VRIS Further Explained.
During times of resonance, the vibrating columns of air (which, though moving, still can support a standing wave) can actually help charge the cylinders. A vibrating column of air has dense sections and rarefied (low pressure) sections. If the standing wave is just right, a dense section of air meets the valve just as it opens. The denser air pours into the port, moreso than if resonance (and thus this standing wave) wasn't happening. The effect is a very mild "supercharging".
But the engine RPM is always changing. If there was only one runner length, there would only be one resonance point. Mazda makes the manifold like a flute that can resonate at several wavelengths by making the runners have variable effective lengths. They do this by using butterfly valves in the manifold to direct air a "long way" or a "short way" (#2 is primarly responsible for this). Closed, the path is "long" and the primary resonance frequency is low. Open, the path is short and the primary resonance frequency is higher. By further changing the frequency in each surge tank (by opening or closing #1 valve, which exposes the each bank to the others' intake pulses, effectively doubling the frequency each surge tank sees), they manage to get several points at which good standing waves are set-up through the RPM band.
In the KL03, the VRIS (variable resonance intake system) plates are controlled by the PCM, which is looking at engine RPM and loading (throttle angle) to know when to open the valves. #1 opens at 3250, which doubles each surge-tanks' frequency. #2 opens at 4250 which then shortens the average path length by 1/2. At 6250, both valves close.
This 6250 point is a bit of a let down. The natural tendency would be to further shorten the path length but the realities of aluminum casting (driven by packaging and cost concerns) rears its head: there's no provision to make things even shorter. The only recourse they have is to revert to the longer path and lower frequency and rely on the 2nd-harmonic to provide a reduced-but-still-effective ram effect. It's a compromise and one of the things I dislike about the KL03 manifold.
The North American I4 does not have this system, just the V6.
BTW, people who get a KLZE but who don't upgrade their PCMs are getting hosed: the KLZE, with it's markedly different manifold, has different resonance points than the KL03. The PCM doesn't know this and switches the valves thinking it's an '03. Meanwhile, the ZE manifold never really has a chance to do its resonance thing properly because the PCM is stupidly flipping the valves at the wrong times.
Also, people who remove or "tie" their VRIS are also hosing themselves. By disabling this feature, they're removing resonance points from the RPM band. Engine torque will suffer in the affected RPM areas and peak power will not climb. (Well, if someone completely removes the #2 valves & shaft, I suppose a bit might be gained from the removal of the restriction in the 4250-6250 range, but it won't be a huge gain and output will suffer everywhere else...)
Its absolutely nothing like VTEC. It IS however, very much like quite a few resonant tuning systems used by nissan, porsche and bmw (to name a few). Adjustable cam timing and resonant air tuning are very very different.
For even geekier info visit http://www.geocities.com/mikey...s.htm