Fuel Pump Sizing

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Fuel pump sizing on your performance engine is critical!

What size fuel pump does a 4 cylinder turbo charged engine require to make 500 HP to the crank at 30 PSI with race gas?

This should only be seen as a basic guide to fuel pump selection. With a little knowledge and data, selecting a fuel pump for your horsepower delivery becomes fairly straight forward.

Weight of fuel:

The average advertised weight of a gallon of premium fuel is 6.34 lb/gallon.

Brake Specific Fuel Consumption or B.S.F.C.

Brake Specific Fuel Consumption or B.S.F.C. is the amount of fuel required to produce 1 HP for 1 hour. This means that an engine with a B.S.F.C of .5 will burn 1/2 or .5 lbs of fuel to produce 1 HP for one hour. Determining exact B.S.F.C for a specific engine is complicated and requires an engine dyno.

Based on industry standards the B.S.F.C for:

Naturally Aspirated:
Gasoline – .45 to .50
E85 – .63 to .70
Methanol – .9 to 1.0

Boosted or forced induction:
Gasoline – .60 to .65
E85 – .84 to .91
Methanol – 1.80 to 2.0

 

Fuel Pump Pumping Losses:

Fuel pump pumping losses is the difference in fuel pressure measured at the fuel pump exit and that of the fuel pressure at the exit of the fuel rail. Friction, fuel line inside diameter and turns or bends in the fuel line is the cause of the pressure difference which can be as high as 4 – 10 PSI.

Fuel Pressure Regulator or FPR:

A fuel pressure regulator or FPR is a piece of equipment that mechanically or electronically controls fuel pressure. Without getting to technical, the FPR’s purpose is to raise or drop the fuel pressure from a preset point by the same amount the pressure in the intake manifold changes. Lets say the FPR is set to a base pressure of 43.5 PSI and the manifold pressure goes up by 10 PSI the FPR now should control the fuel pressure at 54.5 PSI.

About injectors and boost:

Most fuel injector flow rates are advertised statically at 43.5 PSI. This means that fuel flow is measured while the injector is kept fully open and fuel is pumped through the injector at a pressure of 43.5 PSI into atmospheric. To maintain advertised flow rates the fuel pressure should be raised or dropped by the same amount the pressure in the intake manifold raises or drops. If static fuel pressure is set to 43.5 PSI and manifold pressure raises to 30 PSI fuel pressure should rise to 43.5 + 30 = 73.5 PSI. Max HP supported by an injector is calculated to flywheel power.

How much fuel do I need for a 4 cylinder turbo charged engine making 500 HP to the crank at 30 PSI?

First we need to calculate total fuel pressure. Lets say the measured pumping loss is 5 PSI

(Base fuel pressure) + (Total Boost) + (Pumping Loses) = Total Fuel Pressure required

43.5 + 30 + 5 = 78.5 PSI

Now we need to calculate fuel required:

Target Hp * B.S.F.C. = Fuel required in lbs/hr

500 *.6 = 300 lbs/hr

Most fuel pumps flow rate is advertised in gallons per hour:

Lbs/hr / fuel weight per gallon = gal/hr

300 / 6.34 = 47.32 gal/hr

To make 500 crank HP at 30 PSI of boost we need a fuel pump that will be able to supply at least 47.5 gal/hr at 78.5 PSI.

From the selection chart on the bottom we can see that a Walbro high pressure 255 l/hr at 13.5 volt will supply enough fuel for the HP requirement.

Walbro Fuel Pump Specs.

Walbro fuel pump flow rates and current draw at 12 volts

PSI190 ltr/hr
fuel pump
(gal/hr)
190 ltr/hr
fuel pump
(amps)
“high pressure”
190 ltr/hr pump
(gal/hr)
“high pressure”
190 ltr/hr pump
(amps)
255 ltr/hr
fuel pump
(gal/hr)
255 ltr/hr
fuel pump
(amps)
“high pressure”
255 ltr/hr pump
(gal/hr)
“high pressure”
255 ltr/hr pump
(amps)
0562.6532.8754.7764.4
10523.2503.5725.2734.8
20484.0484.3676.1685.5
30444.8445.0627.2636.3
40405.7415.9588.2597.1
50366.6386.8539.3548.0
60327.6357.84910.6518.9
70288.6318.84011.8469.9
80229.7299.92913.34111.0
901210.82510.9014.63212.0
100012.52112.02213.2
1101713.51114.5
1201115.0115.8

Walbro fuel pump flow rate and current draw at 13.5 volts

PSI190 ltr/hr
fuel pump
(gal/hr)
190 ltr/hr
fuel pump
(amps)
“high pressure”
190 ltr/hr pump
(gal/hr)
“high pressure”
190 ltr/hr pump
(amps)
255 ltr/hr
fuel pump
(gal/hr)
255 ltr/hr
fuel pump
(amps)
“high pressure”
255 ltr/hr pump
(gal/hr)
“high pressure”
255 ltr/hr pump
(amps)
0633.1603.3825.2855.0
10613.5583.9815.9825.2
20574.2564.5766.5796.0
30525.0525.3717.8736.8
40495.8506.2688.6707.5
50466.6477.2629.8658.2
60427.5458.05810.8619.1
70388.4418.85012.05610.2
80329.4389.83913.35111.1
902210.33410.91114.44312.1
1001411.53112.0115.03213.2
11012.72813.22014.3
1202214.51115.7
1301816.017.0