I have read where when vtec engauges it does take a second to be fully functional. your going from one cam profile to another and doing so you change the amount of air entering and exiting the cylinders. this won't happen in an instant.

As far as porting goes I put a Z6 ported on my stock Z6 block about a weekago. At first it was very lazy almost like the stock DPFI. I thought I made a big mistake. I was told advanced my timeing about 20 deg. and it was like driveing a new car. fuel milage had droped considerably and idle bounces few hundred rpm at idle but my need to adjust the AF screw.