How To Replace Your V6 in One Easy Step
Published: 07/12/2010
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by
Jason Kavanagh, Engineering Editor
Hyundai's rapid ascent to the front lines of automobiledom with cars like the 2010 Hyundai Sonata is underscored by this factual tidbit — the company's first fully homegrown engine, the so-called Alpha engine, debuted less than two decades ago.
While the Alpha was designed with a close eye toward the Honda D-series engine, today's 2011 Hyundai Sonata 2.0T suggests that the tables appear to be turning. It is now much more likely that the powertrain philosophy espoused by Hyundai will be emulated by others, rather than vice versa.
A Four-Pot Strategy
The 2011 Hyundai Sonata has proven that the Korean company is capable of building a no-excuses mainstream sedan. Later this year you'll be able to select a class-leading engine for it, too. Not that there's anything wrong with the base model Sonata's 198-horsepower 2.4-liter inline-4, but the natural approach among purveyors of family sedans is to also offer something with a little more punch.
Hyundai made it clear from the outset that the 2011 Sonata would not ultimately receive an optional V6. More power, it was promised, would come in the form of boosting. By applying direct injection and turbocharging to a downsized version of the Sonata's Theta II four-cylinder, the Hyundai engineers figure they've got their company's own 3.3-liter V6 power plant beat on all counts.
The turbocharged 2.0-liter — 2.0T, in Hyundai-speak — will be available in SE and Limited models of the 2011 Hyundai Sonata and will be offered only with a six-speed automatic transmission. Sonatas equipped with the 2.0T powertrain are otherwise unchanged from the normally aspirated variants.
A Twist on Turbocharging
Although direct-injected and turbocharged fours are becoming commonplace, Hyundai's 2.0T introduces an unusual wrinkle: The engine is required to sip nothing more exotic than 87 octane fuel. That is, the 2.0T generates its 274 horsepower at 6,000 rpm and 269 pound-feet of torque from 1,750-4,500 rpm on the cheap stuff. Typically, elevated specific output and low octane are mutually exclusive, making this achievement worth talking about.
Timothy White, the Sonata's senior powertrain engineer, reckons that this requirement amplified the difficulty of balancing low-end throttle response with a lofty peak horsepower target. This is because boosted engines generate high cylinder pressures, increasing their propensity for pre-ignition (knocking), which in turn limits how much grunt you can safely produce at both ends of the torque curve.
One bit of turbo trickery deployed in the 2011 Hyundai Sonata 2.0T is a fully electronic wastegate actuator (conventional pneumatic actuators are so last week). It allows a greater degree of control over boost than traditional actuators, but Hyundai has also found other benefits. For instance, the electronics can open the turbocharger's wastegate during cold starts to enable rapid light-off of the catalytic converter. In turn, this functionality allows the catalyst itself to be positioned under the floor, far away from the turbo, where it induces less exhaust backpressure than would a close-coupled catalyst. And backpressure is the enemy of power and response, especially when you're trying to make a lot of power on low-octane fuel. The e-gate (we just made up the term) also permits some trick tuning during part-throttle conditions. By opening the drive-by-wire throttle and manipulating boost, part-load pumping losses are reduced, improving fuel economy.
According to Senior Engineer Donghee Han, the development team experimented with about 30 different turbocharger configurations before settling on a twin-scroll Mitsubishi TD04-19T turbo. Hyundai engineers then pored over it in search of better boost response and improved durability. To wit, rotating inertia was improved by reducing the number of blades on the turbine wheel from 12 to 11.
The turbine housing — integrated with the exhaust manifold — is made of austenitic stainless steel and can withstand exhaust gas temperatures of 1,740 degrees Fahrenheit. This kind of tolerance for heat means the 2.0T doesn't need to rely as heavily on fuel enrichment to keep its exhaust bits cool, which further enhances fuel-efficiency.
Remember the Hyundai Scoupe Turbo? The 2.0T is nothing like that.
