The most common way is gearing or a pipe.
The YZ is a motocross bike, the trail or woods bike is a WR426.
the speed depends on how well tuned the bike is and also the size of the engine.
If you want to know top speed, you should not be buying this bike. This is a motocross and not a drag bike.
A cr250 is a motocross bike
By dirt bike do you mean and enduro bike or a motocross bike or some other bike at all? For any bike except motocross bike you definitely need license, and for motocross bike you don't, because you can't ride it on the streets at all... You can only use it in motocross tracks and for that you need to have a special permit...
Become enthusiastic about motocross bikes.
If by bike you mean bicycle then: Yes if you increase your speed or the intensity for that matter then your heart rate will also increase.
2006.
a bmx bike
Dont.
A fast one.
Motocross was invented by edmann wilkison as a game to show off the dirt bike skills