MILFORD, MI – Mash the accelerator of the next-generation Chevrolet Malibu and its front tires chirp with enthusiasm, whisking the midsize sedan down a lonely test track with satisfying doses of V-6 power.

Only there’s no 6-cyl. engine under the shapely hood of the pre-production Malibu “Eco” model we recently drove at the General Motors proving grounds here.

Instead, the surprising burst of torque comes from a stout little 2.4L direct-injection gasoline 4-cyl. backed by the auto maker’s new eAssist mild-hybrid system debuting now as the base powertrain on the ’12 Buick LaCrosse.

Combining old-fashioned internal-combustion technology with an advanced 115V lithium-ion battery pack and 15kW electric motor-generator, the setup provides V-6 grunt in a powertrain that promises 4-banger fuel economy of 26/38 mpg (9.0-6.2 L/100 km) city/highway, according to GM.

Part for part, the systems are identical between the two GM sedans – the difference being the tuning of the motor-generator unit to accommodate varying curb weights. The 2.4L Ecotec I-4 won Ward’s 10 Best Engines honors in 2010.

Drop the accelerator at highway speeds and the ICE and electric motor unite to deliver confidence-inspiring power for passing and merging without the gasp and shrill of many downsized powerplants in bigger cars.

The technology also provides a jolt of electric power when climbing grades, as the LaCrosse with eAssist so ably proved when we tested it in the hills of Northern California three months ago.

Maybe life under the federal government’s new fuel-economy and emissions rules won’t be so bad after all.

With eAssist, the 4-cyl. engine shuts off at idle and restarts after releasing the brake pedal. The transition occurs in a split second and almost without notice.

Some drivers may not even notice the auto-stop feature, which provides the bulk of the fuel-economy gain and emissions reduction. Regenerative braking recharges the battery.

More-attentive drivers likely will detect the subtle restart. It does not occur quite as discreetly as it does on the LaCrosse, and the 4-banger exhibits some raspiness at wide-open throttle.

But in all fairness, the difference probably owes more to the extra noise, vibration harshness damping in the premium Buick model than to any deficiency within the Malibu. Compared with competitive models GM provides on the drive, the Chevy’s cabin is a veritable church pew.

Besides, the eAssist unit portends a more than 15% improvement in highway fuel economy compared with the current-generation Malibu outfitted with a port-injected 2.4L I-4, which GM installed in 70.5% of all ’11 models, according to WardsAuto data.

Compared with the lower-volume V-6 available on current Malibus, the coming Eco model portends a 40% gain in highway fuel economy.

With that sort of capability, what’s a little thrum through the accelerator pedal?

Ride and handling also impress, building off the big strides GM made with the current-generation Malibu released in late 2007 as an ’08 model.

’13 Chevrolet Malibu
Vehicle type front-engine, 4-door, FWD 5-passenger sedan
Engine 2.4L DOHC DI Ecotec all-aluminum I-4
Power (SAE net) 182 hp @ 6,200 rpm
Torque 172 lb.-ft. (233 Nm) @ 4,900 rpm
Compression ratio 11.2:1
Transmission 6-speed automatic
Electric Drive 15 kW belt-driven motor-generator
Battery 115V lithium-ion
Maximum Electric Power 15 hp @ 1,000-2,200 rpm
Wheelbase 107.8 ins. (273.8 cm)
Overall length 191.3 ins. (485.9 cm)
Overall width 73 ins. (185.4 cm)
Overall height 57.6 ins. (146.3 cm)
Curb weight N/A
Price as tested N/A
Fuel economy 26/38 mpg (8-6 L/100 km) est.
Competition Toyota Camry, Honda Accord, Ford Fusion, Hyundai Sonata, Kia Optima, Nissan Altima, Volkswagen Passat
Pros Cons
Excellent driving dynamics I-4 raspy when flogged
Promises high mpg Cargo-stealing battery pack
Cool in-dash storage Base engine arrives late

GM characterizes the Malibu’s chassis control as European-like. We will not go that far, but the new car’s wide stance and independent front and rear suspensions handle the chatter bumps on the auto maker’s test track as well as, or better than, its rival midsize sedans.

Even with low-rolling-resistance Goodyear tires, the Malibu manages to absorb those bumps but still feel grabby – a coup for GM and its tire maker.

Also credit a body structure that’s stiffer overall using mostly high-strength steels, as well as hydraulic ride bushings and isolated lower A-arms.

The rack-mounted electric-power steering system from ZF Group seems well-tuned for a pre-production model, handling a short slalom course with such directness it makes a competitive model seem like a pig on stilts.

One drawback: The battery takes up space in the trunk and eliminates the 60/40 rear-seat split. Pass-through remains on the port side of the rear seats. A family of five might find it too much of a sacrifice.

We’re also curious how the market might accept the eAssist powertrain, which will command a premium price through the first six months until the less-expensive 2.5L 4-cyl. arrives (blame the Malibu’s 6-month pull-ahead).

That means no base LS models until summer. Pricing has not been released for any models.

Like other auto makers in this segment, GM will not offer a V-6 with the Malibu, banking on consumers recognizing eAssist’s superiority. But with a take-rate of less than 10% on the current models, the absence of a V-6 option probably won’t be an issue.

Only the U.S., one of the 100 countries where the new Malibu will be available, will get the Eco model with eAsssist. In Europe and Asia, the Malibu will receive a combination of legacy gasoline and diesel engines, as well as a manual-transmission offering.

The interior also remains a question. The preproduction models provided for testing here are incomplete, making it difficult to judge how well some of the planned upgrades, such as a 2-tier dash and a new molding process meant to make polymers look like leather, will transition from auto show to dealership.

However, the Malibu wins for niftiest storage compartment by making space available behind the touch screen in the center stack.

GM has taken much heat over its past attempts at hybrids. The discontinued Chevy Malibu and Saturn Aura hybrids in the previous decade were assailed as overpriced and underwhelming.

The fullsize trucks employing the auto maker’s 2-Mode hybrid system have been called red herrings by critics, and the Chevy Volt extended-range electric vehicle has been assailed unfairly by conservative commentators.

It would be wrong to include the Malibu Eco in that group. GM has polished an already excellent car to a high shine and proved to critics it indeed has the technology to meet the government’s escalating fuel-economy regulations without leaving consumers wanting.