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It would be nice if someone could come up with sectional drawings of the VK-107 because this was the version that featured four valves per cylinder.
Given that the inlet and exhaust ports were on the same (outer) side of the cylinder blocks, then the cylinder head must have been cross-ported, similar to the Packard A1500/2500 engines of the 1920s.
Lage (p 259) says the two intake valves had differential opening. One allowed the entrance of air/fuel mixture from the carburettors while the other fed in only pure (compressed) air from the supercharger feed pipe. The air-only valve opened 65 deg. before the other and closed 82 deg later.
To operate the valves, three cams (presumably from the single OHC) per cylinder were employed. One probably operated the two exhaust valves via a tee-type cam follower but just how the two inlet valves were controlled would need an explanatory drawing.
I would be interested in an English language version of Birkigt's reasoning around the use / advantages of this 'differential scavenging' concept.
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Gunston (p173) says, "the exhaust was taken out from both sides of each cylinder, so that, in addition to the usual six ejector stubs on each side of the nose cowling there were two more rows of six along the top."
I have had a look at a few photos of the YAK 9 aircraft and I can not see any pipes sticking up from the top of the cowling. If there were, they would surely impede the pilot's view but certainly defrost his windscreen!
The problems of co-ordinatiating two valves (9 10) plus two independently timed inlet valves to give proper running of the engine at all heights and all power settings would have been considerable.
Do not forget that VK-107 project began in early 1940 and few of the first engines were installed on LAGG-3 in autumn 1941. So the most sense of such cyl. heads' complicity was to keep as much technology of previous VK-105 as possible.Even so, the cylinder head on the Russian engine was COMPLICATED! Hope it was all worth it in terms of a better running and more powerful engine.
As for me, I do not know what is in the yellow circleBretoal said:Question (or quizzz...) : What is in the yellow circle ???
Alain