you can run 30% out of the box but if you find your plugs dont last put the extra shim in. Some will run on some will pop plugs at factory shimming. It all boils down to many things that i dont have time to go into.

Realise that more shims makes a steady idle , less shims makes the idle a lottle narrow to tune but better economy . More shims = less torque but freeer top end charge , less shims = more snappy torque , slightly less top end.

If you want an average down the middle set up run 25% nitro .5 shims total , Medium plug . 7.5 restrictor.

MASSSIV E!