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Basic Calculations

What HP Can Your Fuel System Support?

HP*lb/hr This is your Brake Specific Fuel Consumption. 0.62 is an empirically supported estimate for modified, stock-turbo 13B-REW engines. See this page for some additional information.
Fuel Pressure:
psi This is the effective fuel pressure, which is your fuel rail/gauge pressure minus the manifold (boost) pressure.
Fuel Injectors:
Bank # cc/min lbs/hr
1 or
2 or
3 or
How many injectors do you have, and how much fuel do they flow at the standard 43.5 psi pressure? Enter values in cc/min or lbs/hr.
Max Duty Cycle:
% This is the maximum duty cycle that the injectors will experience. The stock 93-95 RX-7 ECU tops out around 63%. The recommended maximum value for programmable engine management systems is 80%-85%. Above that, the injectors might stay open, which gives up tuning control.
Drivetrain Losses:
% This is an approximation of the power lost in the transmission, differential, etc. I am not sure what values are appropriate for FWD or AWD cars.
Flywheel HP:
HP With the above components, your fuel system should be capable of providing enough fuel for this amount of flywheel HP. This is comparable to manufacturers' HP ratings.
Wheel HP:
WHP With the above components, your fuel system should be able to supply enough fuel for this amount of HP at the wheels. This is the power that is measured on a chassis dynamometer.

Specify These Additional Parameters to Calculate Fuel Pump Requirements:

Boost Pressure:
psi If your car is a turbo, how much boost are you running? For normally-aspirated cars, enter zero.
Fuel System Pressure Drop:
psi A lot of the fuel pressure generated by the pump can be lost in the restrictive plumbing of the fuel system. This value affects the pressure your fuel pump will be required to supply. See this page for some interesting test data.
Fuel Pump Requirements:
You need a pump that will flow:
L/hr  at psi
Based on the parameters given above, you will need a fuel pump that meets these requirements. It is a good idea to give yourself a little safety margin over and above this requirement.


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