how do I know if I over revved

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Gentle suggestion: Avoid downshift over rev. That is the one of the best ways I know to score main bearings and induce rod knock.

When practicing heel/toe, shoot for 4k rpm rev match downshifts which is straight up on the tach. Porsche designed it this way so it could be seen easily with peripheral vision. 4k is usually pretty close to the sweet spot for acceleration through the next gear and if you target 4k, you may see 5k in the heat of battle, but not 7k with connecting rods sticking out of awkward places. Your motor will thank you with a long happy life.