Innovative Engine Tech? On a clear day you can see Infiniti!

Okay. So . . . what’s all the hype about Infiniti’s variable compression ratio, 4-cylnder, turbo engine? I’ve read the technical description and I’ve studied all the videos and the cutaway models. Basically it’s just another piston engine with a wonky mechanical linkage connected between the crankshaft and the connecting rods . . .

Eschew on that thought while I segue to a bit of history.

There was a time when the speed limit in Nevada was Reasonable and Proper. That meant you could drive any vehicle flat out, up to its maximum speed, as long as you were doing it under conditions that did not endanger yourself or other drivers. 

It also helped if Bill Harrah was a friend and eager to invite you to visit him in Reno and drive his latest Ferrari while you were there. We did that at Road & Track because Bill liked us and he enjoyed reading about his cars in our magazine. I also believe Bill trusted us because we treated all his cars with respect. They were driven hard, but never abused. And always retuned clean and full of gas.  

Bill Harrah loved cars and at one point his collection numbered more than 1400. I can remember walking through his warehouses where cars were lined up like cordwood. It was mindboggling in its enormity.

Harrah’s car collection was also the elephant burial ground for brilliant automotive technologies and engineering solutions that were, for one reason or another, before their time.  Little nuggets of technical curiosity. That weird engine over there? Oh, that’s an early attempt at a compound turbocharged engine. Never made it to production. Didn’t have materials that could take the heat at the time. 

What about that box of copper tubes and tanks looking forlorn over in the corner? Oh, that’s an early attempt at an advanced, compact steam engine. Worked great except they could never get the water to boil . . . 

And you know what they say: If you can’t take the heat, it’s only worth ditchin’.

Okay, let’s spool forward to the present and that Infiniti 4-banger. In many ways variable compression is the holy grail of IC engine technology. In theory it offers significant gains in efficiency, power, fuel economy and reduced emissions. And, yes, I was being more than just mildly facetious when I described it as a wonky mechanical linkage.

Reality? It’s more than a little like Bill Harrah’s collection of weird and wonderful auto tech. Nissan has known for a long time that its multilink mechanical system to vary the compression ratio would work. Problem is, the world of engine control technology has only recently reached the level of digital horsepower needed to precisely manage such a complex system. So it’s taken two decades for Infiniti VC-Turbo technology to reach production under the hood of the new 2019 QX50. The engine uses several advanced technologies, including port and direct fuel injection, variable valve timing, a four circuit cooling systems, plus a turbocharger. All of these systems provide inputs to the engine's computer. 

An electric motor controlled by the computer operates the multi-link system, increasing or decreasing the piston stroke and instantly selecting the most suitable compression ratio based on driver inputs and the car’s driving condition. The engine is able to offer any compression ratio between 8:1 (for high performance) and 14:1 (for high efficiency).

The twin balance shafts required by a typical inline four-cylinder engine to improve engine balance are no longer needed because of the more symmetrical piston motion compared to a conventional connecting rod and crankshaft. In addition, there is reduced side thrust on the pistons, which offsets some of the additional friction caused by the complex linkages. 

A low-friction mirror bore coating contributes to a 44-percent reduction in cylinder friction, allowing the engine to rotate more smoothly. The coating is applied to the cylinder walls by a plasma jet, then hardened and honed to create ultra-smooth cylinder walls.

The following chart compares the VC-Turbo 2-liter 4-cylinder to the previous 3.7-liter V6 it replaces. The new VC-Turbo produces less horsepower than the V6, but more torque at considerably lower rpm. And those 280 lb-ft of torque are available from 1600 up to 4800 rpm. 

Equipped with the VC-Turbo engine, the 2019 QX50 delivers 27 mpg (combined) for front-wheel drive and 26 mpg (combined) for all-wheel drive models. For FWD, this is a 35-percent improvement in fuel efficiency over the previous V6 engine, while the AWD model's 26 mpg represents a 30-percent improvement.

The QX50's 2.0-liter VC-Turbo engine also employs the world's first active engine mount vibration damping system, called an Active Torque Rod, to reduce engine noise even further. The 2019 QX50 is the only vehicle in its class to offer this kind of technology.

Numbers are numbers. How does the engine drive? It feels quite normal, which, I’m sure is what Infiniti was striving for. Matched to a CVT there is strong, smooth acceleration, and with max torque available at a diesel-like1600 rpm, the feel of torque is immediate. The only time you sense any turbo lag is a very slight hesitation when you tip into the throttle hard from idle. Can you sense the varying compression ratio? Not really . . . unless you check the indicator in the gauge cluster. Can you tell the engine doesn’t have balance shafts? Nope. 

Infiniti describes this new engine as follows:

INFINITI’s new VC-Turbo (Variable Compression Turbo) is the world’s first production-ready variable compression ratio engine. Promising to be one of the most advanced internal combustion engines ever created, VC-Turbo technology combines the power of a high-performance 2.0-liter turbo gasoline engine with the torque and efficiency of an advanced diesel powertrain – without the equivalent emissions.

Automakers press materials are sometimes full of hyperbole and hype. In this case I think Infiniti is right on with its description of this innovative engine technology. 

Enjoy the video that follows.