The hedgehog engine is created by sega and it is a graphics engine that has global illumination and it has havok 5 physics engine with it so it's both.
Graphics engine of course means graphics. Game engine however might mean how the game runs. That or you mean Source engine where you can download the game onto another game.
Engine Revolutions Per Minute (RPM) can be "safe" at a variety of levels......depending entirely on what the vehicle is doing. On the HIGH end: If the question is meant to determine "how fast can my...