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.
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- MrIcky It's always nice to see a car guy put in charge of cars instead of an accountant. I wish him well and look forward to some entertaining reveals. I think he and Gilles may be the only industry people that I actually enjoy listening to.
- Master Baiter It doesn't matter whether autonomous vehicles are better or worse drivers than humans. Companies with deep pockets will find themselves sued over incidents like this. Enough lawsuits and the whole business plan collapses. Cheaper to just put a human behind the wheel.
- MaintenanceCosts How many dogs are wiped out by human drivers annually?Which type of driver wipes out more dogs per mile? Per trip?Without some context there's not much information here.
- SCE to AUX I hope the higher altitude doesn't harm his zeal or his career.
- SCE to AUX Probably a fair price. This is a car I can't own, since it's not made for 6'6" people.
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.
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.