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[2woody]

40% ! that's ahuge margin. The last one I was involved in for a manufacturer had 4% and even then we thought that was too much

[Kevin Wood]

The Omega seems to allow about 20% fuel trim before it gets upset and lights the EML. But that's not what we're talking about here. Fuel trim is a correction of the fuelling against what is calculated for the current mass air flow, under light to medium engine load.

Put a bigger engine in and the mass air flow at wide open throttle increases; hence the calculated fuel requirement increases, and it'll be roughly correct for the engine so no need to increase fuel trim (it'll actually be running open-loop by then anyway, so the ECU won't know if the fuelling is right). Granted, at some level the ECU will regard the MAF reading as not plausible but the question is where that threshold is set.

[cem_devecioglu]

at least we know with a bigger engine and full throttle we are in the twilight zone