'cuz the material for a roller cam can't be the same cast iron used for FT cams.... it won't survive with the rollers' very high and concentrated contact pressures. So that eliminates a cast-in iron gear on the cam that is compatible with the stock shaft gear.
I guess my point is why don't they make the roller cams out of the same material the factory roller cams are made out of and then we can just use our factory gear drives/shaft like we've been doing for 60 years with all the LA's?
