Built with thicker castings in crack prone areas, these heads undergo extensive testing and quality control to ensure that you receive the best product possible. ProMaxx performs the following tests and procedures: All fuel rails are drilled and checked, All heads are push rod clearanced, glow plugs and injectors are test fit, all recession depths are checked, all heads are pressure tested, all holes are tapped including glow plug threads and each head gets an in-house valve job. Improved Casting In "Problem Areas". Vehicles with engines built AFTER January 12th, 2006 will use this...