EFI Injector Sizing Calculator
Calculate required injector size from HP and fuel type. Shows lb/hr, cc/min, and the next standard injector size up.
HP figure is:
60% (conservative)80% (recommended max)90% (absolute max)
Required lb/hr
39.1
Required cc/min
410
Next standard size
40.7
440 cc/min
Duty cycle at that size
96.0%
Duty cycle exceeds 90% — the engine will run lean at peak power. Size up to the next injector.
Standard Injector Size Reference
| lb/hr | cc/min | Application |
|---|---|---|
| 14.8 | 160 | Stock economy |
| 19.8 | 214 | Stock import performance |
| 21.7 | 235 | Stock small V8 |
| 25 | 270 | Mild performance |
| 29.1 | 315 | Street performance |
| 34.2 | 370 | Street performance |
| 40.7 ✓ | 440 | Hot street / mild boost |
| 50.9 | 550 | Street/strip boost |
| 58.3 | 630 | High-boost or E85 street |
| 69.4 | 750 | High-power boosted |
| 78.6 | 850 | Race / high-boost E85 |
| 92.5 | 1000 | Race |
| 111 | 1200 | Pro race / extreme boost |
| 153 | 1650 | Dual-fuel or mega-power |
| 199 | 2150 | Extreme applications |
Formula: lb/hr = (HP × BSFC) / (# injectors × duty cycle)
• 80% max duty cycle is the industry standard for reliability. Above 90% the engine runs lean at peak power.
• 1 lb/hr ≈ 10.5 cc/min (gasoline). E85 injectors need ~35% larger flow for the same HP due to higher BSFC.
• Injector sizing is based on crank HP. If you only have wheel HP, divide by 0.85 (RWD) or 0.87 (FWD) for an estimate.