With nitro motors, you normally have a couple sizes for sport hydro. Sport 20 ( maybe 30” long or so) and sport 40 (usually around 36”). You’d be looking for a .21 size motor for sport 20 and up to .46 for sport 40. Find out more about your kit and get the right size motor. There are not many manufacturers of new nitro motors out there other than CMB that are readily available. Plenty of used stuff though. You also have Gasoline powered motors for larger sport hydros. These are similar to the motors on a weed whacker. These boats are typically 48” and up. If you have a club locally, join it. This normally comes with access to a lake and lots of hands on knowledge.