I have been running OS plugs in my S7 with no problems. The plugs that I use with that motor are OS R5 and 8's. I've raced many races with the OS plugs in my RB's. The rule of thumb that I have boon using is that a short plug will work in a long plug button. The result is lower compression and a little higher RPM. I have not found any dammage or lack of power running a OS plug in my RB.