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Fuel System Calculators

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Welcome to our fuel system calculators. Our calculators are very simple. These pages contain basic formulas, input fields, output values, and maybe a basic description, However we won't go into detailed explainations on the theory and basis behind the calculations, or functions here. However we may write some informational articles on them if there is interest, but these calculator pages are all business.

How to use the calculators: Enter your values in the boxes labeled above the calculation button. The calculations will appear in the boxes below the calculation button once the button is pressed, so the final calculated values are only correct when ALL your values are entered correctly.

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BSFC (Brake Specific Fuel Consumption) -

BSFC is basically a measurement of how efficiently an engine is able to use the energy from the fuel it burns. These values are measured on an engine dynomometer under wide open throttle conditions. The formula for BSFC is:

Typical values for BSFC on various modern engines are:
0.48 - 0.55 = Stock and mildly modified performance engines
0.45 - 0.50 = Performance engines with quality heads
0.28 - 0.45 = Racing engines
0.35 - 0.38 = Pro stock engines
0.55 - 0.60 = Supercharged engines
0.55 - 0.65 = Turbocharged engines

Observed HP:

Observed Fuel Flow (lb/hr):

Calculated BSFC:

Selecting the Correct Fuel Injector Size -

Fuel injectors flow a certain amount of fuel. In order to determine what size injector is correct for your application, you need to know what the estimated horsepower output of the engine will be, the engine's BSFC (see the typical values in under the BSFC description above, naturally aspired engines are typically around .50), the number of injectors that will be used on the engine, and the maximum duty cycle for the injectors (typically 80% max duty cycle is recommended). if you want to learn more about injectors, see our series on fuel injectors.

The Formula for calculating the proper size of injectors to use is:

To estimate the size of injectors needed to run E85 or flex fuel vehicles, it isn't quite as easy for various reasons. But E85 fuel requires approximately 47% more fuel to deliver the correct air to fuel ratio for combustion. So using the same injector formula above, to calculate the injector size for E85, the final value is then multiplied by 1.47 to get the approximate E85 fuel injector size needed.

Estimated Horsepower:


Number of Injectors:

Maximum Duty Cycle (%):

Proper Minimum Injector Size (lb/hr):

Estimated Minimum Injector Size for E85 Fuel (lb/hr):

Injector Flow Horsepower support -

How much horsepower will a certain flowing set of injectors support? use this calculator to find out. remember to use the ACTUAL flow of the injectors for your fuel system pressure, which may or may not be different from the pressure the injector is rated at. the formula to find the HP support for a set of injectors requires the total number of injectors being used, the injector flow rate (in lbs/hr), the BSFC of the engine they will be used on (see general values in the BSFC description above), and the max duty cycle the injectors will experience (typically 80% max duty cycle is recommended).

The formula for calculating a fuel injector set horsepower support is:

Fuel injector Flow Rate (lbs/hr):

Max Duty Cycle (%):


Total Number of Injectors:

Calculated Fuel Injector Horsepower Support:

Injector Flow Change with System Fuel Pressure Change -

When you change the fuel system pressure, you also change the flow rate of the injectors. To calculate the change in the injector flow rate based on a change in the fuel system pressure change, you need to know the old fuel pressure, new fuel pressure, and what the fuel injector flow rate was at the old fuel pressure. The formula for calculating the flow rate change is:

This formula will work for any measurement units that you want on both the fuel pressure (BAR, PSI, etc..) and injector flow rate (lb/hr, cc/min, g/s, etc), however you MUST use the same units for both old and new fuel system pressure, and the calculated new injector flow rate will be the same units as whatever you use for the old injector flow rate.

Old Fuel System Pressure:

New Fuel System Pressure:

Old Injector Flow Rate:

New Fuel Injector Flow Rate:

Fuel Pump Capacity - In order for the fuel injectors or carb to supply the required fuel for the engine, they require a steady and consistant supply of fuel from the fuel pump. The required fuel flow from the pump varies depending on the application setup. The calculators below will calculate the required fuel pump flow to support your fuel injectors, or carb fuel flow.

Fuel Pump Flow Rate (Fuel Injection) -

The formula for calculating the required fuel pump flow for a fuel injected engine will depend on the flow rate of the injectors and number of injectors.

Fuel Injector Flow Rate (lb/hr):

Number of Fuel Injectors:

Injection Fuel Pump Flow Rate (Gal/hr):

Fuel Pump Flow Rate (Carb) -

The formula to calculate the fuel pump requirements for a carb are less precise but similar as the fuel injection calculations, however it is calculated with the engine's horsepower and BSFC.



Carb Fuel Pump Flow Rate (Gal/hr):

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