The Union of Concerned Scientists (UCS) have both praised and condemned two of the latest hybrid offerings. The UCS auto engineers feel the BMW ActiveHybrid X6, a 'muscle hybrid', squanders its hybrid drivetrain by boosting power.
At the same time, the Mercedes-Benz S400 is seen as partially successful. It lowers cost, but uses a 'relatively weak' hybrid drivetrain along with a downsized conventional gasoline engine, to increase fuel efficiency.
The UCS updated their Hybrid Scorecard to reflect their findings.
|BMW ActiveHybrid X6|
UCS points out BMW has added on to an already powerful eight cylinder engine to boost the X6 to the highest horsepower and torque of any hybrid on the market. And so the hybrid X6 has become the worst performer, from an environmental perspective, than the Lexus RX 450h. The RX450h has a 7.4 rating on the UCS Scorecard, while the X6 was given a 4.4.
The UCS also notes the X6 ActiveHybrid comes with $10,000 of 'forced features', including a deluxe sound system and other features not included in the base model. The UCS feels that unnecessary features drive up the cost of hybrid cars.
|S400 Hybrid from Mercedes-Benz|
The first hybrid from Mercedes-Benz, on the other hand, took and eight cylinder engine and replaced it with a six-cylinder hybrid. That improved the costs and made for higher fuel economy. And for the first time for a hybrid, the S400 hybrid actually costs less than the base mode S550.
The S400 Hybrid is a mild hybrid, incapable of driving on electric power alone. But it does come with start-stop technology and regenerative braking. It's also the first production hybrid to use lithium-ion batteries. The S400 comes with no forced features.
The UCS engineers gave the S400 a score of 5.3 on their scorecard, but not the hybrid value is 'very high.' In other words, the environmental 'bang for your buck' or cost effectiveness of the S400 Hybrid is very high in achieving its environmental performance.