LA JOLLA, CA – Hyundai Motor America’s meteoric rise from ordinary to outstanding continues with two new variants of its screamingly successful ’11 Sonata sedan.

This year, Sonata sales are up 59.4%, and the car was the 8th best-selling passenger car in the U.S. through September, Ward’s data shows.

The Sonata Hybrid and Turbo driven here are great additions to the Sonata lineup and should move the nameplate further up the ladder, stealing sales from other makes, including the Japanese, whose midsize-sedan lineup is growing stodgy.

Since Ward’s June test drive of the new Sonata variants, Hyundai has tweaked them further as their market launches approach.

Especially impressive in our most-recent test of the Sonata Hybrid is the 55.8 mpg (4.2 L/100 km) we achieved.

Additionally, the Sonata Turbo now is a quieter car than the pre-production model from June, thanks to more insulating material placed between the passenger cabin and engine bay, as well as under the front of the car.

Customer research found excessive engine noise is linked not to power but weakness, Hyundai officials say of the move to lessen the racket.

The Sonata Hybrid, set to go on sale in December, mates a 166-hp 2.4L inline DOHC Atkinson Cycle 4-cyl. with a 30-kW (40-hp) permanent-magnet synchronous motor.

Overall output is 206 hp, higher than that of the competitors, Toyota Camry Hybrid (187 hp), Nissan Altima Hybrid (198 hp) and Ford Fusion Hybrid (191 hp), which all use nickel-metal- hydride batteries.

Hyundai believes its LG Chem Co.-supplied, 270-volt lithium-ion polymer battery is superior, stating advantages over NiMH batteries include 63% greater power density, 13% greater energy density, 12% higher energy efficiency, a 25% longer cycle life and lower volume (44%) and weight (25%).

All that means the Sonata Hybrid’s Li-ion polymer pack should generate less heat, hold a charge longer and its state-of-charge should be better-estimated than for NiMH batteries, Hyundai claims.

Each of the 72 cells that make up the Sonata Hybrid’s battery is encased in a polymer pouch. That, plus the polymer gel electrolyte, is where the controversial “lithium-ion polymer” designation comes from, Hyundai explains.

To give the Sonata Hybrid an atypical better-than-city/highway mpg, Hyundai is using an Active Air Flap system to lessen resistance at highway speeds. Flaps hidden behind upper and lower grilles open automatically at low speeds and with high coolant temperatures, and shut when the inverse is true, reducing the regular Sonata’s 0.25 drag coefficient 10%, Hyundai says.

The electrified Sonata uses a parallel system much like that of other hybrids. It’s able to run solely on battery power at launch and during cruising conditions, relying on the engine during even “gentle” acceleration; regenerative braking occurs during deceleration.

The car’s braking, as noted in June, is as close to “normal” as possible, lacking the grabby-ness of other hybrid’s brakes.

The Sonata Hybrid’s standard 6-speed automatic shifts differently from most hybrids, which rely on continuously variable transmissions. Hyundai’s use of the 6AT is smart, based on research showing consumers prefer step-gear automatics to CVTs. Plus, the off-the-shelf, in-house technology saves money.

Ward’s finds the 2.4L gas engine kicks on at around 20 mph (32 km/h), about the same speed at which most other parallel hybrid’s engines spring to life. Hyundai says staying in EV mode is possible up to 62 mph (100 km/h), but we found that difficult, even on flat surfaces and with a half-full battery.

’11 Hyundai Sonata Hybrid
Vehicle type Front-engine, front-wheel-drive, 4-door sedan
Engine 2.4L DOHC 4-cyl. with aluminum block, head
Power (SAE net) 206 hp @ 6,000 rpm (electric motor 40 hp)
Torque 193 lb.-ft (262 Nm)
Transmission 6-speed automatic
Wheelbase 110.0 ins. (279 cm)
Overall length 189.8 ins. (482 cm)
Overall width 72.2 ins. (183 cm)
Overall height 57.7 ins. (147 cm)
Curb weight 3,618 lbs./1,641 kg
Base price TBA
Fuel economy 36/40 mpg (6.5-5.9 L/100 km)
Competition Toyota Camry Hybrid, Ford Fusion Hybrid, Nissan Altima Hybrid
Pros Cons
Slick black grille Askew interior trim
40 mpg highway EV mode temperamental
No grabby brakes Weird vibration at stop

A good chunk of our afternoon drive in the Sonata Hybrid was in EV mode thanks to a mountain descent, coasting at speeds as high as 80 mph (129 km/h).

