All of the above mentioned do not work very good because of the ignition style (coil packs) in our cars. The coils packs produce a positive and negative discharge causing 3 of the plugs to fire from the center electrode out to the ground, and the other 3 fire from the ground to the center. The rapid fire and split fire plugs were designed around a conventional firing ignition system (firing from center out). I have never used any of those in my T Type, but I did run split fires in my 84 regal in which I had a 455 Stage one. With the split fires I could get away with 3 to 4 degrees more ignition timing (w/o knock on 93 octane) and I could tell the difference coming out of the hole. I would definitely recommend them to someone driving an older V-8 performance car. Sometimes I miss driving the big block car.