I believe there are a lot more factors taken into account these days for high-end performance valve seats. Valve angle, chamber style, lift requirements, RPM... all these -- and more -- seem to have an influence on the configuration.
Here's something I copied from a Darin Morgan post on SpeedTalk that could be a decade old easily. He's talking competition heads, but it gives a good feel for how much different the config may be than the traditional 30/45/60 3-angle. I put the valve seat angles in bold.
"Yes you can run a 50 degree seat on 14 and 15 degree heads and I have even seen it work on 18 degree heads just so long as someone has not blown the chamber out a ridiculous amount. I use a 40 degree top cut .100 wide, 50 degree seat .045 wide, 62 under cut .080-.090 wide and a 72.5 degree if I plan on blending and a 75 if I want to run sharp angles about .200 wide. I then set my throat diameter proportional to the valve diameter ( 90-91%). I think the real trick or should I say " rule" with steep angle seats is that if you do not have the material in the chamber for a top cut that is 10 degrees less than the seat angle itself and you can not continue that angle for at least .250, don't go there!
A 50 degree seat takes a 40 or 45 degree top cut at least .100 wide. If you have to clean up the chamber with a 35 or a 30 top cut, it wont work, period! You really need to try and not turn the air into the chamber any more than 10 degrees.
A typical low profile chamber on say a 10 degree valve angle ( like Pro Stock) has valve angles like this. 50 degree top cut for at least .300 then rolls back to about a 40 degree at deck surface. The seat is 55 degrees at .045 wide. the under cut is 65 degrees .090 wide and the last cut is a 74.5 .400 wide then an 85 degree .200 wide. This way by the time I am through blending the throat in, it turns into a 75 degree under the 65 degree. I hope that is not confusing.
These are common valve jobs I use. Notice the top angle differs from the seat by only 10 degrees or less, not 15 or 20.
35-45-60-70 Blend 70 up to 60 Good for concave chambers like conventional BBC heads. 18 to 26 degree heads, Dart, Brodix ect ect.
40-45-62-72.5 Blend 72.5 up to 62. Works good for chambers that are concave like 15 degree heads.
40-50-62-72.5 Blend 72.5 up to 62. works well for 12 to 14 degree heads with true convex or strait wall chambers.
45-50-65-72.5-85 Blend 72.5 up to 65. works well for 12 to 14 degree heads with true convex chambers. mainly for high lift, high valve speed, high rev engines that need good seat life.
50-55-65-74.5-85 Blend 74.5 up to 65. for heavily convex shaped chambers. 10-12 degree heads. For ultra high lift, super high valve speed, extreme high rev engines.
55-58-65-75-85 Blend 75 up to 65. Don't even go here! Its hard on seats and very tricky to make work. I hate it but its worth a little power.
58-60-70-75-80-85 Don't blend anything. leave everything sharp even the transition into the bowl. Not worth the valve replacement bill. Worth 4 horsepower above 8800rpm.
I hope this helps."
He also had some comments about his approach to reworking the late-model GM LS7 head, which is a production 12* valve angle raised-port LS-series head, not a dedicated race head:
"The chamber in the LS7 head was designed for low lift flow. The chamber is at 30 degrees off the 45 seat so any steeper seat angle will be a disaster. Some have used 50 degree seats in this head but they had to use very wide back angles cuts on the valve to turn the air and that just adds valve weight. I dont agree with that approach.
I like a 38 or 40 as well and i agree it would be better,,,,,,but,,, the chamber is already 30 and I hate to sink valves so I use a 30. Its the best compromise in my opinion.
