[Jeepracer427]

ive been reading up on many sbc heads and i was wondering why the most radical valve angle is 9 degrees. why at is holding them back from a 0 degree valve angle?

[ap72]

Because a 0 degree angle would do more harm than good. There's more to a head than valve angle and if you consider what else move when you move the valve angle it becomes apparant why. Look at the head from the intake manifold to the valve face.

[Jeepracer427]

i understand that. my question is, does it have to do with the piston and valve posibly coming into contact?

[Silverback]

the overly simplified answer is that the more you make air change direction the bigger the restriction to airflow, and since intake side flow is usually generated by a relatively weak vacuum you for the most part want to minimize direction change as much as you want to maximize exposed valve opening area in the chamber.

For the most part, a flatter valve angle should result in less of a chance of the valve hitting the piston, but may cause more clearance and shrouding problems with they cylinder wall.