Right you are, hence Yamaha`s on-going abandonment of the five-valve design. I recall reading that Ferrari experimented with the 5-valve design on its F1 engines some years ago and eventually ditched it too.
I had spoken to Kevin Cameron about this a few years back and he said that apparently the center intake valve stream causes turbulence, hence its inferior performance. Not sure if this was his opinion or if he had gotten the info first-hand from engineers (too loang ago now....)
Doesn`t Audi still use it on some of its high-performance engines?
99 VTR1000F Firestorm, a.k.a. The Carbon Express