I've never heard any detonation sound (of course it is a pretty quiet engine). I use premium gasoline anyway, my owner's manual recommends it. It's a small price to pay for a good boost in power and mileage. I've never seen the cars overheat either, except when my radiator got blocked once. I guess I should feel guilty about the nitrogen oxides, but this car uses so little fuel that I expect the emmissions are still minor.

Having run one of my cars for over 100,000 miles with that timing, I don't worry too much about damaging the engine, but I'll keep it in mind. Thanks for the advice.