uses the 1.73 rocker ratio to get the lift, duration. If you buy a NOS Boss 302 camshaft, it is stamped identical to the 289HP solid lifter cam. I have one here in the box. When you use 1.6 rocker arms, it is a 289 cam. I know this will start an argument, but unless Ford screwed up somewhere along the way, I have two of those cams and they are the same. Joe-JDC.