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Speedo Error 

All Gen 3 SHOs get their info from the ABS module (below from Helms)



The speedometer operates in the following manner:

The speedometer (17255) receives a speed/distance signal from the transaxle-mounted vehicle speed sensor (VSS) (9E731) (except 3.4L SHO).

* On SHO vehicles the speed/distance signal is provided by the anti-lock brake control module (2B373).

Speedometer displays speed in km/h and MPH.

The speedometer for 3.4L SHO is limited to 240 Km/h (150 mph).


I calculate

1st 6.94 mph / 1k RPM
2nd 12.57 mph / 1k RPM
3rd 19.23 mph / 1k RPM
OD 27.72 mph / 1k RPM

I remember 7, 12.5, 20, 28 for my mental calc when I drive down the road, that is close enough.

My speedo is 130/127 ~ 2.36% high. using Auto Tap to get direct OBDII readings.

For most SHO owners if their speedo is like mine it will read 2.36% high.

My summer tires are only 25.2" tall, which makes them 1.62% shy of OE.

.9838 x 1.0236 ~ 1.007 so the two errors off set to a large degree and my speedo is more accurate with 235/45-17's than the factory tire. It is with in less than 1%.

My 144 may have been 142.9934 MPH. since I don't know how to do decimals in Roman numerals I'll keep CXLIV ;-)




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