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

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.