Fuel Injector Flow Rate Calculator
Enter your desired engine horsepower and the specs of your motor to calculate the recommended fuel injector flow rate.
Recommended Injector Flow Rate:
Gasoline
Race Gas
E85
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Joe is the creator of Inch Calculator and has over 20 years of experience in engineering and construction. He holds several degrees and certifications.
How to Find the Right Fuel Injector Flow Rate
Getting the right amount of fuel to an engine is crucial to maximizing the performance of the motor and optimizing the benefits from other performance modifications. So, getting the right size fuel injectors is an important step when tuning the performance of a vehicle.
It’s important to bear in mind that using a fuel injector that’s too large will choke the vehicle with too much fuel. Using fuel injectors that are too small will run too lean and starve the motor.
Follow these easy steps to choose just the right size fuel injectors for your motor.
Step One: Determine the Target Horsepower
How much power do you realistically expect the engine to output? You can find a realistic estimate by adding the expected horsepower gains from other modifications you’ve made to the stock engine horsepower.
You might also want to try our engine horsepower calculator.
Step Two: Calculate the Brake-Specific Fuel Consumption
Brake-Specific Fuel Consumption, or BSFC, is a ratio of the amount of fuel consumed to the amount of power output. This will vary based on the type of fuel being run and the engine aspiration. You can calculate the BSFC for your engine, or estimate it using the fuel type and aspiration.
Refer to the following chart for average brake-specific fuel consumption values.
| Fuel Type | Aspiration | BSFC |
|---|---|---|
| Gasoline | Naturally Aspirated | 0.5 |
| Supercharged | 0.55 | |
| Turbocharged | 0.6 | |
| Race Gas | Naturally Aspirated | 0.545 |
| Supercharged | 0.5995 | |
| Turbocharged | 0.654 | |
| E85 | Naturally Aspirated | 0.667 |
| Supercharged | 0.733 | |
| Turbocharged | 0.8 |
Step Three: Find the Motor’s Safe Duty Cycle
The safe duty cycle is the percentage of time the fuel injector is open in the cycle. Most stock engines should use a safe duty cycle of 80%, and engines with performance modifications can run at 85-90%.
Step Four: Calculate the Ideal Injector Size
Now that the target horsepower, BSFC, and safe duty cycle have been found, it’s possible to calculate the ideal fuel injector size. Use the following formula to calculate the proper flow rate for your injectors.
injector flow rate = horsepower × BSFC / num cylinders × duty cycle
To find the ideal flow rate, simply plug in the values found in steps one, two, and three into the formula and solve.
The result will be the flow rate in lb/hr. To get the result in cc/min use a lb/hr to cc/min conversion calculator.
For example, let’s find the fuel injector size for a turbocharged V8 motor that we want to run at 450 horsepower, assuming we’ll run normal gasoline.
The BSFC for this setup will be 0.6 according to the chart above. Let’s enter the values into the formula.
injector flow rate = 450 × 0.6 / 8 × 85%
Now, let’s solve it.
injector flow rate = 270 / 6.8
injector flow rate = 39.706 lbs/hr
You should also check out our compression ratio calculator.