I'm sure this question has been beaten to death in some form or other. It's my turn to get a couple kicks in...

I got a wild hair and decided today would be as good as any other to get a new engine for my trug. I'm looking at the Novarossi 528 engines. I had assumed that the Nova, Rex, and Top engines were all made by Novarossi, and that they were all identical. Looking at the specs on the Nova site, I couldn't help but to notice that the Novarossi and the Rex engine is basically the same engine on paper. The Top however, seems different. Max power on the Nova and Rex is 2.87hp @ 34000RPM while the Top is 2.85hp @ 33500. Whether the Top will make 2.87 at 34000 is unknown to me. The prices are a bit different also. Sooo, would somebody care to tell me whey they market 3 engines that are identical and what’s different?