Anyone know what it is?

Thanks.

 

Using a plane 90* from the head gasket surface, as a reference, the intake MANIFOLD surface is angled 10*, from that plane. Or stated another way, 80* from head gasket surface. So the answer, you are looking for, is 10*.

(I believe) an engineer, back in the 50s, or earler, decided it could be more confusing THAT way, to determine the angle to declare, in lieu of, simply using the head gasket surface, as the reference. We would then simply state that it (head) had a 80* intake face.

 

Thanks Arnie!