Infiniti's VC-Turbo Engine Is The First Variable Compression Engine

Infiniti's VC-Turbo Engine Is The First Variable Compression Engine

Over the last 20 years Infiniti has been attempting to crack the code on the variable compression engine, and as of this year it seems as though they have succeeded. After more than a hundred engine prototypes ad almost 2 million miles of road test, the VC-Turbo engine is ready to hit the road in their 2019 Q50 SUV.

The compression ration of most engines is fixed, with a ratio like 10:1. It's a way of measuring the maximum to minimum volume of a cylinder as the piston makes a complete stroke. The first number is the volume when the piston is at the bottom of the stroke while the second is when it's at the highest. If an engine has a high compression ratio, it means that the volume of air and fuel in the cylinder is being squeezed into a smaller space than an engine with a lower compression ratio.

The difficulty in deciding on a specific compression ratio is that one size does not fit all. Different ratios are better than others under different circumstances. Having only one fixed ratio leads to issues with engine wear, fuel economy and horsepower. What would happen, however, if en engine could change its compression ration to optimize under different circumstances?

Enter the VC-Turbo. After extensive testing and a ton of money spent on R&D, Infiniti has produced an engine capable of changing its compression ratio from as low as 8:1 to a max of 14:1. Thanks to its ability to change the actuator arm's reach, the engine's computerized systems can determine when to use the turbocharger more or less under different circumstances. The balancing act between piston reach and turbo charging gives the best of both worlds: performance and economy. The overall result of this blending gives a counterintuitive result, though. While the measurable horsepower versus previous year's models is markedly lower, the torque generated is higher. This is reflected also in a significant reduction in engine wear with no detectable knock and a lower noise profile than previous models.

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Written By: Todd Hendrickson
Source: Popular Mechanics