Most FE Intake Valves are cut at 30 degrees. This lends itself better to midlift flow, and flow at around a .500" lift max(like most 390HP, 406, 427 and 428 performance factory Cams).
A 45 seat will net you more flow at higher lifts(over .550" - .600" +), at the expense of midlift somewhat.
My 385 Heads have 55 degree seats. Very good flow at hi lift, but a lot of maintainence, also. Most of my FE stuff is run between 45 and 50. Hope that helps.
Dennis(RiverRacer)
Ford Racing Components
www.dscmotorsport.com
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