Read Kevin Cameron's book "Classic Motorcycle Racing Engines" and you can see why all present day high performance engines are a pent roof design.
Rex
x2 Read & reread the chapter on Cosworth DFV's . . . . .
in percentage terms, how much more efficient is the Pent roof engine than Hemi's, ??,,
Da**!!!! Where do I start???
A) More valve area per cyl bore area
2) Less valve to valve clearance problems at high durations
d) Less valve C/L to bore angle & less port to valve C/L angle
m) Less chamber surface area for a given "volume"
z) etc, etc, etc . . . .
For mech F/I, 2V semi-hemis like Lotus T/C etc, running 9500 MAX rpm: 130/135 bhp/litre
For mech F/I, 4V cossie types like BDG's, BH420R's etc, running 9500 MAX rpm: 145/155 bhp/litre
Original Cosworth DFV spec was 405 bhp at 9000 rpm MAX, for 135 bhp/litre
Final Cosworth DFY spec was 520 bhp at 11,000 rpm max, for 173 bhp/litre
Most pessimistic differential +7.4%
Most optimistic differential +33%
Or do the math anyway you want.
Figure a conservative pickup of 5% even if your combo is not well sorted, due primarily to better low lift flow because of the larger valve area . . . . . .
Fordboy