What size fuel pump does
a 4 cylinder turbo charged engine require to make 500 HP to the crank at 30
PSI?
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:
Normal Aspirated Engines is .45 - .5
Supercharged Engines is .55 - .60
Turbo charged Engines is .6 - .65
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 threw 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 47.5 gal/hr at 78.5 PSI.
From the selection chart on the bottom we
can see that a Walbro high pressure 255 ltr/hr at 13.5 volt will supply enough fuel for the HP
requirement
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