[Isaac Zachary]

10.7:1 still doesn't mean it needs premium in my opinion. I don't try to second guess manufacturers and their recommendations. So many other things affect detonation that the compression ratio is meaningless without taking every other part of the engine design into account.

For an example, one thing I did on my Bug was create a .030" piston to head "quench" space which lowers the chances for detonation, which is why some call it "mechanical octane." Modern engines have an even tighter quench and that is even slightly wedged to maximize its effect. Another factor is fuel atomization and head designs that keep the fuel atomized also greatly reduce detonation. 10:1 is high CR for a carbureted car. It isn't for a modern fuel injected one. Then there's also the cam profile factor. Many modern fuel-efficient engines create an atkinson cycle effect with their cam profiles. As a result, the actual dynamic compression ratio can be far lower than the measured static compression ratio.

At any rate, if it's only 10 cents more expensive, then by all means do what you want to do. Premium is 90 cents more expensive here. That's almost a dollar more per gallon, or nearly a third more expensive. It is even a pain to have to pay more for our mid-grade, which is 87 octane or regular everywhere else, every time I have to drive out of state. I can nearly reach the coast on one tank and wouldn't want to do it with 81 to 85 octane.