Professional Products 6.8 Inch Damper for Ford Modular 4.6 Liter V8 features a damper which is the dimensional duplicate of the O.E. damper used on the 2 valve engine. If used on a 4 valve engine, the accessories (alternator, A/C, etc.) will rotate 3 percent slower than stock. Normally this is not a significant amount. This is due to a slightly different diameter of the damper. This damper does not have timing marks on them but do have a notch in the back rim of the damper indicating TDC. This damper represents the most affordable high quality dampers available for this popular engine.