Some of you might know that I am an engine performance specialist on RE bikes. I have built the performance parts and done all the porting and cylinder head work for many of the fastest Enfields on road or track. This is just to establish a basis for validation of my opinion on this.
The 650 twins power goals can easily be met with a 2 valve head arrangement. It could also have been met with a pushrod valve train instead of SOHC. It also didn't need a 6 speed gearbox because it has a broad torque curve. No need to dance on the shifter like a typical sportbike.
The fact is that these were all marketing decisions because Enfield had been derided for many years as being behind the tech curve regarding engine design, and they desperately wanted to shed that image in the minds of reviewers and customers. People who read magazines and are not engine designers are often influenced by other bike designs that are fast, and conclude that 4-valve OHC 6-speed slipper clutch systems must be needed because superbikes have those.
Now, I am not saying that there is anything inherently wrong with these design features. Certainly they are applicable in very fast high-revving superbikes. They can even be good for grocery-getters, but they are not necessary for such riding.
The advantages of 4-valve OHC designs is short and light valve train for high revving, which means higher than 7250 rpm. There is also a breathing advantage from larger valve area, which primarily evidences itself at the lower valve lifts, and needs a bit less valve lift for getting the necessary flow rates, compared to a 2-valve pushrod layout. These are good things, and I don't discount them, but when deciding on what is needed for an application and complexity/cost involved, it is very questionable for a 48hp (at the engine)650 twin with a 7250 red line.
For example, we have an advanced design 2-valve billet cylinder head for the 535 Continental GT which gives ~45 hp at the engine in full street tune at 6500 rpm. It could go higher, but the max limit of the Power Commander can only be extended to 6500 with Dynojet permission, so that's where we stop for normal street applications. It has only a slightly larger intake valve that stock(1.8"), but the entire internal head design is different and more modernized for flow and combustion efficiency, while appearing very similar externally, and staying compatible with the rest of the stock engine stuff, for the most part.
It is very expensive, but mostly because we have to make one at a time, and have zero economy of production scale. If we were making 500,000 a year like RE, it could be very low cost.
So, to sum up, there are reasons beyond performance for having certain features that could be matched by well-engineered systems that seem to be less exotic. Marketing buzzwords can make sales, even if they might not always result in more power.
