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Infiniti's new VC-T changes the rules of small turbocharged engines

The upcoming Infiniti QX50 crossover does not get our pulse racing, no matter how shapely the QX Sport Inspiration concept that previews it may be. No midsize SUV does, to be fair. But it has something special under the hood – the world's first production variable-compression-ratio engine. That means the QX50's 2.0-liter turbo four, which makes 268 horsepower and 288 pound-feet of torque, will have up to 27 percent better fuel economy. Here's how it works. The trend of moving to smaller, turbocharged engines carries with it one big falsehood. Under low load when the turbo isn't needed, these engines are less efficient than an equivalent engine without a turbo because of the low compression ratio the turbo requires. That is, if you never need the extra power, you're wasting fuel. Turbocharged (and supercharged) engines use a lower compression ratio to prevent detonation. When you force extra air in a cylinder and mix it with fuel, it's more likely to prematurely go boom. Lowering the compression ratio prevents this problem, but it's less efficient. Infiniti's VC-T promises the best of both worlds, with a compression ratio that ranges from 8.0:1 for high-power turbo needs to a 14.0:1 ratio for fuel-sipping efficiency. At its heart the VC-T engine is a simple idea, but it's complicated to explain. Consider yourself warned. The photo below from Infiniti serves as a good visual overview. For the truly nerdy, this patent application covers the mechanical concept. Instead of having the pistons connected to the crankshaft, Infiniti's engine has a pivot arm with a connection on each end. One end connects to the piston, the other connects to a second lower shaft, which is controlled by an actuator arm. At any given time the engine's pistons move up and down according to the lobes on the crankshaft. But the actuator arm can change the angle of the pivot arm up and down. That is, the pistons still move in the same motion with the same stroke, but phase the entire stroke up or down. Move the pivot up and there's less room at the top, which means a higher compression ratio. Move the pivot down and the compression ratio goes down, too. As an added bonus, the lower shaft eliminates the need for counter-rotating balance shafts. Infiniti says this system works constantly and can vary the compression ratio to any number between 8:1 and 14:1. It also uses electronic variable valve timing on the intake valves to switch into Atkinson-cycle combustion for greater efficiency.

Infiniti's variable compression engine in the 2019 QX50 is the first of its kind

The world's first variable compression ratio engine is here, in a production car. That car is the 2019 Infiniti QX50, debuting this week at the Los Angeles Auto Show. The midsize crossover has seen a refresh that has brought it an all-new platform together with new driver assist features, but it's the engine that's the centerpiece here. Nearly everything is continuously variable under the hood of the QX50 – not only the new shift-by-wire XTRONIC CVT. The new VC-Turbo gasoline engine is able to change its compression ratio from 8:1 to 14:1, or anything in between depending of the driving situation; whether there is need for top-end power or turbodiesel-like torque from low revs, or optimized fuel economy. The pistons' reach is continuously adjusted by an electric "Harmonic Drive" motor, which controls a multi-link system, affecting the top-dead-center of the pistons and changing the compression. The engine can also switch between efficiency-maximizing Atkinson cycle and regular combustion cycle, on the go – and there's both multipoint injection and gasoline direct injection employed. The result is 268 horsepower at 5,600 rpm and 280 pound-feet of torque at 4,400 rpm; good figures for a 2.0-liter four-cylinder gasoline engine with a single-scroll turbocharger. Infiniti says that the FWD version's fuel economy of 27 miles per gallon combined is 35-percent better than the previous-generation V6 engine; in AWD guise, it reaches 26 mpg, which is a 30-percent improvement. The new engine is pretty much all-aluminum, but the vaguely magical-sounding "transformative multi-link components" behind the variable compression system are made from high-carbon steel alloy. The engine's multi-link system also enables it to do away with any balancing shafts, and Infiniti compares its smoothness to a V6 rather than a regular four-cylinder. In addition to the aforementioned tech, the VC-Turbo engine has the world's first active engine mount vibration damping system to smoothen its operation even further. Related Video:

Driving the Honda Ridgeline and marveling at Tesla | Autoblog Podcast #638

In this week's Autoblog Podcast, Editor-in-Chief Greg Migliore is joined by Consumer Editor Jeremy Korzeniewski and Associate Editor Byron Hurd. They start off talking about why more people should buy the Honda Ridgeline, because it's a pretty darned good truck. Next, Byron talks about some Hyundais. He shares his experiences with the 2020 Sonata Hybrid and talks briefly about the prototype 2021 Elantra currently occupying his driveway. Up next, Jeremy shares his feelings about the BMW X1 crossover he spent some time with, prompting the gang to mull over the notion of BMW's modern interpretation of "Ultimate Driving Machine." After that, Byron talks about towing his 1990 Mazda Miata with the 2020 Infiniti QX80, and then they wrap up with some discussion of the mystery surrounding the Ford Maverick and some comments on the current state of Tesla. Autoblog Podcast #638 Get The Podcast iTunes – Subscribe to the Autoblog Podcast in iTunes RSS – Add the Autoblog Podcast feed to your RSS aggregator MP3 – Download the MP3 directly Rundown Hauling dirt with the 2020 Honda Ridgeline Driving the 2020 Hyundai Sonata Hybrid Discussing the 2021 Hyundai Elantra Driving the 2020 BMW X1 Towing a 1990 Mazda Miata with a 2020 Infiniti QX80 News Ford Maverick tailgate stamping leaks; we may see the whole thing in 2021 Tesla reports profit for fourth straight quarter, setting it up to join S&P 500 Feedback Email – Podcast@Autoblog.com Review the show on iTunes Related Video: