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Infiniti’s 2019 QX50 is the first vehicle in their lineup to feature their VC-Turbo (Variable-Compression) engine that can change compression ratios on the fly for increased fuel efficiency. Standard automobiles typically have a single compression ratio that is expressed in a form such as 10:1, which compares the maximum to the minimum value of cylinder volume as the piston travels throughout its cycle. Simply put, higher loads require lower ratios to maintain efficiency, and vice versa.
The engine works using a computer that signals an electric motor that moves an actuator arm to shorten the reach of the pistons inside the engine, which lowers the compression ratio during times when higher turbo boost is being used, giving the vehicle increased power efficiency. When the motor isn’t utilizing the turbocharger as often, the actuator arm lengthens the pistons travel, which ups the compression ratio.
The VC-T engine can also function in the Atkinson cycle to further boost efficiency, which works by slightly opening the motors intake valves, drawing in extra air into the combustion chambers at the same time the pistons begin to compress the air-fuel mixture. This allows the engine to act similar to a smaller, more efficient motor when turbo power isn’t needed.
When the vehicle ignition is underway, the VC-T generates power like a bigger engine, and when it comes under high-pressure, it switches over to the Atkinson cycle as the motor has enough power to spare, thereby retaining its efficiency. Infiniti’s VC-T engine is currently only available in the company’s 2019 QX50, but we can surely expect to see it in Infiniti’s future lineup.