Getting fuel delivery right is what separates a safe tune from a melted piston. This calculator helps you size injectors based on your engine’s power goals, fuel type, and system setup — no guessing, just solid math. Enter your target horsepower, base fuel pressure, duty cycle, and cylinder count, and it instantly estimates the injector flow each cylinder needs.
The tool factors in different fuels and aspiration types, adjusting BSFC automatically so you can see how gasoline, E85, or methanol change the numbers. You can even add a safety margin or manually enter BSFC if you’re fine-tuning for a specific engine.
Results are displayed in both cc/min and lb/hr, using a precise 10.23 cc/min per lb/hr conversion based on real pump-grade gasoline density. Whether you’re dialing in a turbo Subaru, building a custom EFI setup, or just checking if your injectors are up to the task — this tool gives you real answers before you ever touch a wrench.
Required per injector (cc/min @ Bar / PSI)
This is the minimum injector flow each injector must supply at your chosen base fuel pressure, after accounting for engine horsepower, BSFC, duty cycle, and your safety margin.
Choose an injector size that meets or exceeds this cc/min rating at the same pressure in the injector’s datasheet.
Injector duty cycle (%)
This is the maximum percentage of each engine cycle that the injector is allowed to stay open.
Running injectors at 100% duty is unsafe; values around 80–90% give a buffer for real-world variations, transient enrichment, and future power increases.
Safety factor (%)
The safety factor adds extra capacity on top of the theoretical requirement.
This covers things like dirty filters, low voltage, hot fuel, and small power upgrades without immediately needing larger injectors.
BSFC (Brake Specific Fuel Consumption)
BSFC is how many pounds of fuel per hour your engine needs per horsepower.
The calculator can estimate BSFC from engine aspiration and fuel type, or you can override it manually in the advanced section if you have dyno data or specific build knowledge.
BSFC (Brake Specific Fuel Consumption) tells you how much fuel mass an engine burns to make one horsepower for one hour — measured in lb/hp/hr.
Lower BSFC = higher efficiency. Turbo and supercharged engines run richer for cooling and detonation control, so their BSFC is higher.
Different fuels carry different energy per kilogram. Gasoline is our baseline at about 43 MJ/kg, while E85 has roughly 30 MJ/kg, and methanol sits near 20 MJ/kg.
That’s why E85 engines need about 20–30 % more fuel flow and methanol engines nearly twice as much to make the same power. The calculator models this automatically by adjusting BSFC when you change fuel type.
When BSFC is multiplied by horsepower, it gives total fuel mass flow, which is then converted into injector flow (cc/min) using the fuel’s density.
For gasoline, the conversion factor is 10.23 cc/min per lb/hr — derived from its real density of 6.17 lb/gal at 60 °F.
Many charts use 10.5 instead, assuming a round 6.0 lb/gal, but 10.23 reflects true pump-grade gasoline and keeps results physically accurate rather than rounded.
Enter your values to calculate.
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