86-89 will be at 2,800 rpm at 60mph. About 3,500 rpm at 80 mph. 89 was same at cruise, same overall axle, just different 1 and 2 gears. 90-92 will be slightly less. As I recall about 3,300 rpm at 80 mph. About 2,400 rpm at 60. It was minor at highway speed. These engines aren't really "noisy," per say.

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1988 Mercedes-Benz 260E