I have been using actual seat O.D. for over 30 years to measure the true percentage difference and, as I said ... anyone can use whatever dimension they want to use.Rick360 wrote: ↑Mon Jul 16, 2018 7:07 pm % of valve diameter is what most are referring. For a given valve size you can do the seats a hundred different ways that could give you different throat % if using a valve seat reference. Typical conventional seats has the seat OD the same as valve OD so it wouldn't matter. Throat % of valve od makes sense to use since that indicates how much room you have to make your valve seat and bottom cuts in any manner you want.
I had not heard/seen anyone mention throat to valve seat % before reading it in this thread.
Rick
EVERY single head from any O.E.M. manufacturer, (MILLIONS of heads), has the seating area considerably inboard of the valve head diameter. Now they certainly aren't race heads but, I definitely would consider them CONVENTIONAL, especially when trying to make comparisons.
Again, use whatever dimension YOU want.