The simple answer:

The VVT-i system on your buddy's tC varies the timing of the intake cam, while i-VTEC varies both the cam timing and the cam profile itself. Depending on which i-VTEC engine you're talking about this could be either on just the intake or both the intake and exhaust.

The more complex answer: https://www.honda-acura.net/forums/s...ad.php?t=34779