Page title says it's a drag racer, so I took the liberty of making the following guesses:
- Engines aren't running long enough to overheat
- In the Swiss-cheese excavator bucket-looking cover is what I'm guessing is a clutch. It very well may be the case that this gets run wide open throttle and acceleration and speed are modulated with the clutch.
All of this is just guessing. I have no first-hand experience with drag racing drivetrains, motorcycle or otherwise. I do seem to recall learning that there are automotive drag racing transmissions in which the clutches weld themselves closed during the race and need to be rebuilt between runs.