It's only been a year since General Motors launched its 6T40 six-speed automatic transmission for mid-size and compact cars. When it was introduced, this new transmission brought with it a five percent bump in fuel efficiency. The engineers at GM Powertrain are now developing a second generation variant of the 6T40 for introduction in 2011 that will bump fuel efficiency by yet another five percent.

The new version will have updated electronic control strategies based on the work done for the new 2011 Chevy Equinox with the four-cylinder engine. The Equinox manages a 32 mpg highway rating. These new controls developed for the Equinox will contribute three percent of the improvement for 2012 models like the Cruze compact.

Another two percent improvement will come from refinements to the guts of the transmission. Changes to the hydraulic valve body, friction plates and variable flow solenoid will cut internal pumping losses and friction.

GM is also working on its own in-house developed dual clutch transmissions. GMPT is developing a dry clutch system that should yield another incremental improvement in efficiency, but no announcement was forthcoming about timing.

A twin-clutch gearbox, double clutch transmission or dual clutch transmission (DCT) is a semi-automatic transmission with separate clutches for odd and even gears. The outer clutch drives the odd numbered gears, while the inner clutch drives the even numbered gears. Shifts can be accomplished without interrupting power, by applying the engine's torque to one clutch just as the engine's torque is being disconnected from the other clutch. Since the synchronizers that select an odd gear can be moved while driving the car in an even gear, and vice versa, DCTs have been configured which shift more quickly than Formula One and other cars equipped with single-clutch AMTs (automated-manual transmissions, a.k.a. single-clutch semi-automatics). Also, with a DCT, shifts can be made more smoothly than with an AMT, making a DCT more suitable for street-driving.[1]

A twin-clutch gearbox eliminates the torque converter used in traditional automatic transmissions. Instead, dual clutch transmissions that are currently on the market use wet multi-plate clutches, similar to the clutches used in traditional automatic transmissions

**Most production cars have a wet sump oil system. The HowStuffWorks article on car engines shows you where the sump is -- it's the area below the crank shaft. In a wet sump, the oil that you put into the engine is stored beneath the crankshaft in the oil pan. This pan has to be large and deep enough to hold four to six quarts of oil -- think about two 3-liter bottles of soda and you can see that this storage area is pretty big.

In a wet sump, the oil pump sucks oil from the bottom of the oil pan through a tube, and then pumps it to the rest of the engine.

In a dry sump, extra oil is stored in a tank outside the engine rather than in the oil pan. There are at least two oil pumps in a dry sump -- one pulls oil from the sump and sends it to the tank, and the other takes oil from the tank and sends it to lubricate the engine. The minimum amount of oil possible remains in the engine.

Dry sump systems have several important advantages over wet sumps:

Because a dry sump does not need to have an oil pan big enough to hold the oil under the engine, the main mass of the engine can be placed lower in the vehicle. This helps lower the center of gravity and can also help aerodynamics (by allowing a lower hoodline).

The oil capacity of a dry sump can be as big as you want. The tank holding the oil can be placed anywhere on the vehicle.

In a wet sump, turning, braking and acceleration can cause the oil to pool on* one side of the engine. This sloshing can dip the crankshaft into the oil as it turns or uncover the pump's pick-up tube.

Excess oil around the crankshaft in a wet sump can get on the shaft and cut horsepower. Some people claim improvements of as much as 15 horsepower by switching to a dry sump.
The disadvantage of the dry sump is the increased weight, complexity and cost from the extra pump and the tank -- but that's a small price to pay for such big benefits!