Cam duration is a big determining factor in the operating range of a motor. A small duration number favors low rpm operation, while bigger numbers favor high rpm. Above all, the components must be well matched. A big cam may not make the power you want if it is matched with a stock
carburetor or small valve head. Duration is often measured at .050 lift (50 thousandths of an inch) this may give a more accurate idea of the camshaft nature when compared to other .050 duration numbers. Some cams have opening rates that are very slow, and can make it look like a big duration cam, when it really isn't.. 050 figures allow the valve to open a bit, and provide a better comparison between cams. All that said, Nelson Racing makes a really good mini
bike cam- the 280 series. It has high lift, and short duration. Duration is 220 at .050, lift is .280. It is advertised as the ultimate mini bike cam. It would replace a stock cam, and work with the other stock components. I had one in my built predator, and it ran great. I switched to the black mamba cam which is 245 at .050, and .275 lift. It moved the powerband up to the 4000- 7000 rpm range. Iirc, the NR cam started pulling about 2500, and ran out of suds about 6k. If you can make the same power at a lower rpm, it is much easier on parts. The go cart racing folks have really figured the predator motors out, but with all the rules, it can be hard to find something suitable for a no-rules mini
bike. The NR cam is a really good one, imho.