[asphaltgambler]

Some of the problems with the older EVO / single cam design was the awful valve train geometry especially on the front exhaust pushrod / rocker set-up. As soon as you start adding camshaft lift / duration and then, or course, added spring seat pressures - valve train noise and stress go up exponentially. My lest EVO 117" street engine was total bad@ss but when hot and idling at a stop light it emitted sounds from the rocker covers like someone had thrown in a handful of gravel inside.

Also while the EVO was a good step forward from the extremely outdated / long past due retirement Shovel, it lacked structural strength and too many gasketed 'things' to move around and leak oil when really pushed to make HP/TQ.

The Twin cam design was / is a huge step forward by eliminating a lot of bolt-together-things like casting the cases and lifter blocks as one piece, adding material in the deck and crank bearing area. Star-Racing / S&S then further engineered their own engine based on the already proven piece.

BTW, HD already knew this even as their first twin engines were in production in the late teens / early twenties. For their racing engines (board track)they did a twin-cam version that was very proved very successful. Unfortunately, it proved to costly too manufacture in 'street' engines at that time.