# Fuel: Fuel Injector Size Adjustment Calculations

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Fuel Injector % Adjustment Calculation:

This is how to calculate the base fuel injector size base correction factor for any Piggyback fuel controllers like a Super AFC, MAFT Pro, Emanage.....

This Formula calculates the amount the Fuel controller needs to decrease the airflow signal to the ECU to adjust for bigger Injectors:

(Stock injectors/Current injectors - 1 ) * 100% = adjustment %

For Example: If you have a TT with 360CC injectors stock and you switch to 580cc

• 360/580 = .62
• .62 - 1 = -.38
• -.38 * 100% = -38%

Some common TT injector swaps:

• 360 to 450cc = -20%
• 360 to 510cc = -29%
• 360 to 550cc = -35%
• 360 to 560cc = -36%
• 360 to 580cc = -38%
• 360 to 660cc = -45%
• 360 to 720cc = -50%

Some common NA injector swaps:

• 210 to 240cc = -13%
• 210 to 360cc = -42%
• 210 to 450cc = -53%
• 210 to 510cc = -59%
• 210 to 550cc = -62%
• 210 to 560cc = -63%
• 210 to 580cc = -64%
• 210 to 660cc = -68%
• 210 to 720cc = -71%

Most Piggyback fuel controllers can't adjust more than -50%. Even if the fuel controller can adjust more than -50% the ECU will see so little airflow that it will eith adjvance the timing too much or get so far off the normal fuel map that the car is impossible to tune. If the fuel controller can only adjust to 50% but the injectors require a little more correct (like 53%) the stock ECU trims might be able to adjust enough to make it work.

• The biggest practical injector upgade for NA ECU is 450cc (-53%)
• The biggest practical injector upgrade for a TT ECU is 720cc (-50%)

This is why most NA cars doing a TT conversion switch to a TT ECU, so they car run larger injectors.