The highest factory rating I believe that Olds published was 390, but like all the other manufactures of the time, that was probably a little short of what it really was. Mine is a 71 model with G heads. In stock form, for the cars, I believe that Olds says that it had 360. However, it is a Hardin rigged motor. Maybe some of the experts could let us know what all Hardin and the others did to these motors. Did they they put different cams etc in them???