It's this simple.
If you have an engine with racing cams, you can make 100 hp per liter easy. No sweat. Just give it cams big enough to breathe at engine speeds in excess of 7000-8000 rpm.
The one problem is, it won't idle. It'll run like garbage at low rpms. Because those big cam lobes and large overlap mean that too much air is going in, and the volume causes all kinds of turbulence and low-velocity problems in the intake and exhaust ports.
If you've got a big-cammed car, you'll need to idle it at 2000 rpm to keep it chugging.
VTEC allows you to have two cams. The big cam and the small cam. The importance of VTEC is that your unstreetable racing engine can now idle at 700 rpm like every other engine and won't stall when you're pulling out of the parking lot. But put it on the racetrack against a non-VTEC engine with the same high rpm cam, and performance will be the same, except from a slow roll, since between shifts, you should never fall below the rpm at which the large cam activates, anyway. Not unless your gear ratios are all messed up, like my Mazda's... but that's another story.
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VTEC is so effective that almost everything has variable valve timing and lift nowadays, from the dinky Corolla to the Mustang V8.
Does it make power by itself? No. Does it enable a car to offer more power than the manufacturer would have otherwise given it? Definitely Yes.
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Bigger cam lift will make more power wherever the stock cam lift is insufficient. It depends on the specific tune of the motor. Too much lift, though, is bad at low to medium rpm.
Bigger cam overlap will only make more power at high rpm. This is why variable valve timing and phasing are important.
and didn't know much but now I do.
