With 1 7/8 you shouldnt have any problems.. you might want to run 1 7/8 but with a 3.5" collector.. will make more torque.. I'm running 1 7/8 with a 3.5" collector on my 416... It does go back down to a 3" after the collector but I also run electric dumps right after the collector to help reduce back pressure EDIT this is with a full exhaust out to the bumper