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Variable Cam Control Tuning: Switched vs Continuous Cam Control

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Switched vs Continuous Cam Control

03.48

00:00 - With specific regard to valve timing, one of the first techniques employed by manufacturers in search of improved performance and wider torque curve was the use of switched cam timing systems.
00:11 There's a variety of systems that fall into this category like Nissan's VTC or NVCS that was used on several engines in its RB and SR range.
00:21 Or Toyota's VVT that was applied to its black top 20 valve 4AGE.
00:26 In essence these systems are very similar to a proper continuously variable controlled system however they only operate in one of 2 positions, either full advanced or fully retarded.
00:38 As part of this strategy, the range of cam movement is also usually much more limited than a continuously variable cam control system.
00:45 As we touched on earlier, this style of cam control is also typically only applied to the intake cam due to it having a much more drastic effect on engine performance compared to the exhaust.
00:57 The control of a switched cam system like this is still achieved with engine oil via an ECU controlled solenoid, however this time the solenoid is not pulse width modulated and instead it's either in the on or the off position and the ECU will have a simple table that defines an RPM point where the solenoid will switch from one state to the other.
01:17 There can also be benefits in making this switching point 3D by adding engine load or throttle position as a separate axis.
01:25 In some instances, you may find that the cam timing will switch states twice as you transition through the rev range and this is common in particular with Nissan's implementation where the system will typically switch on at low RPM such as 1500 then switch off again at higher RPM of perhaps 6000 to 6500.
01:45 While not strictly the same strategy we're also going to cover systems such as Honda's VTEC and Nissan's VVL in this module.
01:54 To avoid confusion, Nissan's VVL is quite different to their earlier VTC system.
02:00 These systems use 3 cam lobes on each cylinder with a small cam lobe where the lift, duration and timing are optimised for low RPM performance as well as a larger cam lobe which optimises the valve timing and lift for high RPM performance with the ability to switch between lobes on the fly.
02:20 These systems were a game changer when they were first introduced and really did an excellent job of reducing the inherent cam choice compromises and providing the best of both worlds.
02:31 They're also oil pressure controlled and the control strategy and the tuning process are really identical to a switch cam timing system which is why we're discussing them here.
02:41 In more recent engines, Honda chose to embrace continuously variable cam control and add this to their existing switched cam system with their iVTEC system used to great effect on their popular K20 engine.
02:55 This is really the ultimate iteration of this sort of technology in my opinion because it allows the cam timing as well as the valve lift and duration to be optimised throughout the rev range.
03:05 While being able to move the cam timing while the engine is running is a very powerful technique, the reality is that the cam profile itself is still a compromise between low and high RPM performance.
03:17 Anyone who's tried to daily drive a car that's fitted with an aggressive race only style cam with a lot of overlap and duration will know the compromise that I'm talking about here.
03:28 Low RPM drivability is usually terrible not to mention fuel economy and while adjusting the cam timing can help, there's only so much that you can expect here.