Good points Tristan but don't forget the other methods like TVIS/VVT(l)i. These systems are basically the same but provide a lot more smoother torque band. TVIS is the older system and basically it's a set of butterflys in the inlet manifold which can be closed or open, depending on vacuüm in the inlet manifold. If closed, only 4 inlet ports are open and that creates higher air speed for more torque. At 4400rpm a vacuüm solenoid sends a signal to the ecu and then the butterflys will open the remaining 4 inlet ports. Cylinderhead will have to do it's work up from here. This systeem feels much like VTEC, but it operates very different.
VVT(Li) is much much more complicated and it uses way more signals from the ecu such as
- engine rpm
- TPS signal
- Inlet vacuüm
- Coolant temp.
Based on these signals it can operate from 0rpm upto the revlimiter and so it changes constantly. Toyota has mapped these ecu's in such way that it operates much like a VTEC, you also get that agressive switch @ 6000rpm but of course with a standalone ecu there is not much a man can't do
I have to say I really respect these engines and their systems. Let's not forget systems like the first VTEC and especially TVIS are very old (1984) and they developed both systems in a great way providing fun, high rpm's and torque at the same time.