370z Auto - High-RPM acceleration issue w/ 3.7 gears

filip00

Going on a wild guess here, but is it possible that the auto ECU must be recalibrated, since it thinks the car is going slower/faster than it should? I'm guessing it's configured to have the basic calculation of car speed from the gear*diff*wheel size, whereas now the diff ratio is changed and the redline isn't where the car thinks it is, and the shift aren't happening when they should happen.

jmikes

The speedometer is in fact off by about 5% after the diff swap so that is a possibility. 5% is also about the amount past 7200 that is slow to rev.

However I haven't been able to get the speed calibrated properly through HPTuners. There is a speedometer calibration setting but it has zero effect on anything.

I figured it could be something to do with that, but I wouldn't think that the speed reading being off would make the ECU start acting up at high rev's when the majority of the tables are based on engine RPM and not your speed.

If this is the case, is there any way to properly calibrate it through the ECU or do I need to replace something physical in my swapped diff?

Edit: I should also mention that my car is a 2017 but I got either a 2009 or 2010 MT diff. Was there a manufacturing difference between those years that throws off newer ECU's? I know that the older diffs had completely different axle stubs, which I have appropriately obtained and installed already.

Edit 2: I'm dumb, forgot my speedo didn't change until I changed my wheel and tire setup a couple months after the diff change. Wouldn't even make sense for it to do so, so it isn't anything to do with the speed readouts.

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2017 370z 7AT (Metallic Black)
Stillen / ISR / PowerTrix / Morimoto / DAR / Enkei / Akebono / DBA / Michelin