SpeedNeeds Tool

Fuel Injector Size Calculator

Pick a mode, punch in your numbers, then hit Calculate. Load Example only fills fields and never auto-runs.

Target Power (HP)

BSFC (lb/hp·hr)

Number of Injectors

Max Duty Cycle (%)

Weekend-warrior safe zone is usually ≤ 80%. Over 85% is living on the edge.

Your Base Fuel Pressure (psi)

Reference Rating Pressure (psi)

Fuel

Fuel Density (g/ml)

Results

Duty ceiling: —

Per-Injector Size @ Base

—

— cc/min

Rated Size (reference)

—

— cc/min @ 43.5 psi

What this is doing (formulas)

Required per-injector flow (lb/hr) = HP x BSFC / (Injectors x Duty)
cc/min = (lb/hr x 453.59237 / 60) / (density g/ml)
Pressure scaling: Flow2 = Flow1 x sqrt(DeltaP2 / DeltaP1)

Typical BSFC: NA gasoline ~0.45-0.55; boosted ~0.60-0.75. E85 often needs ~25-35% more fuel mass (higher BSFC).