Speedometer and Differential Ratios

[HB Chris]

The e9 coupes came with three differential ratios and could be found both open or unlocked and locked or LSD. The speedometers were matched to the car based on which differential was fitted.

Differentials

The differential ratio is expressed as a fraction and is stamped on the right lower side of the differential on a flat boss. The presence of a stamped or painted S indicates locked or LSD.

3.25 = 39/12
3.45 = 38/11
3.64 = 40/11

These differentials were typically found on these models:

3.25 Open - CSi
3.25 LSD 25% locking - CSi and CSil
3.45 Open - Euro 3.0CS/CSA
3.45 LSD 25% locking - CSL, Euro 2800CS/CSA and 3.0CS/CSA and US 2800CS/CSA
3.45 LSD 40% locking - Euro 2800CS/CSA and US 2800CS/CSA
3.64 Open - Euro 2.5CS/CSA and US 3.0CS/CSA
3.64 LSD 25% locking - 2.5 CS/CSA

The LSD could be ordered as an option as well.

Speedometers

The speedometer ratios are as follows (numbers stamped on the speedometer are rounded and include a mm/yy build date):

3.25 KPH W= 0.679
3.25 MPH W= 1.078
3.45 KPH W= 0.7125
3.45 MPH W= 1.14
3.64 MPH W = 1.2164

Note: MPH includes not only the US market, e.g. the 3.25 MPH speedometer

3.45 Locking differential identified by the stamped S

Internal S 25, sometimes visible through the vent hole

 

[rsporsche]

for those interested in the speeds of a given diff ratio with the getrag 265 (5 speed) see the charts below. as i understand, the 262 (4 speed), the gearing is the same for the first 4 gears.

 

[HB Chris]

Perfect. Users should note that this is with 16” wheels/tires but should be very close. The numbers match my experience.

 

[Markos]

Love the activity in the FAQ! The dogleg pattern is below if anyone is up for generating more PDF's. I can always do it later.

Ratios for the G265/5:

1. 3.72
2. 2.40
3. 1.77
4. 1.24
5. 1.00

 

[rsporsche]

okay, here are the speeds / rpm for the CR dogleg box. the combination of a CR box and the 3.25 diff looks intriguing ... but i am happy with the 3.45 and the standard 5 speed.
@HB Chris i checked with the 16" tires and the 195/70-14 tires ... and the numbers were basically the same at 3000 rpm

 

[rsporsche]

here are a couple of other charts with different rear tire sizes - all with the 3.45 diff. 205/70-14 ... 215/60-15 and 225/45-17. all are basically the same but its worth seeing