Do I have to rescale the tune when changing injector size?
Yes. The computer calculates fuel from the injector data you give it, so new injectors need new data.
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- Flow rate is the foundation of the fuel calculation. If it's wrong, the engine never runs right, or the error hides a mechanical problem. Injector setup is among the first steps of any tune.
- Enter the full characterization, not just flow. In one 1,000cc injector swap, the tuner entered the supplied flow rate, offset (dead time) and short-pulse adder data.
- Match the fuel pressure. Injectors are rated at a set pressure, commonly 43.5 psi (3 bar) or 58 psi (4 bar), and flow scales with the square root of the pressure difference. Set the fuel-pressure reference correctly (atmospheric vs manifold-referenced), because flow and dead time both change with differential pressure.
- Use characterized injectors. Fully characterized injectors let the tuner get idle and drivability right.
Want to do it yourself? See who tunes it, and how to learn.
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Verify the injector change
Confirm the new characterization with logs: fuel trims and wideband readings at idle, cruise and wide-open throttle. Use a safe closed course for load testing.