Bring in the Reinforcements
Hyundai didn't simply bolt this turbo to an existing Theta II engine, as numerous changes were made to enable the inline-4 to withstand the more severe conditions of turbocharging. The changes include a reinforced aluminum block (still with an open deck, however), beefier connecting rods of a different alloy than those in the 2.4-liter mill, pistons with thicker ring lands, oil squirters, plus new valves and valve seats that are tolerant of higher temperatures.
The new pistons also lower the compression ratio to 9.5:1. Boost pressure reaches 17.2 psi at 1,750 rpm and tapers to about 14 psi by 5,500 rpm, at which point the boost is reduced to prevent exhaust backpressure and also keep the turbo rpm from running away.
A lot of attention was paid to cylinder head cooling in order to stave off detonation. As Hyundai's White says, solving the puzzle involved "the combination of a lot of little things that all added up." Coolant passages in the head were enlarged thanks to smaller-diameter spark plugs. The front-mounted air-to-air intercooler received its own dedicated duct. Direct injection is key in providing a charge cooling effect, while the retention of hot exhaust gases in the combustion chambers is minimized through careful attention to manifold tuning.
Development tests for the new mill included 300 hours at wide-open throttle, followed by 20 hours of operation at 6,700 rpm (the rev limiter is set at 6,600 rpm in the car). While the durability testing included 87 octane fuel, engineers hint that the calibration of the 2.0T will automatically take advantage of higher octane — on premium fuel, peak horsepower goes up by about 10. And although peak torque is unaffected by the addition of premium fuel, the area of torque curve before the peak is said to plump up somewhat.
All That Tech Talk Is Great, but What's It Like To Drive?
We spent some time at Hyundai's Namyang Proving Ground outside of Seoul, South Korea, where we gleaned some driving impressions from behind the wheel of the 2011 Hyundai Sonata 2.0T.
Boost builds progressively from very low revs, and the 2.0T engine delivers power in earnest before the tach needle sweeps past 2,000 rpm. The transition from idle to boost is deceptively linear, as there's none of the wait-wait-wham! boost characteristic of many highly boosted four-cylinder engines.
Transitioning from part-throttle to full whack is similarly seamless — power simply builds in direct response to the position of your right foot on the pedal. The power delivery doesn't fall off during a gearchange, either. The 2.0T essentially drives like a larger-displacement, normally aspirated engine, a characteristic which will dovetail nicely with the sensibilities of those shopping in this segment. If you're looking for a rubber-bandlike driving experience, go buy a Subaru.
As with the base 2.4-liter, the 2.0T's engine noise is noticeable until you settle into a cruise. The engine note at big throttle openings is fairly prosaic, too, although the faint turbo whistle you hear provides a bit of character. From a standstill, Hyundai reckons the Sonata 2.0T will hit 60 mph in 6.5 seconds, which sounds believable.
No changes to the chassis or suspension are made when you tick the box for the 2.0T, yet the chassis feels entirely capable of coping with the turbo engine's additional twist. Traction in the admittedly ideal conditions we experienced never proved to be an issue, while torque steer is minimal. We'll have to see whether this holds true when trying to apply power on bumpy real-world roads, as the proving ground is pretty smooth.
All This and Fuel Economy, Too
Hyundai's obsession with details while creating the 2.0T engine would have been for naught if fuel economy suffered unduly. There's good news there, too. In fact, fuel economy might prove to be the 2.0T's most noteworthy asset, because Sonatas equipped with this new turbo mill manage 22 city/34 highway mpg, which is a penalty of just 1 mpg on the freeway compared to the base 2.4-liter.
Hyundai hasn't announced final pricing for the 2011 Hyundai Sonata 2.0T, only that 2.0T-equipped models will start "under $25,000." This bogey places the Sonata 2.0T in the same territory as V6-powered rivals like the Nissan Altima and Toyota Camry while undercutting the V6-equipped Chevrolet Malibu, Ford Fusion and Honda Accord.
With more power and torque and better fuel economy than any of those cars, the Sonata 2.0T is poised to make a terrifically strong case for itself. Not a bad achievement for an automaker that's only in its 19th year of manufacturing its powertrains from its own design.
Edmunds attended a manufacturer-sponsored event, to which selected members of the press were invited, to facilitate this report.
