Size your injectors.
Enter your power goal, fuel and pressure to see the flow you need, or check what your current injectors can support.
Advanced
Your setup, across the lineup.
| Injector | Flow at your pressure | Crank hp | Wheel hp |
|---|
The math, out in the open.
Fuel pressure correction
Injector flow changes with the square root of the pressure across it. With a boost referenced regulator the pressure across the injector stays at base pressure. With a non-referenced or returnless system it drops by the boost pressure.
flow at pressure = rated flow × √(differential pressure ÷ rated pressure)
Fuel type and ethanol content
Each fuel is calculated from its own stoichiometric ratio and density, so blends are handled properly instead of using one fixed multiplier. Gasoline 14.7:1 at 0.74 kg/L, ethanol 9.0:1 at 0.789 kg/L, methanol 6.45:1 at 0.792 kg/L. Ethanol blends are mixed by volume and converted to mass.
fuel BSFC = gasoline BSFC × (14.7 ÷ fuel stoich) × (0.80 ÷ target lambda)
BSFC by aspiration
Gasoline equivalent BSFC of 0.50 for naturally aspirated, 0.60 for supercharged and 0.65 for turbocharged engines, in lb per hp per hour. These are conservative starting points. Enter your own value under Advanced if you have dyno data.
Horsepower and fuel system
crank hp = (flow at pressure × density × cylinders × duty cycle) ÷ fuel BSFC
Wheel horsepower subtracts the drivetrain loss you select. Fuel system demand is the total injector flow at your duty cycle, which your pump needs to supply at base pressure plus boost.
Duty cycle and redline
At 4 stroke, an injector has one full engine cycle (two revolutions) to deliver fuel. At 8000 rpm that is 15 ms. The calculator defaults to 95% maximum duty. Going past that leaves almost no room for fuel temperature, voltage and tune changes. Results are estimates. Final fueling should always be confirmed on a dyno with a wideband.