Two top Volkswagen engineers who found they couldn’t deliver as promised a clean diesel engine for the U.S. market are at the center of a company probe into the installation of engine software designed to fool regulators, according to people familiar with the matter.

The two men, Ulrich Hackenberg, Audi ’s chief engineer, and Wolfgang Hatz, developer of Porsche’s winning Formula One engines, were among the engineers suspended in the investigation of the emissions cheating scandal that sank the company’s market value by 43% since Sept. 18 and triggered a world-wide recall to refit the engines to meet clear-air standards, these people said.

Messrs. Hackenberg and Hatz, who didn’t respond to requests for comment, are viewed as two of the best and brightest engineers in German industry. They were put in charge of research and development at the Volkswagen group shortly after Martin Winterkorn became chief executive in January 2007. Mr. Winterkorn, who resigned over the scandal, couldn’t be reached for comment. Details