Polaris Engine History

I am trying to remember some engine history and wondered if anyone could tell me what years had what engine. Of course, this year we have the 850 Patriot. In recent years Polaris introduced a new engine with a lightweight crankshaft, 3 stage exhaust valves, electronic oil pump, some sort of integrated mount, and side grooves in the pistons. What model year of sleds had these changes? What engine does the MY16, 17, and 18 have? P.S. I'm talking about the mountain sleds. Pro RMK, AXYS RMK, etc.

Thanks