Redline

The piston acceleration is directly proportional to the magnitude of the G-forces experienced by the piston-connecting rod assembly.

As long as the G-forces acting on the piston-connecting rod assembly multiplied by their own mass is less than the compressive and tensile strengths of the materials they are constructed from and as long as it does not exceed the bearing load limits, the engine can safely turn without succumbing to physical or structural failure.

The Gordon Murray Automotive T.50 has the highest redline of a piston-engine road car rated at 12,100 rpm.

The Renesis in the Mazda RX-8 has the highest redline of a production wankel rotary-engine road car rated at 9000 rpm.

If manual override is used, the engine may go past redline for a brief amount of time before the ECU will cut power to pull it back or auto-upshift.

If a driver accidentally selects a lower gear when trying to shift up or selects a lower gear than intended while shifting down (as in a motorbike sequential manual transmission), the engine will be forced to rapidly rev-up to match the speed of the drivetrain.

This is known as diesel engine runaway, and can be stopped by blocking the air intake, or opening the decompression valve.