What fuel should I burn in my E350 Mercedes benz

One of the few engines I recommend Premium grade high octane fuel for THE only factor NECESSITATING high octane fuel is compression ration 12.21 IS HIGH,SIMPLE..No. of cylinders V6 Displacement (cc) 3499 Bore (mm) 92.9 Stroke (mm) 86 Compression ratio: 12.2:1 Output (kW at rpm) 225 at 6500 Torque (Nm at rpm) 370 from 3500-5250

Shell, 93 octane

I have had E-350, E-550 and several SL550's. Each one runs great on Mid-Grade fuel (89 Octane). However, I do use Shell gas (if available) but not exclusively. On the 550 engines you might see a little more pep from the 91 Octane but not really noticeable. I have not experienced any noticeable fuel mileage difference between 89 and 91 Octane. Note: some areas have 93 Octane. As in any precision engine - Tier 1 fuel should be your first choice. I tried 87 Octane on my C-350 just to experiment. It was okay, but there seemed to be a difference in performance and mpg. In theory, as long as the engine does not ping - you can use and octane level - (87 or 89). However, good quality 89 Octane is a good blend of performance and keeping fuel costs down.