A friend of mine has a 99 civic si with only intake and exaust. After getting an oil change, the vtec does not seem to be making anymore power. Vtec can be heard engaging but no power is put down at the wheels. The motor seems to just get loud, but you cant feel any power of the power that it usta have. I told him that maybe the oil was low, and that could probably be a problem, seeing as how vtec uses oil pressure. or something could be losse causing a drop in oil pressure, I.E. oil filter, causing vtec not to fully engage. I was jst pullin shiit outa my ass when assesing the problem but it made sense to me. Seeing as how i have no real experience with vtec, i was wondering if any of you smart people on this site could help me out i helpin my friend solve this problem. The symptoms of the car are listed above. Any info or facts about vtec are welcomed. Thanx in advance.