|tricks that help their performance. Take a VQ35DE as an example:
1. Continuously varies cam timing. This obviously requires feedback control. The ECU can vary cam timing up to 40 degrees. It can even hold it at 10. It does this by duty cycling the cam timing solenoid.
2. Exhaust cam also has continuous variable valve timing. However, it is phased together with the intake cam. Basically, the main timing chain connects the crank and intake cams together. There are 2 separate chains that connect each intake cam to its respective exhaust cam.
3. The Rev up version had independent CVVT on the exhaust.
The VQ35HR has the exhaust valve timing controlled by an electromagnet.
The VQ37VHR is even more advanced as it can also control lift and duration.
Some great reading here: La-Z-Link
It's not an easy task to add VVT to the exhaust. You need modify the head for oil feeds, build new cams to that can work with VTC, etc. It would likely be far easier to develop a electrically operated timing unit rather than retrofit for hydraulically operated.
As for the intake side, maybe Brett can chime in as he has the detailed knowledge of their inner workings. I'm not sure if it might be a mechanical limitation of the design.