A vtec engine with stock cams and no tuning loses power just before vtec engages. It is a marketing scheme to sell cars. With out that lose, the rush is not as great at the switch over point. People think just because it hits hard and gets loud it must be better.
Also, a cooler engine will make more power. That is why you let a car cool down between runs on a dyno. The more heat soaked a car gets the harder it is to reproduce the same HP numbers.