Turbo muffler explosion:

Go on any course with a car you can put a turbo in (best with an Evo). Get up to top speed or just drive very fast. Suddenly release the gas or hit the brakes. You will hear the turbo letting air out. Then, an explosion will come out of the muffler. This is a nice effect for editing replays.
Tamiya Kagegawa circuit:

Complete the "Final" level (seven races without the mountain passes). There is a Strict Remote Controlled car challenge. Note: Your car will not be as fast as they would on an ordinary track. The speed is in MHz.