Injector Scaling Calculator: Rescale Your ECU Injector Value After an Injector Swap
Injector Scaling Calculator
Fitting bigger injectors changes how much fuel your ECU delivers for the same pulse width. This calculator rescales your ECU injector value from the old injector to the new one and normalises for any difference in rating pressure. It also asks how your ECU stores injector size, so the value always moves the right way.
Sizing a build from scratch? Use the fuel injector sizing calculator first, then how to choose injectors.
Injector & ECU Details
ECU Platform
This ECU: bigger injector, bigger value
Old Injector (Currently Tuned)
43.5 psi
New Injector (Fitting Now)
43.5 psi
Current ECU Value
Value currently set for the old injector
Informational. Affects effective flow only
This tool estimates a scaling value only. It does not replace a wideband, professional calibration, or manufacturer data. You are responsible for verifying fuelling at idle and light load before any high-load testing. Incorrect fuelling can cause engine damage. TIRES + TERRAIN accepts no liability for loss, damage, or injury from use of this tool.
Quick Guide
Rated flow and pressure
Use the manufacturer figure and the pressure it was measured at, often 3.0 bar (43.5 psi).
Scale type
Flow rate values rise with a bigger injector. Fuel constants fall. Getting this backwards runs the engine lean.
After you apply it
Recheck dead time, then verify lambda on a wideband at idle and part throttle before load.
cc/min to lb/hr Reference
| cc/min | lb/hr |
|---|---|
| 160 | 15 |
| 260 | 25 |
| 370 | 35 |
| 525 | 50 |
| 630 | 60 |
| 840 | 80 |
| 1050 | 100 |
| 1260 | 120 |
| 1575 | 150 |
| 2100 | 200 |
Petrol, 1 lb/hr is about 10.5 cc/min
Injector Scaling FAQs
Do I scale the injector value up or down for bigger injectors?
It depends on how your ECU stores injector size. If it holds a flow rate or slope, as most standalones do (Haltech, Link, MoTeC), a bigger injector means a bigger number. If it holds a fuel-mass constant such as Bosch KRKTE, a bigger injector means a smaller number. This calculator asks which convention your ECU uses, because scaling the wrong way makes the engine run lean.
Does base fuel rail pressure change the injector scale?
With a manifold-referenced regulator the differential pressure across the injector stays constant, so both the old and new injector scale by the same factor and rail pressure cancels out of the scaling ratio. It still affects the effective flow figures the tool reports, which is why it is included as an informational input rather than a driver of the result.
How does injector flow change with fuel pressure?
Injector flow scales with the square root of the pressure difference across the injector. Doubling the differential pressure increases flow by about 41 percent, not 100 percent. That is why an injector rated at 3.0 bar flows more when the rail runs higher, and why ratings measured at different pressures must be normalised before they can be compared.
Does injector scaling set dead time and short-pulse adders?
No. Scaling only corrects the flow multiplier. Bigger injectors almost always have different dead time (opening latency) and small-pulse behaviour, so you must load those values from the new injector datasheet and verify idle fuelling on a wideband before any load testing.