Injector Change Fuel Table Calculator

Changing injectors on an existing injection-time fuel map? Compare old and new injector flow to estimate the fuel-table multiplier and percentage adjustment needed to deliver the same fuel quantity.

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Flow entry

Flow units (both setups)

Old total flow

New total flow

Existing injection-time table value (ms, optional)

Use actual flow at each setup’s operating differential fuel pressure, with the same fuel and units. Total-flow mode already includes all injectors in the bank—do not multiply again. Changing units relabels the entries; enter matching values for the selected units.

Estimated fuel-table adjustment

Multiply existing values by

Two injector banks → one bank (8 injectors → 4)

Enter flow per injector and injector counts. This example combines four 24 lb/hr primaries and four 62 lb/hr secondaries into four 100 lb/hr injectors.

Old primary flow per injector (lb/hr)

Old primary injector count

Old secondary flow per injector (lb/hr)

Old secondary injector count

New flow per injector (lb/hr)

New injector count

The capacity ratio assumes equal effective opening time for both old banks. Staged banks may use different injection times. Use the cell-by-cell calculation below where secondary contribution changes; a single percentage will not reproduce the whole map.

Calculate one matching RPM/load cell

Enter each old bank’s effective injection time excluding dead time. Enter 0 for the secondary when it is off. Values must represent the same engine cycle and injection-event count; if event counts differ, use the sum of effective opening times per cycle for each bank and configure the new event count separately.

Old primary effective time (ms)

Old secondary effective time (ms)

New effective time = [(primary flow × count × primary effective time) + (secondary flow × count × secondary effective time)] ÷ (new flow × count).

The result excludes new injector dead time. Configure the new injectors’ characterization in the ECU; only add dead time to the displayed value if your table convention includes it. Use actual flow at each setup’s operating differential pressure with the same fuel. Save the original map, reconfigure staging for the single bank, and verify lambda/AFR. This preserves estimated fuel quantity for the injector change only; engine, fuel, or nitrous changes need separate tuning.

Single-bank math

Multiplier = old total flow ÷ new total flow
Percentage change = (multiplier − 1) × 100
New injection-time table value ≈ old value × multiplier

Example: 96 ÷ 248 = 0.387097. Keep 38.71% of the original table value, which is a 61.29% reduction. A 10.00 ms value becomes approximately 3.8710 ms.

Use as a starting estimate for an injection-time map. Check your ECU’s table mode and injector configuration first. Do not apply this multiplier to a VE or fuel-mass/flow table that already compensates for injector flow. This simple ratio does not account for injector dead time, short-pulse nonlinearity, or minimum pulse width. Update injector characterization and verify lambda/AFR with your tuner before operating under load. Save the original map first. For two banks being combined into one, use the two-bank section above and calculate each affected RPM/load cell. Injector staging must be reconfigured separately in the ECU.