Calculating fuel injector size involves several factors, including the engine’s horsepower, fuel pressure, and the number of injectors. The most common formula used for this calculation is based on brake-specific fuel consumption (BSFC), which is the amount of fuel required to produce one horsepower for one hour. Here’s a basic formula to calculate fuel injector size:

  • Injector Size is the flow rate of the fuel injector in pounds per hour (lb/hr).
  • Horsepower is the engine’s estimated or measured horsepower.
  • BSFC is the brake specific fuel consumption, typically given in lb/hp/hr. You can find average BSFC values for different types of engines, with turbocharged engines generally having higher values than naturally aspirated engines.
  • Number of Injectors is the total number of injectors you plan to use.
  • Injector Duty Cycle is the percentage of time the injector is open during each engine cycle. A common value is around 80%.