General Motors Corp. and Japan's Isuzu Motors Ltd. are forming a $320 million joint venture to build new-generation diesel engines for GM trucks at a new factory outside Dayton, Ohio. The new, high-tech V-8 engines to be made at the plant, which use direct-injection technology, offer "very significant" reductions in noise and emissions and better performance and fuel economy than the traditional diesel engines GM now offers in its full-size pick up trucks.