Horsepower TV did an episode a couple of weeks ago showing a 10 hp increase (going from memory) by going to an E3 spark plug. I believe summit sells them for like 4 bucks each. They said they compaired them to a similiar performance brand spark plug. It would be interesting to hear from any one who has experiance with these plugs. But with any claim in hp gain, it all depends on how the motor is set up.