Hey Phil... If you read the manual on any Benz with a 3.0 or better engine 89 and above (89 is the last year I looked up) you will see that the compression ration is 9:1 and up... that is why you put premium (HIGHER OCTANE for those grammatically challenged) doesn’t have anything to do with price... I said cheap because there is a difference between having a low price and having cheap gas... there is a reason a SATURN is built to run 87 octane.
Just curious... is your friends’ race team built of Saturns? (OK I will give you props if you are using an old car with a low compression ration) but that will give you but only so much power (referring to the compression ration there, don’t go off on a tangent) why do you think that the fastest cars in the world (F1's) run? Pac West runs a Benz engine in their Champ Car... do you think it would even run on 87? Possibly, but I think there is a reason they use methanol. Do you think methanol doesn’t give you any more power? What about 103 octane... I can go get it down the street for about 4.25 per gallon... think that wont make a difference?

91 octane or above... there is a reason why this is in the manual.

With you being such a smart guy wouldn’t you think I would rather put 87 in my tank since it costs about 30 cents less per gallon than 93.