BSFC (Brake Specific Fuel Consumption) is how much fuel an engine uses per horsepower per hour. Typical values are 0.45–0.50 for naturally aspirated engines and 0.55–0.65 for forced induction.
A lower BSFC means the engine is more efficient. Turbocharged engines often run richer (higher BSFC) for cooling and knock protection.
The calculator gives you the minimum injector size. In practice, always round up to the next available injector size and leave headroom. Running injectors at 100% duty cycle leaves no margin for error.
Common injector sizes: 440 cc/min, 550 cc/min, 650 cc/min, 750 cc/min, 850 cc/min, 1000 cc/min, 1300 cc/min.
Fuel injector sizing is critical for performance engine builds. Undersized injectors cause lean conditions that can destroy pistons, while oversized injectors make tuning difficult at idle and low loads.
The formula used is: Injector Size = (HP × BSFC) / (Number of Cylinders × Duty Cycle). This gives the flow rate each injector must support to feed your engine safely.
For boosted engines, always use a higher BSFC (0.55–0.65) and keep duty cycle under 85%. Turbocharged engines need more fuel for both power and cooling, so injector headroom is essential.
For a 4-cylinder engine making 500 HP with a BSFC of 0.60 and 80% duty cycle, each injector needs to flow approximately 750 cc/min (70 lb/hr). A 6-cylinder engine would need roughly 500 cc/min per injector for the same power.
Yes. Injectors that are too large make it difficult to achieve proper fueling at idle and low loads because the minimum pulse width may be too short for precise control. A good rule of thumb is to size injectors so you reach your max power at 75-85% duty cycle.
cc/min measures volume flow rate of fuel. lb/hr measures mass flow rate. Since fuel density varies slightly with temperature, lb/hr is technically more accurate. Most tuners and manufacturers provide both ratings. 1 lb/hr ≈ 10.5 cc/min.
Boosted engines need significantly larger injectors because more air requires more fuel to maintain the correct air-fuel ratio. Every pound of boost adds roughly 3-4% more fuel demand. A turbocharged engine at 10 PSI may need 30-40% more injector capacity than the same naturally aspirated engine.
Most tuners recommend keeping peak duty cycle below 85% to maintain safe injector operation. At 90% or higher, injectors may not have enough time to fully open and close, leading to inconsistent fuel delivery.