Edelbrock 2.055 (30 degree back-cut) testing
D
Have you ever done any testing with a 30 degree seat & valve face? I know it's not the best HP setup but I read an article where Dulcich suggests it... He says it improves flow from .100-.400 without hurting flow at higher lift much.... He went on to point out the valve sees that .100-.400 range twice for every one time it sees max lift so gains down low can have a bigger effect than max lift flow... He only suggests doing it on the intake side.... I thought it was an interesting idea... Especially for guys like me who only run 550ish lift cams....
David Vizard discusses valve angles in his videos and his How to Port and Flow Test book. He mentions that Cup Car teams are using 50° to 55° seats. I do not remember if that is for intake, exhaust or both. He also mentions 30° intake seats do flow better especially at low lift, but 30° seats tend to bounce more.
For the Uncle Tony Mission Impossible 318 they are looking at 40° exhaust seats for improved low lift exhaust flow.
In one of his videos, David shows unshrouding valves using "flow balls" used as clearance guides. Port flow is area ruled at low lift. What this means is the flow through the port at low lift is not restricted by the port cross sectional area, but the area between the valve face and the seat. He starts by scribing the cylinder bore or gasket bore on the head deck, as this is do not exceed area for unshrouding. Now depending on the casting thickness, you can undercut the combustion chamber wall by the valve. David starts with a 1/4" ball welded or brazed to a length of welding rod. Lift the valve just enough the ball will pass through the seat area. Then check between the valve margin and casting wall. Where it will not pass, a little grinding is required. Do all cylinders with that, and then go to a 5/16" ball and do the same, working up to 1/2" clearance. Keep wall thickness in mind and do not grind through looking for that 1/2" clearance. DV goes through this on a SBF head but the principals are relevant.
Once you get to .27D of the valve head, the port area becomes the flow control factor. As DV relates, pick the low fruit first and work your way up. So this is the valve seats and the entry and exit 1/2" from the seat. Then generally the area by the valve stem and guide are next. Let the flow go the way it wants to go and you want to enhance flow on the cylinder wall side of the port by grinding on that side and grinding the port roof on the cylinder wall side. This enhances swirl which enhances combustion efficiency.
For the exhaust the quench area needs to be shaped to enhance exhaust flow directly out the exhaust port.