Nissan's variable valve timing control...

 

http://forums.maxima.org/showthread.php?t=262261

NVCS gives even more advantage on the TT too. At high load/revs, exhaust back pressure is higher than intake pressure so you don't want as much overlap - you get better cylinder filling by retarding the intake valve timing. Bigger turbos and better manifolds mean you can increase the point at which the intake timing retarding occurs due to lower exhaust back pressure. Most off the shelf chips I've seen don't change the VTC switching point, although it will vary massively from car to car depending on mods...

I've had the cams for the VH45 ground 70/30 30/70 @ 50 thou then installed the intake 20deg retarded. Means with it on cams run to spec, with it off there is less overlap for low speed performance.