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I have a set of 1976 3.0 turbo heads for a 95mm bore sitting in a box waiting to have the edge of the combustion chamber beveled one full mm into the squish band all the way round so I can use them on a 3.3 with 97mm bore.
I'm mentioning that because I've measured with calipers and the intake ports are 32mm just like a later 3.3 head.
It's the exhaust ports that are 2mm wider in diameter and that seems to be in the middle part of the exhaust port area a little after the valve guide and before the before the exhaust port flange. The port diameter right at the flange is the same as a 3.3 so the exhaust headers match up the same.
The port sizes for different years of all the air cooled 911's are in the specs in the back of Waynes book.
I've heard the reason for the half finned 930 cylinders was to try and keep the clamping force of the 4 headstuds closer to equal. The exhaust valve side of the head runs alot hotter than the intake side and do to heat transfer the cylinder and the headstuds do too. This causes the headstuds on the bottom or exhaust side to expand more and the clamping force weakens on the bottom side leading to the bottom side of the cylinder heads lifting under high boost.
So, Porsche removed the cooling fins on the top side or intake side of the cylinders to try and equalize the heat in the cylinder and maintain closer to equal expansion rates of the cylinders and headstuds for better sealing and less chance of warping or leaking.
and, I don't know for sure if that is correct or not.
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