i would not suggest overfilling unless you are at the track (with no baffle). for a daily driver just keep it at the full mark and you'll be just fine. the problems occur when your tracking the car with stickier tires and pulling more G's in right handers! in a daily driver the extra oil will probably be above the windage tray hitting and slowing the crankshaft and getting sucked into the breather system and burned. When installing an oil pan baffle, it's sugested to use synthetic oil and add 1/2 quart above full mark. I don't have the baffle yet and I'd rather change good motor oil frequently than deal with leaks, but my question-is it harmful to over fill the oil by 1/3 to 1/2 qt?