Nothing. The engine is designed to operate in the RPM range dictated by the ECU for safety, so unless you modify it and try to rev the engine HIGHER than it can safely handle (trying to upshift from 2nd to 3rd and hit 1st by accident, for example), it won't do anything to it. Might actually help, as it can help clean out carbon deposits, which is why it's actually good to drive your car hard once in a while, to keep all that broken up and keep the engine clean internally, which helps keep good gas mileage and reliability, as well as keeps the power up.
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