shorter than the stock NGK's. I use them and so does my friend who got me into the Z. He has them on his supra and made 400+ rwhp with iridiums. Many here have claimed poor idle and a host of other problems they attribute to the iridiums. I have no probs with them and use them on all my cars and my 2 turbocharged bikes running 20lbs of boost. You can try them and if you don't like them take them out and get stock. You will not hurt anything. You can run 12lbs with any good plug, it would be better to have a plug that is at least on stage colder.