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Variable Cam Control Tuning: Why Variable Cam Control?

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Why Variable Cam Control?


00:00 - Like most things, when it comes to engines, the timing of the valve opening and closing events is something of a compromise.
00:07 By adjusting the cam timing, we can take advantage of the air speed and inertia to optimise the cylinder filling.
00:13 The problem with this is that the cam timing that's optimal at low RPM will almost certainly not be ideal at high RPM and vice versa.
00:23 Hence some kind of compromise on performance needs to be accepted.
00:27 While our aims in the aftermarket world are often centred around performance where we want to eek out every last kilowatt from each engine, it may come as a surprise to realise that the OE manufacturer usually has a vastly different set of goals and managing emissions and optimising fuel economy will almost certainly come much further up the list than outright power.
00:50 Interestingly though, cam timing also plays a role in both of these metrics too.
00:55 As time has marched on, OE manufacturers have needed to develop more tricks to get their engines to produce good power, a wide torque curve and low emissions all while drinking less and less fuel.
01:07 Considering the impact cam timing has on all of these parameters, it's probably not a surprise that these manufacturers have developed techniques that allow the cam timing to be varied while the engined was running.
01:20 As discussed already, the early systems consisted of a simple switched cam timing system where the intake cam could be swung back and forth between full advance and full retard based on RPM which proved to be effective to a point.
01:34 The real advantage though comes from full continuously variable cam control systems where the cam timing can be set to track a target angle which can be adjusted based on both load and RPM.
01:47 These systems use engine oil pressure to move the cams incredibly quickly and when calibrated properly, they can offer lightning fast and pin point accurate control, allowing the exact cam timing to be optimised for each combination of load and RPM, ensuring maximum performance from the engine.
02:06 Interestingly, earlier in my career when continously variable cam control was just starting to become commonplace on performance engines, many of the aftermarket standalone ECUs available hadn't developed the necessary control technology to control these systems.
02:22 At the time I remember many mainstream tuners as well as ECU manufacturers claim than cam control was a gimmick and wasn't necessary.
02:31 Since this was a popular belief that I still hear from time to time, let's dispel this myth.
02:37 As we can see from this dyno graph, there is no gimmick.
02:41 This shows the difference in power and torque from our turbocharged Subaru FA20 engine with the cam timing fixed compared to a fully functional cam control system that has been properly optimised.
02:53 You can see that the peak power number hasn't really been affected because of the natural cam timing position which tends to favour high RPM performance.
03:02 What we can see though is just how much more low to mid range torque and power we gain from cam control systems such as this, as well as how much quicker the turbocharger reaches full boost.
03:14 It is worth mentioning that cam control isn't right for every application though and there are some times when locking out the cam control in favour of fixed cam timing is absolutely the correct move.
03:26 This usually involved very high specific output engines where very aggressive cams are required.
03:33 When we fit very large cam profiles this severely restricts the amount of cam movement we can utilise before we run into contact, reducing the usefulness of the system in the first place.
03:45 The other application where variable cam timing is less valuable is in engines that only operate over a very narrow rev range.
03:52 Since the aim of continuously variable cam control is to provide a wide powerband this becomes less relevant if we're only using perhaps 1500 to 2000 RPM of the rev range right up near the rev limiter.