GM discovers another 5 % efficiency improvement in its new 6A transmission.

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.