Originally Posted by paulv
I'm staying out of this thread -- you guys are way over my head! My mechanical abilities are still in diapers!!
Paul! You surprise me. I figured you for a blasting debate on this one!
In reality DBW is correct, assuming the engine is used to its full potential (60%+). Most drivers use less than 25% of their engines' rated output, so ... those that use lower power settings can get away with lower octane.
Mercedes, unlike Ford, Nissan and the rest are selling Horsepower to the uninformed consumer. They, like I did for 15 years, are pulling every possible pony out of every cubic inch. Face it, it's much more attractive to buy a sedan with 350hp than one with 120hp, bragging rights.
In reallity, so few people extract 100% of their engines rated power. How many of you have taken the tach to 5500 rpm and held it there at speeds of 150+ ? Speed limiters aside, I would guess none of you reading this have and if I am wrong, you felt uneasy about the possibility of a connecting rod flying through the hood.
I live in two mechanical worlds, auto and aircraft. Aircraft engines are designed to put out their rated power for hours on end, in some cases over 1000 hours. However, strict use of high octane high quality fuel is mandated ( Don't get your feathers ruffled DBW, I'm not refering to jets). Racing engines do the same but for much fewer hours. In some cases their outut can be measured in minutes. Once again, they depend on exotic, high octane fuels or they will blow apart at start up. Common characteristic, they cost thousands more and put out 100% of power BY DESIGN.
My 45 cents being said, if you drive hard you should use the higher octane fuel. If you drive at road speeds of 70mph+ for lengths of time, use higher octane fuels. If you drive in commuter traffic, park at the office and repeat the same at 5, you can "get away" with lower octane.
And no .. the E55 gets premium.