General Motors Co. will invest nearly $378 million to upgrade six of its manufacturing sites to produce more fuel-efficient engines and transmissions.

GM officials said plants in Flint and Bay City, Mich.; Toledo, Ohio, and Bedford, Ind. will support production of a new Ecotec small gas engine, a new V6 engine, 8-speed transmission, and tooling for an existing 6-speed transmission. The automaker said it is also increasing previously announced powertrain investment in plants in Romulus and Saginaw, Mich., to $646 million, an increase of $46 million, to support production of the new V6 engine. Combined, the two investments will retain about 1,650 jobs at the six facilities.

“We are investing in technologies and manufacturing capabilities that produce high-quality, fuel-efficient vehicles and components for our customers,” said Diana Tremblay, vice president of GM North American Manufacturing. “Today’s announcement demonstrates GM’s commitment to growing the business and strengthening the plant communities where we receive so much support.”

“The selection of these plants and the opportunity for the United Auto Workers to build the next generation of engines and transmissions reflects the great efforts of our workforce,” said UAW Vice President Joe Ashton, who directs the union’s GM department. “This investment goes a long way to ensuring GM remains a marketplace leader and our members can continue to support and share in the company’s growth.”

GM’s newly announced $331.8 million investment includes:

• $215 million in Flint Engine Operations for a new small Ecotec gasoline engine, which is part of a new family of engines that includes 3- and 4-cylinder variants with displacements ranging from 1.0 to 1.5 liters. Details of what variants the plant will build will be announced later. The plant will also upgrade tooling for its current V6 engine.
• $55.7 million in Toledo Transmission Operations for increased capacity and tooling to produce an all-new, advanced 8-speed automatic transmission and an existing 6-speed transmission. The Toledo-based 8-speed will be used in numerous GM vehicles by the end of 2016.
• $31.7 million in Bay City Powertrain including $19.2 million to produce components for a new V6 engine and $12.5 million to produce components for the small Ecotec gasoline engine.
• $29.4 million in Bedford Castings including $19 million to produce components for the small gas engine and $10.4 million to produce components for the new 8-speed and existing 6-speed transmissions.

The additional $46 million brings the total to $646 million for the V6 project including:

• A $41 million increase to $256 million for Saginaw Metal Castings Operations to produce castings for the new V6 engine.
• A $5 million increase to $390 million for Romulus Engine Operations to build the new V6 engines.