depends if the sprocket is bigger or smaller than a stock sprocket.
I have a 2006 400ex With a k@n airfilter fmf power core 4 exhaust and a dyno jet kit I get 76 out of it
my 400 ex will go 175km on a gravel road
With standard sprocket and wheels not over 95 km/h.
55 mph and over 60 mph with a sprocket change.
55mph average but 60pmh is easily obtained with a sprocket change
63. If you have a 2007 like I do I clocked it against a 2006 Ford mustang gt and got 73 mph also my 2006 Honda trx250 goes 60
A stock Honda crf450r will hit about 90-95 mph.But it all depends on the weight of the rider and what your tooth ratio is on your sprocket's? If you have a small sprocket on the front and a big sprocket on the back you are going to get more top end speed than acceleration .if it is the opposite way around you are going to get more acceleration but less top end speed.
75MPH Stock, 80MPH With 15 Tooth Front Sprocket exhaust, intake and jetting.
about 63 mph
around 67
65 to 70 if well maintaned and aftermarket parts Don't listen to this guy, bone stock 75 miles an hour. My cousin's a cop and we used her radar gun one day down at the farm with my 300ex and it did 67mph, the only diff is I'm running on different gear ratio.
stock 70mph. Put a larger 14 tooth sprocket on the front and you can re gear it to it 80mph.