Injector Duty Cycle Calculator
Reverse injector math — from current injector size and target HP, compute duty cycle at peak.
How to Use
- Enter injector size (lb/hr or cc/min), count, fuel BSFC, and HP target.
- Tool returns duty cycle — watch for the 85% danger zone.
Injector + target
Duty & headroom
Formula
Duty
duty% = (HP · BSFC) / (N · lb/hr) · 100
Max HP
HP_max = (N · lb/hr · 0.85) / BSFC
Frequently Asked Questions
When is duty too high?
> 85% static = pintle barely closes. Lean spike under boost, heat stress, and tuning becomes glitchy.
I'm at 95% — what now?
Upsize injectors. "Fixing" via rail pressure past 75-80 psi stresses pump and injector coil.
Dead time matters?
Yes — real duty adds ~1 ms per event of latency. At 6000 RPM that is ~20% of the window.
Common Use Cases
Dyno sanity check
Confirm injectors have headroom before pushing more boost.
Logging review
Compare calculated vs logged duty to catch discrepancies.
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