Fuel Injector Sizing Calculator
Size injectors (lb/hr, cc/min) for target HP — gas, E85, methanol, or diesel, with BSFC and safe max duty.
How to Use
- Enter HP target, number of injectors (usually = cylinders), fuel, and BSFC.
- Set max duty cycle — 80% street, 85% race. Past 90% flow turns non-linear.
- Result: required lb/hr and cc/min per injector.
Target
Injector size
Formula
Required flow
lb/hr = HP · BSFC / (N · duty)
cc/min
cc/min = lb/hr · 10.5 (gas @ 6.21 lb/gal)
Frequently Asked Questions
BSFC numbers?
NA gas 0.45-0.50. Turbo gas 0.55-0.65. E85 0.65-0.80. Methanol 1.0-1.2. Diesel 0.35-0.42.
Why 80% max duty?
Past ~85%, injector flow becomes non-linear — pintle stays open, latency matters less. Tuning gets harder.
Static vs dynamic flow?
Static = full-open flow. Dynamic = average at pulse-width. Tuners use static; dynamic is 5-15% less depending on dead-time.
Common Use Cases
Turbo build
Match FIC/ID/Bosch injectors to HP and fuel.
E85 conversion
Typical uplift is 1.3-1.4× gas flow. This tool nails the ratio.
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