Fuel & Tuning
Fuel Injector & Pump Sizing
Size injectors (cc/min & lbs/hr) and minimum fuel-pump flow for gasoline or E85 across NA and boosted power goals.
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How to Use This Tool
- Enter target horsepower for the finished tune.
- Select cylinder count, fuel (Pump 93 or E85), and aspiration.
- Keep max duty cycle near 80–85% for street reliability.
- Round up to the next common injector size and verify pump LPH at your rail pressure.
The Formula & Physics Behind the Math
BSFC (brake specific fuel consumption) estimates fuel mass per horsepower-hour. Gasoline NA ≈ 0.50, boosted ≈ 0.62; E85 NA ≈ 0.70, boosted ≈ 0.85. Total fuel lbs/hr = HP × BSFC. Injector size = total fuel ÷ (cylinders × duty cycle). Convert lbs/hr to cc/min with × 10.5. Pump LPH ≈ (lbs/hr ÷ 6) × 3.785 × 1.2 safety margin.
Frequently Asked Questions
Should I size for crank HP or wheel HP?
Use the horsepower the injectors must support at the flywheel. If you only have WHP, add estimated drivetrain loss before sizing.
Why is E85 needing bigger injectors?
Ethanol carries less energy per pound and typically runs richer AFR targets, so BSFC rises and injector flow demand jumps 30–40% versus pump gas.
Is 85% duty cycle safe?
Most street tunes stay under 80–85% peak duty. Race setups may run higher with supporting fuel system and careful monitoring.