What happens when your engine is driven beyond the redline?
The higher you rev an engine, the more stress it will suffer. If you rev it beyond the redline, it may have a serious faliure. Luckily almost all cars have electronic rev limiters that restrict the RPM once it reaches a certain stage by cutting off the fuel until the RPM falls again. This is the real point where exceeding it will cause severe damage. In high performance cars, the redline tends to be the optimal shift point rather than the maximum RPM - exceeding it will make you slower rather than faster.
However, it is possible to over-rev an engine in a manual-transmission car by going down a hill quickly and shifting into 1st gear. This could cause overheating or parts breaking (especially the pistons - they will undergo huge acceleration).
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