They you could electronically adjust duration and maybe even lift, Also you could have less duration at low rpm's and more at high rpms.
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F1 engines have had pneumatic valves for a long while now. Renault have had hydraulic valve lifters on production car engines for some time. Renault have been experimenting with an electro-hydraulic valve for camless operation but it is still in development. The electro-hydraulic approach overcomes some of the inherent problems of an electro-mechanical arrangement.http://scarbsf1.com/valves.html
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They do exist. From the link below, volume production has just or will soon start.
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they do, but mechanical ones are more reliable.