A 600cc dirt bike may go as fast as 120 or more miles per hour. Dirt bikes are generally geared a little lower than street bikes, so the top end would be a little less.
how fast does 250cc Orion dirt bike go
fast enough
210
about 60mph
56mph
100
about 60mph
about 40mph
140cc
it all dipends on the bike
A 70cc dirt bike will achieve a top speed of around 40mph
not very fast