SR20DET VVT questions

[lessthanjakejohn]

Someone brought this up at another forum and I'd thought I'd ask you guys.

What would happen if you took the VVT Cams out of S14 and S15 motors and replaced it with another cam?

Also, is it possible to disable VVT?

PS: Can someone lead me to a site that explains Nissan's VVT

[lessthanjakejohn]

Quothe ItzGenXVVT - Continuous Intake Valve Timing. There is nothing special about this that there is to talk about. The reason for the VVT is because of the Low Intake port design used for the S14 and later SR20DETs. The Low Intake Port design is a shorter distance to the valves from the intake manifold, but must curve and go around the lifter supports. This in turn leads to less breathing due to the turbulence the intake air must go through before hitting the back of the valve. Also, being a Low Intake port design, the port literally can not contour to enter the cylinder at a good angle (and thus VVT to hold duration slighly longer to capture more air). The S13 high port design was literally a straight even path with light curvatures to get into the combustion chamber. The even amount of airflow and a good angle to enter the combustion chamber didn't need this VVT to get the even power as the S14 generation (S15 is stronger because of the turbo). Not only did the S13 motor match that of a S14, but it did everything the S14 could at a lower RPM. The change was made between the S13 and S14 motors because of the emissions standards from that of a long port. It was believed that a longer port had less "control" over emissions because of the length the air had to travel into the engine would be "delayed". With all that in mind, would you want to pay 1000 extra for something you didn't want? I personally like the High Port design of the S13 and don't need any of that other fancy stuff they changed. S13 SR20s also respond better to upgrades because of the port design takes it so well, especially turbo upgrades. Before I knew anything about the S14 and later motors, I thought they were the one to go with and the one I wanted, with a little bit of research and long chats with the Australians, you learn that VVT was sort of a cover up for Nissan having to change the port designs.

[ItzGenX]

[GodzillaFan]

anytime aftermarket cams are used, the VVT is disabled.

its not "Continuous" either, there are just 2 settings

it comes on at ~1300 rpm, shuts off at ~5400 rpm

Continuous Valve Timing is used in the VQ35DE.

[ItzGenX]

It is continuous. Many would say it goes "off" from those ranges because they don't "feel" it anymore. The reason being is because some points it will retard the cam timing instead of advance. The VQ35 cam timings are continually advanced most of the ranges because its a NA motor and ultimately benefits from it. A turbo motor thrives off the boost and can only benefit so much from cam advancements for torque and high end power. The VVT on SR20's have a set adjustment throughout the rpm range whether advancing or retarding without any real input sensors to become totally variable. The VQ35 detects engine load, knock, and rpm for the right adjustments during the situation making it almost infinitely variable.

[yellaspecV]

why would you disable VVT w/ aftermarket cams? All VVT does is hold the valve open longer... w/ a higher lift cam this would make the VVT even better!!

[ItzGenX]

Depends what kind of aftermarket cams you get. Regular Stage 1 cams will still allow vvt to work, but too high of a duration will flood the cylinder in a way. It will also cause too much valve overlap and the effeciency will begin to fall off.

[cIvIcKILLA240style]

anytime aftermarket cams are used, the VVT is disabled.

its not "Continuous" either, there are just 2 settings

it comes on at ~1300 rpm, shuts off at ~5400 rpm

Continuous Valve Timing is used in the VQ35DE.

not true....you can use aftermarket cams with the VVT enabled. As much research i have done on this subject I found out the the VVT is manipulated by the ECU from the inputs of the VSS, TPS and MAFS. starting from idle the VVt holds the cam at 22 degrees retardation(har har har) and depending on the inputs of those three sensors is what governs the actions of the VVT. I have been researching this for quite some time now and this is what I was able to learn fro the FSM and other experiances. If anyone has any conflicting information on this please let me know.....

J