General Motors Co. will sink an additional $20 million into its Bay City, MI, powertrain plant to support production of the auto maker’s next-generation lineup of fuel-efficient Ecotec 4-cyl. engines.

Bay City will produce camshafts for the new engines, which GM will build at its Tonawanda, NY, engine plant. To prepare for the new engines, GM will invest $425 million at Tonawanda for a capacity of 370,000 engines.

The investment in Bay City will create 15 new jobs at the 92-year-old plant.

It is the third investment announcement this year for Bay City, resulting in a total outlay of $62.5 million. The operation also will build connecting rods for the new Ecotecs, as well as connecting rods, camshafts and piston pins for new V-8 program.

Bay City also makes connecting rods and camshafts for GM’s “Family 0” group of engines, which includes the 1.4L 4-cyl. appearing in the new Chevy Volt and Cruze.

The plant produces about 20.2 million engine parts annually.

GM has not provided a timetable for production of the new Ecotec engines, nor has the auto maker released technical details. It says the motors will build upon its current-generation Ecotec architecture featuring gasoline-direct-injection, variable-valve timing and turbocharging technologies.

A 2.4L version of the engine, which currently powers the Chevy Equinox and GMC Terrain Cross/utility vehicles, Buick LaCrosse premium sedan and Buick Regal sports sedan, earned a Ward’s 10 Best Engines nod this year.

GM has said it intends to roll more 4-cyl. engines out across its lineup, replacing less-efficient V-6 motors. For example, the new Regal arriving at dealers now does not offer an engine option larger than 4-cyl.

The strategy reflects an industry downsizing trend ahead of strict new corporate average fuel economy standards of 35.5 mpg (6.6 L/100 km) by 2016.

According to Ward’s data, the penetration of 4-cyl. engines in the U.S. among ’09 model vehicles increased to 61.9% of cars, from prior-year’s 51.7% , while it rose to a record light-truck share of 14.8%. Penetration of V-6 and V-8 engines continued a 5-year decline.