SwampTiger
Airman
- 10
- Dec 15, 2020
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Inclined valves work when intake inclines towards exhaust. AIUI, in the Bristol engines, the intakes inclined/moved towards one another, not parallel. Same but less limiting for the exhausts.
For the A-S engines, I got the info off Wiki. My bad.
Still, why didn't Bristol, or a licensee, change the layout/pathway for the valves?
According to Lumsden, the early Leopards had 4 valve heads. They look to operate in a similar fashion to the Bristol actuating system.
Thanks Simon
Any pictures?
This is the Pegasus valve gear - looks a nightmare on paper but much better in the flesh.
This layout was designed in the 20's and it was very advanced for the time. Bristol engines were the first to solve the problem of valve burning thanks to their design: two smaller valves are easier to cool than one large, plus the exhaust valves are placed at the front thus they're better cooled by the incoming rush of air. The penta roof chamber was also a novelty (though it was used in some race cars at the time) and provided better combustion.So how did the later twin row Alfa 135 and Nakajima four valve geometry compare? Did they follow the Bristol pattern of intakes inclined to open towards one another rather than parallel to each other?
From a modern design perspective, this appears a poor design. Does anyone have access to discussion of reasoning? Compared to early two valve designs, it would be superior. However at the low compression and timing of earlier engines, it may not matter. The layout should enhance flow rate and turbulence. But why not improve the design over time?
Was the issue the conservatism at Bristol, and by other manufacturers, to limit costs, and thus changes to the design? They were able to keep up with competitors through the mid to late Thirties without major design changes. Bristol never made a two row poppet valve engine.