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Compare tire sizes and calculate overall diameter, speedometer error, and clearance. See how plus-size or downsizing affects gearing and fitment.
Calculate engine horsepower from torque and RPM or estimate from quarter-mile time and weight. Convert between HP, kW, and brake horsepower units.
Estimate 0-60 mph acceleration time from horsepower, vehicle weight, and drivetrain loss. Model realistic launch performance for tuning and comparison.
Total fuel flow equals horsepower times BSFC. BSFC is pounds of fuel per horsepower per hour. Naturally aspirated gas engines use ~0.45–0.50; turbo builds use ~0.55–0.65.
Fuel flow (lb/hr) = HP × BSFCInjectors should not exceed 80–85% duty cycle at peak power to maintain atomization and headroom. Divide total flow by number of injectors and duty cycle limit.
Injector (lb/hr) = (HP × BSFC) / (N × Duty cycle)Gasoline weighs ~6.25 lb/gallon. Convert lb/hr to cc/min for injector ratings.
cc/min = lb/hr × 10.5Updated: July 2026
400 HP × 0.65 BSFC = 260 lb/hr fuel. Four injectors at 85% duty: 76.5 lb/hr each ≈ 804 cc/min. Round up to 850 cc injectors.
300 HP × 0.50 BSFC = 150 lb/hr. Eight injectors at 80% duty: 23.4 lb/hr each ≈ 246 cc/min. Stock 24 lb/hr (252 cc) injectors are adequate.
Higher BSFC (~0.70) for methanol enrichment: 600 × 0.70 = 420 lb/hr. Six injectors at 85%: 82 lb/hr ≈ 860 cc/min each. Consider dual injector setup.
Always target 80–85% max duty cycle. At 100% duty, injectors are fully open with no reserve for fuel pressure drop, heat soak, or unexpected boost.
Turbo engines run richer mixtures under boost. Use BSFC 0.55–0.65 for forced induction, not 0.45–0.50. Undersized injectors cause dangerous lean conditions at peak boost.
Undersized injectors lean out the engine at high power; oversized injectors cause poor idle and tuning difficulty. This calculator sizes injectors in cc/min from target horsepower, brake specific fuel consumption (BSFC), and maximum duty cycle.