’t cost much more and they make a big difference above 25 psi boost. The size of the pump you choose should be based on your current or future horsepower goals.
The equation to estimate fuel consumption by horsepower output is as follows:
HP x BSFC(0.65) = fuel use in lb/min x 0.0107 = liters per minute x 60 = lph
Or, you can skip all the middle stuff and multiply HP x 0.42 to get lph. Example:
250hp x 0.42 = 105 lph
Conventional wisdom is that the pump should be adequate to supply the rate required for maximum horsepower output
plus 20%. Here is a table of calculated rates:
HP…..lph…..lph + 20%
250….105….126
300….126….151
350….147….176
400….168….202
450….189….227
500….210….252
Do I need an adjustable fuel pressure regulator?
Most agree that an adjustable FPR is not required for a 190 lph pump but is required for a 255 lph pump. A 255 lph pump may produce more fuel flow than the stock FPR can deal with. This is known as fuel overrun and it is likely to cause an excessively rich fuel mixture.
Flow rate decreases with fuel line pressure.
A fuel pump’s flow rate is constant at a given voltage and pressure. As fuel line pressure increases, the rate slows as the pump works harder. Standard line pressure for a 2g is 43.5 psi, which is controlled by the fuel pressure regulator (FPR), 36.3 psi for a 1g. When under boost, the FPR increases the fuel pressure by the same amount to maintain the pressure differential at the injectors. At 20 psi boost, the actual line pressure is 63.5 psi (2g dsm) and the output capacity of the fuel pump is reduced. Be sure the pump you choose can maintain the flow rate at the highest boost level you will use. Many pumps have flow rate charts available.
Flow rate increases with higher voltage.
One of your first mods should be fuel pump rewire. Without rewiring, the voltage that reaches the pump may be less than 12V. With 10 gauge rewire, the voltage is about 14.5V and output increase is significant.
Below is a graph of the four common pumps (Walbro 190, 190 HP, 255, 255 HP) at 12V and 14.5 V.
Note: I'm not a Walbro salesman but due to their popularity, there's a lot more data available.
Reference:
Walbro In-tank, high-pressure Fuel Pump Specs
Ron Tew
