if you have the VAFC they yes you can tune for fuel and change vtec but you cannot adjust ignition and that is the problem. you may get some minor gains with it, but the fact that it cannot adjust ignition is why most of us DONT like it, if you dont already know honda has 2 a/f and igntion maps, an off vtec and an on vtec, if you change your vtec you should change your ign and a/f accordingly not just a/f.