Club 80-90 Forums

CNC contour milling will be involved at some point! A few pics to start off. L to R: later efi type "big valve", very late "reduced compression", AMC.
Note the difference in combustion chamber shape, valve shrouding and the obvious need to port some AMC heads if you are blueprinting or looking for performance.

AMC ports:

They can be a bit offset:

Looking at squish on the reduced compression head. Food for thought, the shaded area matches the DJ piston.

Quite why VW machined the while area back is a mystery, the barrel fire rings are bang on for optimum combustion thickness at ~1.15mm (the ideal range is 0.035 to 0.045")
The spark plug is also showing its last thread, so it loads up with carbon and spoils the thread on removal...