A look inside the Infiniti VC-Turbo engine

PHOENIX -- When you think about it, just about all the improvements made to the internal combustion engine in the last hundred years have been bolt-on items that left the rotating mass -- the pistons, crankshaft and rods -- unchanged.

Yes, the camshaft moved in some engines from below the cylinder head to above it. But regardless of the location, the cam still looks the same and does the same thing: open the valves.

The carburetor has given way to fuel injection; electronic ignitions have replaced the points and condenser. In other words, nearly all the components and systems that make the internal combustion engine run have seen massive improvements that also have improved the engine's efficiency.

But take a crankshaft and rods from an engine made a century ago and compare them to today's parts, and you won't see much change.

And that's why the variable compression engine debuting next year in the 2019 Infiniti QX50 is a really a big deal -- a major reworking of the basic operating principles of the piston-driven internal combustion engine. That hasn't happened in our lifetime. And, now that we are at the dawn of the electrification age, it may not happen again.

Infiniti calls its 2.0-liter four-cylinder engine the VC-Turbo, and its engineering layout is ingenious. An elliptic device attached to the crankshaft where the rods go changes the distance the pistons travel in the cylinder by as much as 6 mm, or about a quarter of an inch. That varies the compression from 8.1 to 14.1. The result is V-6-like performance with four-cylinder diesel-like fuel economy -- with none of the image baggage or cost of the diesel.

Two weeks ago at Infiniti's proving grounds here, I got a chance to look inside a cutaway of the engine. Nothing works like you think it does. Looking at the moving parts -- and there are a lot more of them in the VC-Turbo -- I was thinking the engine must lose a lot of power because of parasitic losses or internal friction.

In a regular engine, the major friction points are on the crankshaft assembly, both ends of the rods and the piston traveling up and down in the cylinder. In the VC-Turbo, each piston is connected to a multilink device with a rod on each side, one of which mates to a control shaft. That's the part the electronic actuator pushes to change the piston travel and thus the compression. In other words, there are a lot more moving parts. And about 22 pounds more weight than a regular four-cylinder turbo.

But Shinichi Kiga, Nissan's chief powertrain engineer, told me the VC-Turbo engine creates less friction than a regular engine. The secret: Nissan engineers moved the crankshaft out from being directly underneath the pistons' bores and offset it about 15 degrees. That, in combination with the multilink assembly, eliminates the usual side forces that act on a piston as it travels in the cylinder. In other words, the piston is pushed and pulled straight and up down in each cylinder.

Behind the wheel of a test 2019 QX50 with the VC-Turbo engine, I experienced strong low-speed torque, no perceptible turbo lag and impressive acceleration all the way up to around 100 mph. But what I really liked -- and I made sure Kiga knew it -- was the sound of the engine. At wide open throttle, the VC-Turbo engine sounds glorious as it revs.

Kiga says the multilink variable compression technology could also be used in a three-cylinder engine to replace a four-cylinder, but it is not a great fit for V-6 and V-8 engines.

Here's my prediction: This VC-Turbo engine could go down as one of the most loved ever made by Nissan. It excites the senses with great sounds. It delights with impressive performance. And it should sip fuel.

In the QX50 compact crossover, the VC-Turbo is replacing a big V-6. In a lightweight car, the performance and fuel economy would probably set the standard. And it would be a marvel.

You can reach Richard Truett at rtruett@crain.com

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