Engineering Explained Talks Infiniti's Variable Compression VC-Turbo Engine

While the work on Infiniti's VC-Turbo engine can be considered a 20-year, 300-patent story, the Engineering Explained piece of footage at the bottom of the page will break it down for you in under eight minutes - Jason, the YouTuber behind the channel, met the engine in the flesh earlier this month at the Detroit Auto Show.

We're talking about a turbo-four gas mill willing to offer the muscle of a six-cylinder powertrain, while delivering the kind of efficiency one would expect from the turbo-for diesel engine.

A variable compression ratio has been considered some sort of a holy grail of the engineering world for decades and here we are, talking about how this mill can go from 14:1 to 8:1.

Since we're dealing with a turbo mill, the latter value, which delivers the best knock protection, allows the unit to deliver its maximum output of 268 hp at 5,600 rpm and 288 lb-ft of twist between 1,600 and 4,800 rpm.

Nevertheless, when operating in 14:1 mode, the unit can deliver its maximum efficiency, as dictated by its combustion cycle (it can operate under the Otto and Atkinson cycles).

While the unit is offered on the QX50 SUV, a Car and Driver prototype drive from last November offers a few interesting details.

First of all, when the engine is matted to a CVT (continuously variable transmission), it can deliver a 3-4 mpg efficiency boost compared to the traditional 2.0-liter turbo-four engines powering German rivals such as the Audi Q5, BMW X3 or Mercedes-Benz GLC.

C&D was surprised by how... normal the engine felt, which is probably just what Infiniti engineers were aiming for: "The engine, mated to the CVT, felt very conventional. Acceleration was strong and smooth, the engine felt responsive, and it didn’t generate any funky sounds. Although the variable-compression mechanism takes about one and a half seconds to cycle between its ratio extremes, this interval is not apparent when you are cruising at a steady speed and call for more acceleration,"

In fact, it seems that the unit doesn't go too far from the driving experience offered by a modern turbo-four: "As in all turbocharged engines, response is not instantaneous, but between the time it takes for the turbo to spool and the CVT to shift ratios, the QX50 responds quite normally. Mat the throttle from rest and there’s a bit of hesitation, just as there is in all turbo engines when you don’t resort to brake-torquing to build boost in advance,"

The VC-Turbo engine was also present on the Detroit-debuting Q Inspiration Concept, which previewed Infiniti's future design language.

P.S.: We'll remind you that Porsche had previously trademarked a variable compression ratio, but we have yet to see the tech making it into the real world. Who knows? Perhaps the next-gen 911, which is currently in its advanced testing stages, will change this.