Continuously Variable Valve Timing Control System

Does it have anything to do with infinite variability?

Feel free to add anything else about it.

 

its like VTEC and VVT-i systems for Honda and Toyota systems, respectively

just adjusts timing so your engine is efficient under load.

as far as infinite variablility, thats perspective... timing will constantly change based on engine rpm and load....

 

My sentiments exactly. Nissan needed a known 'abbreviation' in acclaim to its engine's power derivative.

 

Can I get a better explanation besides "its kinda like vtec". So if it is like hondas overrated vtec, that means theres another intake cam with its own rocker arm that attaches itself to the other cams at about 5000-6000 to open the valve longer? Im sure its not exactly the same as honda's vtec. So whats the difference?

 

Let me give you a simple example that may not apply to the Z. It is just a general example.

Under hard accelleration, it is normally helpful to have the exhaust valve and intake valve open at the same time for a split second. This helps to blow out more of the burnt air. However it wastes some good gas/air and is not all that efficient.

If you are just cruising down the highway, you only need enough power to keep you moving. In this case, the valve overlap for exhaust scavaging is not needed.

So, CVTCS or other variable timing systems can vary the timing to adjust when the valves open. At one moment they could allow both valves to open for power, and at the next only one at a time for efficiency.

I think this makes sense and is a valid example. Although, I do not know if the Z can support this exact example.

At one time I thought that variable timing would allow the cams to actually lower to push the valves open further. For example, when revs increase, the torque on the timing chain would pull on the spring-loaded cams and lower them, thus opening the valves further. I really don't think this is how it works though, but it would be cool. Unfortunately, if the cams lowered, the valves would open further, but maybe not shut all the way.

 

From what I understand it is nothing like vtec. Vtec Is the third cam lobe that locks into place at a certain rpm to allow higher and longer lift and duration at higher rpms. Its actually like having 2 sets of cams. Low rpm and high rpm. Nissans version just adjust timing on the cams. the amount of over lap between the intake and exhaust cams.

 

From what I understand it is nothing like vtec. Vtec Is the third cam lobe that locks into place at a certain rpm to allow higher and longer lift and duration at higher rpms. Its actually like having 2 sets of cams. Low rpm and high rpm. Nissans version just adjust timing on the cams. the amount of over lap between the intake and exhaust cams.

 

It is an adjustable cam gear driven by its own motor on the intake cam. There is a chain attached to this gear that connects it to the exhaust cam gear. This allows the motor to adjust the timing on both intake and exhaust, as opposed to the exhaust being driven by the main timing chain. The main timing chain connects to the intake cam gears only, which is also connected to the adjustable cam gears via the motor. This allows the ECU to vary the timing "on the fly" by advancing or retarding the adjustable gears postion relative to the timing chain position. Since the adjustable gear is also connected to the exhaust cam gear, this also is adjusted. VTEC is hardly overrated, as it allows multiple cam profiles to be used on an engine. iVTEC is the same system but with variable timing incorporated. Nissan has a similiar system on the SR20VE known as VVL, or Variable Valve Lift. Both systems use a seperate "dead lobe" on the cam that has its own follower that rotates independently of the valvetrain. When a preset RPM is reached, the follower "locks" into the valvetrain assembly were the lower cam followers are, driving the entire assembly by the larger high-rpm cam. The VQ35 lacks such a system.

 

Does anyone know of a diagram, and/or operating system description, so we can really understand this system? I have the maintenance manual on CD, and it doesn't contain this kind of detail either.