in my opinion (and not that I have experience with either engine yet, but hopefully soon lol), the two best engines for a motorized bicycle are a morini or a predator, at least from what I hear. its not cheap to install either engine, but worth it from what I have read. I am not sure if there is a way to achieve good gear reduction on a morini with a single gear on the back, but i know it can be achieved fairly easily with the predator, and there are a few options available for a transmission. Thats why I am installing a predator on my cruiser as soon as I aquire the funds. I have a 44t rear sprocket, and with the transmission I am going to install, I am still going to be able to achieve proper reduction for a final drive of 8.96:1, which is double what you get with a china engine.