![]() ![]() Compared to what the people at BMW came up with, Nissan claims a 32-percent quicker response because of VVEL, 52-percent less parts per cylinder, and a 20-percent smaller design overall. If it sounds complicated, that's because it is. Output cam movement is varied through a rotating control shaft inside a small, electric motor this effectively alters the rocker arm links' fulcrums for constant valve lift adjustment. ![]() The rocker arm imparts its motion onto an eccentric cam mounted on a small, rotating driveshaft to make all of this happen. Here, an unconventional-looking rocker arm paired with two special links is responsible for moving the intake valves. At higher engine speeds the system allows the valves to open farther and for longer periods of time where the likelihood of blowback is reduced because of increased air velocity this results in more top-end horsepower, or, the stuff that makes us care about VVEL in the first place. ![]() This reduces the chance of the air/fuel mixture blowing back the wrong way, which results in a more complete burn and, ultimately, more torque. Like other manufacturers' variable valve timing systems, VVEL keeps the intake valves open for a shorter period of time during moderate driving conditions. VVEL controls the incoming charge at the intake valves, and Nissan's existing CVTCS (Continuously Variable Valve Timing Control System) manages each of the valves' up and down characteristics, specifically lift and duration. Unlike VTEC, Nissan's system focuses on low- and medium-speed characteristics-not so much on top-end power. As load increases, the system once again switches off, which allows the valves to open later and take advantage of the higher rate of air that's moving in. At higher engine speeds, valve timing advances to help retain an appropriate volumetric efficiency, which, in other words, means torque can be preserved or increased. At lower engine speeds, the system remains closed, leaving intake valve timing retarded for smooth idling and drivability. Depending on the engine, look for VCT on the intake side only or on both cams. Valve lift and duration don't change here, like with VTEC, but none of that takes away from VCT's effectiveness, especially by 1987's standards. It begins with the ECU telling an electric solenoid to turn on, which directs a high-pressure oil stream through the cam and into a slave mechanism that ultimately changes the relationship between the cam and its gear. Also known as NVCS (Nissan Valve Timing Control System) in some circles, here, duly equipped cams can be advanced or retarded relative to their gears. ![]()
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