| Nissan has developed a new engine mechanism that enables both high power of turbo engine and low fuel consumption of non-turbo engine.
Features of VCR piston-crank system 1. The newly developed piston/crank mechanism (multi-link type) enables optimum compression ratio control. 2. For example, the fuel economy of a non-turbo engine and the power output of a turbocharged engine can be achieved in one engine. 3. By the ideal piston motion of multi - link, significant vibration reduction has been obtained. 
Technical explanation
New piston crank mechanism
By applying multi-link mechanism, significant improvement of engine vibration coupled with friction reduction (basic condition of engine mechanism) have been obtained. And in addition, function of variable compression ratio control under engine running condition has been achieved. 
Example of CR control (turbo engine)
The highest compression ratio is used in city driving to increase thermal efficiency for improved fuel economy. The system shifts to a low compression ratio for super charging when accelerating or climbing hills. This enables also higher turbocharging for much power while suppressing engine knock.
Low vibration nature of multilink mechanism
Piston motion in the conventional mechanism is essentially asymmetrical, with rapid motion occurring at top dead center. That unbalance deteriorates engine vibration in the case of conventional 4-cylinder engines. With the multilink VCR mechanism, the piston’s reciprocal action achieves ideal simple harmonic motion, resolving the unbalance. This enables low vibration property of in-line 4 cylinder engine close to that of V type 6 cylinder engines.
Found Here
Raj 
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More info on the VCR engine. - 
