Injector Size Selection

Matching the Injector to the Engine

To calculate the injector size for a particular application:

Injector Flow Rate (lb/hr) = Engine HP(1) x BSFC(2)
Number of Injectors x Injector duty cycle(3)

Or

Injector Flow Rate (cc/min) = Engine HP(1) x BSFC(2) x 10.5
Number of Injectors x Injector duty cycle(3)

This worksheet can do the calculations for you:

Fuel Injector Size Worksheet

Engine Horse Power(1):
BSFC(2):
Number of Injectors:
Injector duty cycle(3):

Flow Rate: Lb/Hr     cc/min

This Size Selection Guide is intended to help in determining what size injector to use in your application.
* Brake Specific Fuel Consumption: This is the amount of fuel consumed (in lbs. per hour) for each horsepower made.
This should be .45 to .50 for naturally aspirated engines
Supercharged engines should be between .55 to .60
Turbocharged engines.60 to .65
Rotary engines, estimate BSFC to be 0.6 to 0.7
For engines running methanol, double the appropriate gasoline BSFC (e.g. a rotary engine running methanol has a BSFC between 1.2 and 1.4)
** Maximum Injector Duty Cycle should be around 80% max for safe operation. This allows for some future horsepower increases.