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Yea variable compression is not the lowest hanging fruit, not even close. The practical limit for mechanical compression ratios is maybe 14:1, for full throttle. At say 20-30% load there is a benefit to increasing the compression ratio even if the valve timing mechanism allows minimal pumping loss, but why not just introduce a little (cooled) EGR to bump up combustion pressure/temperature?
Forced induction with a high mechanical "compression ratio" (we're really looking for the expansion ratio here), and say "Atkinson cycle" intake cams to increase low load efficiency and decrease detonation tendencies is essentially variable compression ratio.
I feel like the "upgrades" that engines are actually going to see on a large scale are direct injection (already happening), further upgradess to cam phasing systems (can get rid of most pumping losses if the range of movement for the cams is larger), forced induction (as a cheaper way to get most of the benefits of variable compression, variable displacement, and more complex variable valve timing), cooled EGR (already happening), and maybe laser ignition or something of that flavor. These things are highly reliable, simple, and relatively cheap to design in, compared to things like fancier valvetrains, variable compression, HCCI, etc. which have many more technical challenges.
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