2015 Volvo S60: Twin-Charging That Just Works
by Carlos Lago, Road Test Editor on November 20, 2015
Computer graphics in film work best when you don't see it. Mad Max: Fury Road used tons of CG, but it wasn't obvious. The effects improved scenes in ways you didn't notice while sitting in the theater watching a rad movie. The engine in our 2015 Volvo S60 is less rad, but similar. It is remarkably complex, but this complexity is invisible to its driver.
The 2.0-liter four-cylinder engine is twin-charged, meaning it uses both a turbocharger and a supercharger. This has always been an interesting concept, but much like how Rube Goldberg machines are interesting. A few rally cars famously employed the concept in the 80's, though it's been uncommon in production cars.
What's the concept? Let's back up a bit.
Both a turbocharger and supercharger are means of compressing air before pushing it into the engine, but they go about it in different ways. This gives them different strengths and weaknesses, broadly speaking.
The compressor in a supercharger is driven by a mechanical connection to engine, so it starts turning immediately when the engine does. The downside is that this mechanical connection consumes some engine horsepower. The compressor in a turbocharger is driven by the exhaust gas your engine already makes, so it doesn't cost you any horsepower.
This is great if you're always at full throttle and producing a steady stream of exhaust. But when you're in stop-and-go traffic, your engine seldom produces enough of a stream to power the turbocharger effectively. Most modern applications use one method, leaning towards turbochargers because the "free" exhaust stream doesn't hurt gas mileage as much as a mechanically connected supercharger.
So why use both? Well, the supercharger starts working as soon as the engine turns, so it works well at low engine speeds. The turbocharger, conversely, starts working better when the engine is spinning at higher speeds. The twin-charging theory means getting the benefits of both.
Yes, there's a lot of stuff happening under the hood, but the S60's trick is that you don't notice it. You can't sense when the supercharger's working or when the turbocharger kicks in. To the driver, it simply feels like the work of a responsive and powerful engine.
It also feels like a larger engine, which it isn't. I constantly forget it's a small four-cylinder because it feels like a six (it doesn't help that Volvo retains the T6 badging). The power rating is also what you'd expect of a six-cylinder: 302 horsepower and 295 pound-feet of torque.
It isn't the power alone, but the character. At low speeds during traffic or from a stop light, where the majority of real-world driving happens, a light and quick press on the gas pedal wakes up the supercharger, and the engine immediately supplies power. If the engine were merely turbocharged, there'd be a small delay between pressing the gas and the rush of power.
While our fuel economy has consistently fallen under the EPA's rating, I still enjoy driving the S60 because the engine makes it feel so brawny. Nobody expects to get outmuscled up the on-ramp by a Volvo.
Too long; didn't read? Our Volvo S60 is like "Mad Max" because combining turbochargers and superchargers is cool.
Carlos Lago, Road Test Editor