Billzilla wrote: ↑
Mon Sep 12, 2022 10:13 pm
With those valve and bore diameters, the valve timing must have little-to-no overlap. Looking at the cross-section of the heads in that first video pretty much confirms that I think. Small amounts of lift with one valve seems to largely preclude the other from lifting as well.
neither the exhaust valve period (that I quoted) nor the exhaust system design correspond to large overlap
ie they were normal for the supercharged era
the era started by Mercedes & Fiat c.100 years ago - (the 2 valve large VIA fashion came from NA Fiat design diaspora)
at first boost was at limited to high rpm only
https://motorsportmagazine.com/archive/ ... -1922-1925
(btw the very successful Sunbeam (NA 2 litre) GP car had a 3 speed gearbox (saving length/weight) ...
some earlier famous NA cars ie Peugeots had such large ports and valves they had 5 speed gearboxes)
high mechanical supercharging wouldn't develop worthwhile 'tuned length' exhaust effects
then with NA F1 (emulating GP motorcycles) overlap became important and designers chose smaller VIAs