e34 M5's: What's the diff between the

[Jon K]

Europe has the same octane fuel as the US they just go on a "RON" system version our motor octane. 98 there is 93 here. 95 there is 89 here... and so on.

[Brandon J]

That's correct. US e34 M5s were tuned for 91 octane, not 93. I get 93 here in Chicago so I can use the euro version chips based on 93 octane.

Europe has the same octane fuel as the US they just go on a "RON" system version our motor octane. 98 there is 93 here. 95 there is 89 here... and so on.

[ILoveMPower]

From some gurus over at m5board:

At some point in 1990, BMW altered the final drive to 3,73:1 for the HD93 (US) model. Until then, BMW used a final drive with 3,91:1 ratio for all models (HD91, HD92 and HD93). The reason for that was to lower the engine speed under normal driving conditions. The HD91 and HD92 and later the HC91/HJ91 and HC92 models kept the 3,91:1 differential until 4/94 when 1995 model with six speed gearbox came onto the market. I also believe that the HD93 variant has OBD whereas the HD91 and HD92 variants do not. Last but not least, the HD93 variant was manufactured alongside the HC91 and HC92 models during 1992 for the 1993 model year and the last S38B36 engines received some improvements from the S38B38 such as a throttle position sensor in stead of a throttle position switch.

the 92 model year (typically, around 9/91 production) is when bmw NA started getting the 3.73 gearing. 91 model year was 3.91 here.