What does it do for your motor to have the valves oversized? What part of the valve is oversized, the stem or the head. If it is the head of the valve then I can understand this letting more feul in (as long as you shave the head to fit the valve). Is this what it does or is is something else?

 

I believe it's the head that's oversized, and you shave the valve seat to make it fit.. i think SS valves go for about $20 each (ouch)