Fuel System Sizing Calculator
Enter your target power and engine parameters to get the minimum AN fuel line size, pump flow rating, and injector sizing — for petrol, E85, or E100. Includes BSFC-based flow calculation with configurable safety factor.
AN Line Size
Calculates minimum AN supply and return line diameter based on flow velocity targets.
Pump Flow Rating
Minimum fuel pump LPH rating including safety headroom, at your rail pressure.
Injector Sizing
Per-injector cc/min at 80% duty cycle across your cylinder count and fuel type.
E85 & E100 Support
Automatically scales fuel volume demand for ethanol blends vs petrol.
Engine Parameters
Use maximum power figure, not daily driving power.
Petrol NA: 0.42–0.48. Turbo: 0.50–0.60. High-boost race: 0.65+
System Parameters
Port injection: 43–58 PSI. Direct injection: 1500–3000 PSI (use 58 for pump sizing).
1.25 = 25% headroom. Use 1.30+ for boost applications.
Calculated Results
Minimum Supply Line
AN-4
Bore ID: 6.35mm / 0.250"
Minimum Return Line
AN-3
Bore ID: 4.76mm / 0.187"
Fuel Flow
271 LPH
71.7 GPH
With Safety Margin
339 LPH
×1.25 factor
Min Pump Rating
424 LPH
at rated pressure
Injector Size
1413 cc/min
per injector (4 cyl @ 80% DC)
Flow lb/hr
200.0 lb/hr
total demand
Flow cc/min
4523 cc/min
total demand
Supply Bore
6.35 mm
0.250"
Return Bore
4.76 mm
0.187"
Quick Presets
BSFC Reference Guide
| Application | BSFC (lb/hr/hp) | Fuel | Notes |
|---|---|---|---|
| Street NA (petrol) | 0.42–0.48 | Petrol | Well-tuned modern EFI engine |
| Street turbo (moderate boost) | 0.50–0.55 | Petrol | 8–15 PSI boost |
| High-boost turbo | 0.58–0.65 | Petrol | 20–30 PSI, rich AFR for safety |
| Race engine (large cam) | 0.55–0.70 | Petrol | Poor BSFC at partial load |
| E85 street turbo | 0.65–0.75 | E85 | Approx 35% more volume than petrol |
| E100 / methanol | 0.70–0.85 | E100/Meth | Approx 55% more volume than petrol |
Fuel System Design Notes
Understanding BSFC
BSFC (Brake-Specific Fuel Consumption) is the mass of fuel burned per unit of power per unit of time. A well-tuned NA petrol engine typically runs 0.42–0.48 lb/hr/hp. Turbo engines run richer for safety (0.50–0.65). If in doubt, use 0.55 for a safe street turbo estimate.
Why AN-6 for most builds?
AN-6 (9.53mm bore) is the standard fuel supply for most cars up to ~500hp on petrol. Flow velocity stays within the 2–4 m/s optimal range. Under-sizing a fuel line is the most common cause of lean conditions under load — always go one size up if in doubt.
E85 volume requirements
E85 has ~33% lower energy density than petrol. To make the same power, the engine burns ~35% more volume of fuel per hour. This means a pump and injectors sized for 400hp petrol will only support ~300hp on E85 — always resize everything when converting.
Injector duty cycle warning
This calculator sizes injectors to 80% maximum duty cycle — the practical limit before fuel atomisation and injector cooling degrades. At 100% DC the injector is wide open with no pulse modulation; the ECU has no control headroom. For track or drag use, keep peak DC below 85%. Daily driven cars should stay below 80%.