The VVT on the ST170 does not "Kick" in, it is progressive so you will not feel it at all. What you should feel is a noticable surge and change in engine note when the inlet manifold runners switch at 5500rpm. If your lacking power after 5500rpm then something is wrong with the inlet manifold runner control or there is a fuel starvation problem, the fuel pumps are weak on the ST170. I would go with a manifold problem.