My 2001 Civic doesn't have a VTEC, but from personal experience, I can tell you that as long as you stay around 55-60, you should do great. Mine just got 37MPG on a trip I took last weekend, and the car has 75,000 miles on it since I bought it new. Road conditions as well as weather and terrain will play into it as well. Going thru the mountains on PA, the car dropped off to 27, but when I was on the Carolina coast, it jumped up over 35.