Subtle differences in the angle of the pent roof, the shape of the transition from pent roof to the squish parts, valve angle, and also not just in the chamber but the way that the YB has a nasty angle in the exhaust port which hinders flow and results in more heat.

Massively complex subject, and not one Im really qualified to comment on beyond on the basics, I certainly wouldnt be capable of designing a head like the honda engineers etc do, takes years of experience and trial and error mixed with some massively sophisticated computer hardware and software.

You have to remember the YB was designed by a couple of blokes who didnt have anything like the data available today, and had to fit on an existing engine which constrained where oil and water ways and head bolts were etc which has an impact on design too.

Also the YB head was developed for about 20 quid as an internal project at cosworth, would have been a different story with proper ford money behind it right from day one.



skyline is 6 cylinders, that changes everything, as its got more valve area as a result of having the extra valves, so the same cam results in less opportunity for airflow on the YB