as they said, zero need for 9 (use 10) and don't waste your money on IR plugs for this machine. Pick up CR10EK . I have a motor with way more than just a full system, and all i use are cr10ek. Same with nearly all the racers and tuners i know. The flat electrode plugs are "claimed" to make another hp (as in maybe 1..) at high rpm. I have never seen a dyno sheet that clearly proves this.