What car??
ON a 1988 190E 2.3 timing cannot be adjusted!

Higher octane fuel doesn't make for better running or more power unless the engine was designed for it!
The 1988 190E 2.3 has 9/1 compression & should run on 90-91 octane.

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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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