Most modern dirt bikes with a standard engine size of over 150cc have the capability to reach up to 60mph.
These dirt bikes have finely-developed and constructed engines that can cope with tough terrain and reach a top speed of around 50 – 60 MPH. Different factors such as terrain and ground conditions affect the speed of these vehicles.
This is the type of engine that can be found in a lot of dirt bikes. It's also known as 2-stroke or pinner engines and can be seen used in other motorcycles.
A lot of four-stroke dirt bike engines are also referred to as thumpers because they generate more power than 2strokes. Their design has two pistons and a much higher compression.
The top speed of a 150 CC dirt bike can also be affected by human factors. The height and build of the person riding, usage of the bike, and budget to purchase the bike play a role in what top speed you can achieve.
The engine performance has improved as a result of the performance exhaust. It allows for more power/gas usage and higher speed.