Flat tappets are the old style that don't have rollers on them. There's more friction associated with a flat tappet system and the cam profiles are generally flatter as well. Roller cams have - as the name implies - rollers, which impart less friction, so the cams can therefore have a sharper profile, leading to faster opening and closing events. Zinc (ZDDP to be precice) has a ton of shear-value whcih is critical on metal to metal flat tappent systems.
www.E-tekRestorations.comhttp://E-tekRestorations.blogspot.com/
