Butt-O-Meter

[CanAutM3]

Originally Posted by catpat8000

Didn't they do this with the E9x also?

You could look at my E90 tach using a microscope and you'd see the redline was 8250 rpm. The DCT in S6 shifted at 8250 rpm but BMW insists it has an 8400 rpm redline. I still don't believe it.

Yes, you are right, the E9X shows a 8250 redline. The tachometer in the E9X M3 seems to have been borrowed straight from the E60 M5 that actually had a 8250RPM redline.

I never got the final story on that one. But it seems that the tacho on the E9X M3 does not indicate the true engine speed. When accessing the hidden menu in the instrument cluster, you can have the RPM digitaly displayed and there seems to be a ~2% discrepancy with the analog tachometer. So 8250 on the tacho is really 8400.

[catpat8000]

Originally Posted by CanAutM3

I never got the final story on that one. But it seems that the tacho on the E9X M3 does not indicate the true engine speed. When accessing the hidden menu in the instrument cluster, you can have the RPM digitaly displayed and there seems to be a ~2% discrepancy with the analog tachometer. So 8250 on the tacho is really 8400.

That probably explains why I would see the DCT in D5 shift from 1 to 2 well below redline - often around ~7500 rpm. The tach probably lags true engine speed. But I don't think it's probable that this lag is a constant 2%. It might be 2% on the 2-3 shift. More likely the tach lag is correlated with the rate of increase of engine rpm. Does that mean the F80 M3 will have two types of lag? Turbo lag and Tach lag?

Someone needs to do a 3-4 shift at full throttle in D5 DCT mode and report on the rpm.

[CanAutM3]

Originally Posted by catpat8000

That probably explains why I would see the DCT in D5 shift from 1 to 2 well below redline - often around ~7500 rpm. The tach probably lags true engine speed. But I don't think it's probable that this lag is a constant 2%. It might be 2% on the 2-3 shift. More likely the tach lag is correlated with the rate of increase of engine rpm. Does that mean the F80 M3 will have two types of lag? Turbo lag and Tach lag?

Someone needs to do a 3-4 shift at full throttle in D5 DCT mode and report on the rpm.

You bring a good point about lag on the tacho. There might be a damper on the readout, so the faster the RPM changes the greater the lag.

But this not what I am talking about, what I observed is an actual ~1.8% error in steady state. A few years back, I drove the car on the highway in 2nd gear and adjusted the cruise control until I got 8000RPM on the analog tacho. The digital readout of the hidden menu was showing ~8150RPM. I did the same in 3rd gear at 6000RPM and the digital readout was ~6100RPM.

In another thread, Mike Benvo seemed to beleive that the analog tacho is actually showing the true RPM (and I trust Mike), but it is not in line with my observations. This is why I am saying I never got the final word on this story, I might need to repeat my test .