Valve Shape and Angles

[Kapt. Krunch]

What are the different characteristics associated with valve shapes? I don't mean ovals vs triangles (joke)...I mean the angles on the back of the valve.
I typically had the standard 45degree seating angle and then a 30degree backcut behind that. good results but I'm very interested in knowing if a "diffuser" angle after the seating surface is of any benefit over the standard perpendicular or straight side.
Any insights?

 

[Rich Rohrich]

The threads linked below touch on the basics :

http://www.dirtrider.net/forums3/showthread.php?t=124408&highlight=diffuser

http://www.dirtrider.net/forums3/showthread.php?t=125800&highlight=convergent

 

[Kapt. Krunch]

Thanks for the pointers Rich. I will grind accordingly. :)