Nissan’s 370Z VQ37VHR Cylinder Head and VVEL Continually Variable Cam Timing Technology, Technological Terror or Performance Breakthrough?

This is all great high tech stuff but it comes at a price. For us tuners, the valvetrain is going to be difficult to improve and is far beyond the present capabilities of the aftermarket to modify. Even Nissans factory service manual states that the valvetrain is unserviceable and that the only repair that can be done is to replace the whole head! This means no cams and no way to easily port or modify the head. The only easy performance solutions are either forced induction or to swap the heads for an earlier version of the VQ. We suspect this is why this technology was left off of the uber performance flagship Skyline GTR’s VR38DETT engine.

To be able to change the intake valve motion on the fly, the VVEL system relies on a staggering array of moving parts, two rotating shafts, a rotating eccentric, a rocker shoe and a link arm with an adjustable fulcrum

The VVEL system is exceeding complex. It has a lot of moving parts creating a bunch of complexity. All of this makes a valvetrain that is exceedingly difficult to work on. Nissan considers the system a sealed non serviceable disposable part. All of this monkey motion also has a lot of friction although other positive attributes of the system cancel this out. The reciprocating action of the valve actuating rocker has a hard time maintaining a hydrodynamic wedge of oil on its rubbing surfaces and thusly it relies on Nissan’s low hydrogen DLC coating with ester super oil to operate with low friction and noise.

Read more about this issue in detail here;

http://www.370z.com/MagazineArticles/tabid/57/articleType/ArticleView/articleId/55/Oil-Temps-engine-rattles-300-oil-Diff-temps-and-other-issues-The-Truth.aspx

The easiest first step for performance tuning the VVEL might be ECU tuning of the VVEL system to bias its mapping toward performance instead of being compromised by emissions and fuel economy issues. The difficulty here is that the VVEL system is controlled by an ECU independent of the engine’s ECU. So the code architecture is nothing like what is previously experienced by tuners who have decoded the Nissan ECU. This will be like starting all over as far as ECU tuning and may take awhile.

Here is the fulcrum for the rocker of the VQ37VHR VVEL system.  The adjusting screw and lock nut are visible on the top of the rocker link.

An allen wrench is used to turn the adjusting screw while the locknut is held with a box end wrench

A close up of the magic screw and the fulcrum out of the rocker link

The fulcrum adjusted to the low position

The fulcrum adjusted to the high position.  This gives full race cam lift and duration numbers!

The amount of duration and lift can also be increased by turning the systems magic screws. What is the magic screw? It’s a screw that adjusts the neutral position of each individual moveable fulcrum. The screw is there to help reduce assembly variables of the system when it is put together at the factory. This way valve clearance can be controlled with just select fit cam followers just like in a conventional valvetrain. Without the magic screw, you would have to worry about the tolerance of every single part of the VVEL system. When the screws are turned to the limit of its adjustment, the intake valves can experience a true race cam like 300 plus degrees of duration and 0.505 inches of lift.  This is pretty awesome considering that the stock maximum position is around 280 degrees of duration and 0.450 lift, about what an aggressive street cam would be.

Here is the VVEL systems plotted lift and duration at various degrees of rotation of the systems stepper motor controlled eccentric shaft .  The highest black line is the impressive race cam like specs in valve motion that can be obtained with the magic screw turned to the limit of travel

Sounds easy right? Not exactly, although valve spring tension and coil bind are not a problem, finding the screws base adjustment is. To set the magic screw correctly, a high precision fixture must be built so all of the screws can be adjusted to the same installed position after all the parts are assembled taking the manufacturing tolerance of the parts in the system out of the equation. This way valve lash can be solely controlled by the select fit cam followers just like the older VQ motors. Jim Wolf Technology is currently investigating this possibility of re-adjusting the screw using a fixture. More aggressive ECU tuning of the intake valve events coupled with adjusting the magic screw will probably take care of the intake side of things. What can be done for the exhaust side?