I have hit a wall in my assembly. The concern being that I’m seeing geometry between the head and pistons that I don’t believe is intended. In short, I think the conical part of the piston dome be parallel to the angle of the head. I think the discussion on the 356 Registry Forum confirms this is not just sub-optimal but problematic.
We have a B Super 90 head (22-degree) that was fly cut. The pistons are part of a new AA big bore kit that indicates 22-degree and “no machine work, when installing in factory Porsche (A/B) case & heads”
I have trial fit the head twice. The second time dropping the thickness of copper cylinder gasket to .75mm. I checked clearance with clay and deck height both times. As you can see in the photo, the piece of clay on the left (top) is narrowest in the middle of the conical part of the dome. For the right (bottom), it’s pretty close to aligned to the edge of the piston top. Results are consistent on all pistons.
The angles in the drawing are exaggerated intentionally, to make the contours of the head more obvious to me. The range of measurements across the 4 pistons are real.
A secondary challenge is getting desired deck height. I can’t reduce the thickness of cylinder base gaskets to get closer to desired deck height (1 mm) without increasing my compression ratio beyond what I understand is acceptable for a street car (9.5:1).
