Use whatever fuel grade/octane that does not cause your engine to PING under a load. In my 1995 SL320 with a M104 engine I have been using 87 octane with no problems for 6 years. In my 86 M103 engine it will only take 91 octane , so go figure

__________________
Jerry

2004 SL500 Black 55K Miles
2002 s500 Black 90K Miles
1986 300E Gold 233K Miles
1966 Twin Cessna 320D
1989 Jeep Cherokee 233K Miles
1994 Ford Van E150 399K Miles