Is Infiniti's Variable Compression Turbo the Holy Grail of Power and Efficiency?

Henry Leung
by Henry Leung

It was 1998 and my friend Tom had just picked up a 1991 Eagle Talon TSI AWD.

“Ok, go ahead and floor it, but don’t rev it past 5,000 rpm,” Tom said.

I mashed the throttle and … nothing happened.

We were moving, but it was at the pace of a Toyota Corolla and nowhere near the rate of acceleration promised by the 2.0-liter turbo’s claimed 195 horsepower.

Disappointed, I left my foot on the throttle for a few seconds. Suddenly, I heard the whistle of the spooling turbo and a sudden shove of boost kicked in.

Four-cylinder turbo engines from the ‘90s were all similar to this. While they generated relatively big power at the top end, they also suffered from massive turbo lag and had fuel economy similar to a much larger V8.

Nissan’s new Variable Compression Turbo engine promises big power, minimal turbo lag, and decent fuel economy using some new trickery.

Is this the holy grail of turbocharged motors?


Why it matters

Infiniti’s introduction of its Variable Compression Turbo (VC-T) engine at the Paris Auto show was the big engine technology news from last month. Infiniti claims its new engine generates superior power and fuel economy compared to similar four-cylinder turbocharged motors.

The perfect turbo motor would have a low compression ratio to prevent knock and enable big power when the turbo was feeding it copious amounts of atmosphere, then switch to a high-compression ratio when off-boost to promote fuel economy and responsiveness.

We’ve been talking about variable compression engine designs for decades. The ideal pairing for a variable compression engine is with a turbocharged motor as it can take advantage of the low compression ratio to generate power without compromising fuel economy.

The closest OEM to production previously was Saab, which had a working prototype turbocharged 1.6-liter five-cylinder engine in 2000 known as Saab Variable Compression (SVC). The SVC engine was fairly complicated and had the entire head pivot on the crankcase to vary compression. Saab had a long history with turbocharged four-cylinder engines and this looked like the next development. Unfortunately for Saab, GM took over the company in 2000 and, as a result of shared engines with GM, the SVC engine was never put into production.

Nissan’s VC-T is a completely different design.

Originally filed as a patent in 2001, Nissan has worked on the technology for over a decade. The variable compression system works by varying the cylinder stroke. A complex, multi-link system changes the length of the stroke depending on the angle of a diamond-shaped center link, which is rotated by an actuator controlled by an electric motor. Using this system, the compression ratio can be changed between 8:1 to 14:1 in less than 1.5 seconds. The linkage does add some weight to the design; Nissan’s engineers have admitted that it’s probably 25-pounds heavier than a comparable fixed compression engine.

Henry Leung
Henry Leung

When he's not writing about cars, Henry is driving his GTI to construction sites and transporting his kids to preschool. Henry is a professional engineer, road biker, marathon runner, and lives in Vancouver, Canada.

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  • CrackedLCD CrackedLCD on Oct 28, 2016

    So… 25% better economy than their gas hog V6. Really swinging for the fences at Nissan, aren't they? Maybe I'm a fool but the numbers just didn't seem that impressive. A little more HP & torque, basically the same MPG, doesn't really scream "a decade's worth of innovation". You guys probably know by now I'm always gonna pine for a diesel, emissions be damned, but… in an SUV they really do make more sense. They have the torque to pull those square boxes along nicely and still get ~25-30 mpg average, which seems to be better than the units in the comparison box with this article.

  • Amca Amca on Oct 29, 2016

    I have yet to see anything about what the top end of the engine is. I'm betting that it's low. All that reciprocating mass. I'm also wondering whether with all that reciprocating mass also makes for a rough running unit. We haven't heard anything yet from a journalist who's driven one. I'm waiting.

  • Lorenzo Heh. The major powers, military or economic, set up these regulators for the smaller countries - the big guys do what they want, and always have. Are the Chinese that unaware?
  • Lorenzo The original 4-Runner, by its very name, promised something different in the future. What happened?
  • Lorenzo At my age, excitement is dangerous. one thing to note: the older models being displayed are more stylish than their current versions, and the old Subaru Forester looks more utilitarian than the current version. I thought the annual model change was dead.
  • Lorenzo Well, it was never an off-roader, much less a military vehicle, so let the people with too much money play make believe.
  • EBFlex The best gift would have been a huge bonfire of all the fak mustangs in inventory and shutting down the factory that makes them.Heck, nobody would even have to risk life and limb starting the fire, just park em close together and wait for the super environmentally friendly EV fire to commence.
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