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2020 Hyundai Sonata 1.6T vs. 2020 Nissan Altima 2.0 VCT: A Tale of Two Techie Turbos

Motor Trend logo Motor Trend 4 days ago Motor Trend Staff

a car parked in a parking lot: 2020-Nissan-Altima-12.jpg
Engine design is even harder than 21st century democracy because it requires even more compromise. Every design parameter "knob" that engineers can turn affects an engine's power, fuel efficiency, and emissions, and clever solutions to hack long-established trade-offs between them generally compromise cost, durability, and refinement. Nissan's recent hack is to vary the compression ratio, and now Hyundai is introducing the world's first variable valve-duration camshaft. These two very different approaches seek a similar effect: enable strong turbo boost for performance without inducing knock (which demands a lower compression ratio), while enhancing low-load fuel efficiency by expanding the combustion gases as much as possible (expansion ratio is the piston-going-down mirror image of compression ratio).

a car parked in a parking lot: 2020 Hyundai Sonata vs 2020 Nissan Altima© Motor Trend Staff 2020 Hyundai Sonata vs 2020 Nissan Altima

Nissan's 2.0-liter VC-Turbo four-cylinder engine uses an elaborate linkage system to alter the piston stroke (and displacement, slightly), thereby providing a turbo-friendly 8.0:1 compression ratio when needed, and a fuel-sipping 14.0:1 expansion ratio while loafing along. Hyundai's CVVD concept is perhaps even more elaborate (at least from a parts-count perspective—see our companion feature to this tech comparison) and manages to vary the length of time the intake valves stay open, so the effective compression ratio (compression that happens after the intake valve closes) can be way less than the expansion ratio.

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Hyundai doesn't use the low effective compression ratio for power, though. Here the power mode is to open and shut the valves quickly with negligible exhaust-valve overlap, trapping and compressing as much intake charge as possible and taking full advantage of the fixed mechanical compression/expansion ratio of 10.5:1 (the cooling effect of direct injection helps reduce knock). It's under light loads that the intake valves stay open until the piston is well on its way back up. The crankshaft does less work pushing the piston up with the intake valve open, but the combustion gases keep pushing on the piston all the way down so efficiency improves.

There is, of course, a lot more to this new 1,598cc Smartstream engine than its fancy cam drive. The bore shrinks and the stroke extends relative to the outgoing 1,591cc turbo (from 77.0 x 85.4mm to 75.6 x 89.0mm)—providing those combustion gases a notable 3.6mm of additional room to expand. The fuel injection pressure increases from 250 to 350 bar (roughly 3,600 to 5,100 psi), to be sure enough fuel can be injected and atomized after the late intake-valve closing. Redesigned intake runners generate more charge-air tumble to ensure thorough mixing. And because adding stroke inherently adds friction, as does the new CVVD system, extensive friction-reduction measures were taken throughout the engine: smaller journal bearing diameters and polymer coated bearings, lightened pistons, a lower-friction cam chain drive, and new roller-swing-arm valve actuators. Overall engine friction is said to be down 34 percent. Integrating the exhaust manifold into the cylinder head reduces heat lost to the exhaust, while the smaller bore and a new integrated heat management system help reduce heat lost to the cooling system for improved thermal efficiency.

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The 1.6-liter TGDI Smartstream engine is rated to produce 180 hp at 6,000 rpm and 195 lb-ft at 1,500 rpm, up from 178 hp at 5,500 rpm and identical torque on the outgoing 1.6T. That's just a 1.1 percent boost in peak horsepower, but Hyundai claims that over the engine's entire operating range, performance is improved by 4 percent while brake-specific fuel consumption over the entire operating range of the engine improves by 5 percent relative to its predecessor. Sadly, the EPA didn't find that 5 percent bump on its test cycle—the 2020 Sonata 1.6T earns a 28/37/31 mpg EPA city/highway/combined rating; the outgoing model was rated 27/36/31.

We've heard the cost came in at about $200 per engine. If so, it likely represents a huge discount over what we infer Nissan/Infiniti spends on VC-Turbo. At the time the system was released, Nissan engineers claimed they spent about half the going rate for reducing a single gram/km of CO2 emissions (which they pegged at $70 to $80). In switching from a V-6 to the VC-T engine, both the Infiniti Q50 and the Nissan Altima saved 22.5 g/km on the EPA cycle, so that puts their system at $800.

So how do the two engines drive? The VC-T engine only comes mated to continuously variable transmissions, and that's an unhappy marriage. There's always too much variability happening at any one time, resulting in nonlinear, unpredictable acceleration under most driving conditions short of foot-to-floor drag-racing. At wide-open throttle, it goes like stink, delivering on its V-6-performance promise. The rest of the time, in the vehicles we've sampled, we've struggled to find the four-cylinder fuel economy. We long-term-tested an Infiniti QX50 SUV with a VC-T engine, and in our Equa Real MPG real-world fuel-economy testing it underperformed the EPA's 24/30/26-mpg city/highway/combined results by 14 percent in the city and 7 percent combined. Worse, though, was our 23,000-mile average of 20.8 mpg—fully 25 percent below the EPA combined rating, and about what we'd expect from a V-6.

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In our drives in two high-end Sonatas equipped with the Smartstream 1.6T engine and a conventional eight-speed automatic, the valve-duration variability seems utterly unnoticeable, and drivability is quite pleasant. This is a much smaller engine in a similarly Altima-sized car, so it's towing about 4.5 more pounds per horsepower than the Nissan Altima engine is, so it's no surprise that the Sonata trails the Altima to 60 mph by about 2 seconds (8.2 versus 6.1 seconds). We have yet to fact-check the Sonata's EPA ratings with testing of our own, but the EPA reckons it'll best the Altima VC-T's 25/34/29 mpg rating by 2 mpg in each category. (Note that among small turbo family sedans, the Sonata ranks admirably close to the Honda Accord 1.5-liter turbo's 29/35/31 rating, though that car's 10-speed automatic and lower curb weight give it a 0.6-second advantage in 0-60 mph.)

We look forward to our first chance to fully test the performance and fuel economy of Hyundai's new CVVD system—and to test its drivability and durability in a long-term car.

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