GM announced it will invest $385 million in a new "fuel efficient" engine manufactured in Detroit. Could this be a natural gas enine or line of engines?  Afterall, GM announced a few months ago a joint venture with an Indianapolis based company to design natural gas engines. Perhaps this company already has a design ready to go.

http://www.mlive.com/auto/index.ssf/2011/10/gm_announces_385m_inves...

They are being very quiet about this new engine, only saying it will be very fuel efficient.