OT: VVTi and VTEC engines etc...

Having run a Honda Accord 2.2 Type-R as a company car I have a reasonable idea:

You have 2 sets of cams and timing - nail the throttle and it accelerates strongly in a linear fasion until 5750 is reached, engine then swaps to juicy cam and timing mechanically and takes off like a cat with a firework up it's jaxy until around 8000rpm when you grab the next cog!

NB whilst 30mpg was possible from above car, it used a pair of 215x45x17 Bridgestone RE010's at £180 each every 4500 miles. . . . . .thank god for full maintenance contracts, as I was costing nearly as much in tyres as the monthly payment was! :D

Yep. The reasoning is that at higher RPM the fluid dynamics of the fuel/air are different to those at low revs. There is no 'perfect' cam for all engine speeds, so the use of two allows smooth, economic running at low speeds and max power at high speeds (and higher maximum engine speeds). A 'max power' cam would run like a pig at tickover, which I guess is why race cars are so easy to stall.

BMW sixes have long had a similar system, but continuously variable. Double VANOS or summsuch.