<VV> Valve Seat Fit

[Smitty Smith]

Smitty Says:  since I am the only one with an opinion worth listening to, here is mine.  .006 or .007 under seat size is a good place to start but here is something that is largely ignored.  The surrounding aluminum only has so much "memory".  That is its ability to return to a cool state compression around the seat.  The more force encountered by it trying to shrink against the seat, the less it is capable of maintaining that force on the next heat cycle.  So if you have a seat fitted at .005 and another fitted at .010, within very few heat cycles they will both be exerting the same shrink force on the seat.  I don't know of anyone who has pulled a perfectly good fitting seat out to measure the seat bore after a hundred cycles just to measure it so this will just have to remain my opinion.