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Calculator · Fuel pressureInjector flow rate at a different fuel pressure
An injector rating is only true at one pressure. Raise the rail pressure and the same injector flows more; drop it and it flows less — but never in direct proportion. Flow follows the square root of the pressure change, and this calculator does that maths for you in psi or bar.
Most injectors are rated at 43.5 psi, which is 3 bar. 58 psi is 4 bar — a common adjustable-regulator setting.
The formula
New flow = rated flow × √(new pressure ÷ rated pressure)
Flow through a fixed orifice grows with the square root of the pressure pushing through it. Doubling pressure does not double flow — it multiplies it by about 1.41. That is why a modest pressure bump is a cheap way to gain a little headroom, and why it can never rescue a badly undersized injector.
Worked example (pre-filled above): a 320 cc/min injector rated at 43.5 psi, run at 58 psi: 320 × √(58 ÷ 43.5) = 320 × 1.155 = 369.5 cc/min (35.2 lb/hr). A 15.5% flow gain for a 33% pressure increase — the square root in action.
Practical limits
- The pump must hold the pressure at full flow. A regulator setting means nothing if the pump cannot deliver the volume — check it with the fuel pump flow calculator.
- Very high pressure hurts spray quality and can stop some injectors opening cleanly, especially at idle pulse widths.
- The ECU must know. If you change pressure, the tune has to be told the new effective flow, or fuelling will be off everywhere by the same factor shown here.
Flow is only half the story
A partially clogged micro basket filter cuts real-world flow no matter what the math says. The Micro-Filter Basket Removal Tool, from $14.99, pulls the old ~6 mm basket filter straight out so a fresh one can go in — see the step-by-step removal guide. For a full service, the Universal EV1 Rebuild Kit, $72.49 covers 200 injectors with filters, seals and caps.
Free tracked USPS shipping in the US · 30-day returns · secure card checkout by Stripe · sold by Partsapiens.
More injector calculators
- Injector flow converter — cc/min ↔ lb/hr.
- Injector size calculator — injector size for a target horsepower.
- Max horsepower from your injectors — the reverse calculation.
- Flow rate at a different fuel pressure — the square-root rule.
- Injector duty cycle calculator — pulse width and RPM to duty %.
- Fuel pump flow requirement — LPH your engine actually needs.
Last updated October 20, 2026 · Partsapiens, 5325 Alton Pkwy, Suite C300, Irvine, CA 92604 · partsapiens@gmail.com