"Interference angle" seating, 45 degree valves and 46 degree seats, is a quick production method to turn out a lot of heads in a hurry at the factory. On any precision buildup I do, whether for racing or trailer towing, etc. I always do a 3-angle valve job. It's possible to custom-tailor valve seat width to the type of engine operation, narrow for speed and horsepower, wider for heavy load applications. It's worked for me for over 40 years, with no concerns about short valve job life except for maxed-out race engines that aren't expected to last long anyhow!
Jerry
