Some manufactures do use a single cam concept for variable valve timing.

A 2nd lobe for a single valve is normally deactivated- allowing the normal torque response at low RPMs. At high RPMs this 2nd lobe is activated hydraulicly to open this valve at a different timing configuration. This is accomplished through the lifter. Very similar in concept to the DC HEMI that deactivates cylinders to increase fuel mileage. This is also contolled by lifters that can be activated or deactivated.


So there you have it- VVT can be accomplished with DOHC/SOHC/cam in block/No cam at all.