Not sure... "at least 3", but it's entirely possible there is at least one under the 3rd (60+?) that's not obvious because it's been blended in w/ the bowl work. I recall seeing a close-up of a SBM that Hughes worked which clearly showed another 70-ish angle under the 3rd angle, so my a$$umption is the bottom angle has been blended it.
Different shops have their own ideas w/ respect to # of angles, width of angles, how far up they blend into the valve job, etc. Some stuff makes sense to me; other things I read about... ------------------------- EDIT: Including the Hughes work shown above, four different shops, four different valve seat configs... and possibly the only thing they have in common is a 45* seat.
