Originally Posted by sook

Thanks AFM.
All I know is that when I used the os plug in the sts engines, it leaked. I would have to imagine that the conical tip did not match or seat well in the head of the sts engines. It leaked just as rushdude described. I even tighted it down and eventually it leaked again causing tuning issues and higher temps. I even tried the Rossi Ultra plug, which was a short body plug and it continued to do the same thing as the os plug. Once I switched over to the Novarossi long bodied plug, it sealed nicely and no more issues. Unexplainable, except that the seat of the conical shape fit better than other plugs and had a complete seal.