Fuel economy reached the impressive (for a 3,618-lb. [1,641-kg] sedan) 55.8 mpg during the downhill coasting. But we ended the day at an average 40.4 mpg (5.8 L/100 km) after stop-and-go city driving and some uphill highway stretches.

In a fuel-economy challenge, the winning team managed a road-rage-inviting 60.4 mpg (3.9 L/100 km) at an average speed of 30 mph (48 km/h).

One issue: Our pre-production tester experienced strange, strong vibrations coming to a stop. Officials suspect a regenerative-braking issue was at play and are investigating.

On the road, the Sonata Hybrid handles much like the regular Sonata in that it is a middling performer: not transmitting too much – but also not totally isolating – road irregularities into the cabin. The car remains fairly flat in curves, and steering is neither too light nor heavy.

The Sonata Turbo, or 2.0T for short and on sale now, is another animal entirely. Taking the place of a conventional V-6 in Hyundai’s midsize sedan lineup, the Turbo variant is designed for fun rather than fuel efficiency.

Still, we returned a respectable 34.3 mpg (6.9 L/100 km) at an average speed of 50 mph (80 km/h) over 53.6 miles (86.3 km) of mostly 2-lane undulating roads.

During our route, the Sonata Turbo tester’s Active Eco button was engaged. The function allows for smoother initial acceleration, maintains a more constant vehicle speed during cruising and “curbs excessive acceleration,” Hyundai says, adding a 7% improvement in fuel economy is attainable.

Fuel economy for the Sonata 2.0T is rated at 22/33 (10.7-7.1 L/100 km) city/highway.

The 2.0L turbocharged direct-injection I-4 with dual variable valve timing makes 274 hp at 6,000 rpm and 269 lb.-ft. (365 Nm) of torque.

Those specs best the V-6 Camry, Altima, Fusion, Honda Accord and Chevy Malibu, as well as the new turbocharged 220-hp 2.0L Buick Regal.

Hyundai touts its use of a twin-scroll turbocharger, which boosts torque with a split-wall design between the exhaust paths. The patented air-guiding duct lowers the intercooler outlet temp 50º F (10 º C), improving torque and fuel-efficiency, the auto maker says.

The Sonata Turbo tested has a crisper on-road feel than the base Sonata, which is sometimes floaty. Steering also is heavier than that of the base model, appropriate for a performance variant.

Gear shifts with the car’s standard 6-speed automatic transmission are softer than might be expected. Then again, this car will duel with the current midsize V-6 contingent, not known for their sporty nature.

Shifting via paddles is fun, and necessary, to boost torque at lower cruising speeds. It isn’t easy to deduce the car’s turbocharged disposition unless mashing the accelerator.

The noise-reduction improvements, as well as excellent fuel economy, should prod V-6 loyalists to embrace the 2.0T. With coming fuel-economy rules, they may not have a choice as sixes likely will dwindle.

The Sonata Hybrid’s unique exterior is a winner, with less ornamentation than the chrome-laden regular and 2.0T models. With a blacked-out lower grille and stubby nose, the car is attractive and immediately identifiable as a hybrid Sonata. The Sonata Turbo, on the other hand, is virtually identical to the regular Sonata.

A wine-leather interior will be offered on the 2.0T’s Limited trim, $27,045 to start. A $24,145 SE grade also is available. Adding option packages tacks on more than $2,000.

The Sonata Hybrid interior inspected here has good fit-and-finish, although a B-pillar trim piece doesn’t meet cleanly. Seating comfort is above average, with extra soft rear seats.

Really cool is the Sonata Hybrid’s human machine interfaces, namely the 4.2-in. (10.7-cm) liquid crystal display trip computer between the tachometer and speedometer, with vivid color and crisp definition. The premium package adds a Hybrid Technology Display screen on the center stack, showing energy flow.

Overall, the success of the regular Sonata is bound to rub off on the two variants.

Hybrid pricing hasn’t been announced, but if Hyundai’s grade strategy is any indication it should sell well. The Sonata Hybrid will match the equipment of the regular Sonata’s GLS grade, $19,195 to start, plus add some higher-end features.

If Hyundai can price the Sonata Hybrid under $25,000, it will have a hot-seller on its hands.