The following link will take you to a series of engine articles written by Bruce Mallinson, the engine guy at Diesel Injection of Pittsburgh. They are well know for their work on various engines, and he is specifically a Cummins specialist. On the left side of the site, click on "Bruces Hp and Torque articles"
*edit* Link is no longer valid. Diesel Injection of Pittsburgh now located at http://www.pittsburghpower.com/