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Variable compression ratios: Infiniti's new main squeeze

It's only teasing a bit of information for now, but it will be properly unveiled during this year's Paris Motor Show.

More than 20 years in development, INFINITIís new four-cylinder turbocharged gasoline VC-T engine represents a major breakthrough in internal-combustion powertrain technology. VC-T technology signifies a new chapter in the story of the internal combustion engine ñ engines are no longer limited by a fixed compression ratio. The ingenuity of VC-T engine technology lies in its ability to transform itself and seamlessly raise or lower the height the pistons reach. As a consequence, the displacement of the engine changes and the compression ratio can vary anywhere between 8:1 (for high performance) and 14:1 (for high efficiency). The sophisticated engine control logic automatically applies the optimum ratio, depending on what the driving situation demands.
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You're not going to notice much difference here. It's still a traditional four-stroke, internal combustion engine, after all.


Just when you think we're approaching a point where we can't improve on a given technology, some automaker shows up with something new and wild. Infiniti's taught the internal combustion engine a new trick to raise its versatility a bit -- variable compression ratios.

Its VC-T (Variable Compression-Turbocharged) engine will debut officially at the Paris Motor Show later next month, but Infiniti's giving us a tease of its tech ahead of time. The engine is capable of changing its compression ratio on the fly. Compression ratio is the, er, ratio of maximum to minimum cylinder volume, and changing it can have dramatic effects on performance and efficiency.

Infiniti did not explain how it achieves this variable compression ratio, but the automaker claims a number of benefits from this technology, including lower fuel consumption and emissions, improved vibration and a more compact footprint than other engines. Infiniti told Reuters that the 2.0-liter VC-T engine improves efficiency by 27 percent over Nissan's 3.5-liter V-6, which it will eventually replace, with similar output figures.

While this may seem new and fancy, it's not the first attempt at creating a variable-compression engine. There have been patents filed for variable-compression rotary engines, and Saab designed a variable-compression engine, as well, but neither reached the market. GM shelved the latter after buying Saab, deeming its tech cost-prohibitive.

Varying compression ratios are also part of the Atkinson-cycle engine. Typically seen on hybrids and other efficiency-minded vehicles, Atkinson-cycle engines hold the intake valve open during the engine's compression cycle, effectively reducing compression ratio as the air escapes. We'll have to wait until the end of September to see how Infiniti's technology differs from the Atkinson cycle.