It does seem to be backwards. The higher the Octane the less Volatile. The lower the Octane the easier it is to ignite it. One natuarly thinks the higher the number the more power one would get. That is not what it is all about....................

I think this is the concept behind deisl engines. It ignites under compression hence no spark plugs.

The engine will retard the timing if the engine knocks/pre-ignition. The problem with that running your car with the timing retarded is you are running your car in a non-optimal mode. You will loose power, gas mileage etc. The money you potentialy save on the lower octane gas would be lost.

Also the ECU can only retard the timing so much and that is where you run the risk of piston melt down.. I have no idea what those limits are.

I have a 91 300E(SOHC 16V) and the manual says 91 Octane or higher. In my area my gas choices are 87, 89, 90 or 92 Octane. I use 90 Octane to be on the safe side and havn't had any pinging, knocking etc..

I have a Haynes manual (European Version?) and it actual shows an item next to the ECU that allows you to adjust the timing so one could use lower Octane fuel.. This item (sorry I don't have the name of it) doesn't exist in my car. I asked the MB dealer/Mech and they commented that it must only be in the Euro Models because they never seen such an Item..