Swirl Control Valve AKA SCV (useful bit of info)

[ghx407]

A lot of people want to delete the secondary butterflies from their intake manifolds, but don't want to go through the trouble.

Just remove the vacuum line from the SCV actuator, and the butterflies will always be fully open. Don't forget to plug the vacuum line.

SCV butterflies are closed only from idle - 2400 RPM. They close using a vacuum signal from a solenoid controlled by the ECU. When RPMs go over 2400, the ECU opens the butterflies simply by closing the solenoid to interrupt vacuum to the SCV actuator. The SCV butterflies are open even when the engine is off because there is no vacuum for the actuator to shut them closed.

(According to Nissan, the purpose of closing the SCVs at low engine speeds was to increase intake air velocity and improve the combustion process at low RPMs. I do not know how much of a performance gain, if any, keeping the SVC butterflies open will produce, but many people claim better performance.)

Lastly, here is a picture taken by Vancouverbc. As you can see, no vacuum = SCV butterflies fully open.

[jeff420]

cool. already knew that as its been posted a few times and plus ive had so many motors apart i knew they stayed open.