I am an OS man if you have not noticed. I do not have my TZ in yet as I started running on a track about 50 miles away and it is VERY technical. The OS .15 CV-RX I have in it now is just about too much for the track and I know the TZ will be. The TZ has the most HP of any small block made to date out of the box. Being OS always is very conservative on the HP rating even thaw claimed HP is only 1.8 when put on a dyno it was putting out all most 2.3HP.