Fuel Injector Flow Rate Calculator
Calculate required fuel injector flow rate (lb/hr or cc/min) from target horsepower, BSFC, number of injectors, and maximum duty cycle.
Required Injector Flow Rate
31.3 lb/hr
cc/min
328
Total System Flow
250.0 lb/hr
💡 Flow = (HP × BSFC) ÷ (Injectors × Duty%) = (400 × 0.50) ÷ (8 × 80%) = 31.3 lb/hr
Typical BSFC by Engine Type
| Engine Type | Typical BSFC |
|---|---|
| N/A Gasoline | 0.45–0.50 lb/HP-hr |
| Turbo Gasoline | 0.55–0.65 lb/HP-hr |
| Supercharged | 0.55–0.60 lb/HP-hr |
| E85 | 0.65–0.70 lb/HP-hr |
| Methanol | 0.90–1.00 lb/HP-hr |
💡 How to Use the Fuel Injector Flow Rate Calculator
How to Size Fuel Injectors
Fuel injectors must supply enough fuel to support the engine's target horsepower without exceeding a safe duty cycle. Undersized injectors run at 100% duty cycle and can't deliver enough fuel; oversized injectors have poor idle quality and atomization.
Example: 400 HP, BSFC of 0.50, 8 injectors, 80% duty: (400 × 0.50) ÷ (8 × 0.80) = 31.25 lb/hr per injector (328 cc/min)
BSFC Guidelines
Brake Specific Fuel Consumption (BSFC) measures fuel efficiency at peak power. Lower BSFC = more efficient.
- Naturally Aspirated: 0.45–0.50 lb/HP-hr
- Turbocharged: 0.55–0.65 lb/HP-hr
- E85 Flex Fuel: 0.65–0.70 lb/HP-hr
- Methanol: 0.90–1.00 lb/HP-hr
Duty Cycle
The duty cycle is the percentage of time the injector is open. At 80% duty, the injector is open 80% and closed 20% of each engine cycle. Never size for more than 80–85% duty — this leaves headroom for fuel pressure fluctuations and ECU corrections.