Dark- no I didn't shim the head at all. I'm using the R6 plug. I believe it's the Sirio R6, but pretty much the same as the P6. Just so happened I left the P6 at home so I used a new R6 that was in my box. It runs good, but I can tell by the idle characteristics that it could use a plug just a hair colder or hotter- not really sure without trying it.