It'll improve accelerating but it might reduce top speed a little.
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.
depends if the sprocket is bigger or smaller than a stock sprocket.
43/16
15-36 is the best
13t front 40t rear
The chain is size 530, and the stock gearing is 15/45, meaning that the front sprocket has 15 teeth and the rear sprocket has 45 teeth.
I run a stock rear sprocket and 15 front. does great for 500 ft drags
They came stock with a 49T or 48T rear sprocket you can choose a replacement with either a 48T, 49T, 50T, or 51T, if you have the old sprocket count the teeth on the sprocket and that tells if it is a 48T, 49T or whatever (48T = 48 teeth)
45 tooth rear
I think 17/42 is stock
12 counter sprocket 47 rear
14t on front. 40t on back