I have a msd rpm activated switch (can change between rpm "pills" to cut on vtec or whatever accesory u would want to hook it to) that i will let go cheap if you are interested, it was used on my old H22 accord for the vtec, but like what you are saying about using the tach, you would need to adjust/raise the fuel flow from the rpm when vtec engages all the way to redline to get the full potential of the motor, i used this and a safc before i found a p13 ecu for the Acclude and ran a couple tenths of a second quicker in the 1/4 with this setup...although prolly not as safe as the vtec ecu