This has alway interested me and I have both manuals, so I
compared engine specs as published by Haynes in their 914
and Vanagon manuals.

Vanagon 2.0l (this could be British spec, not sure)
compression - 7.4-1
intake valve - 39.3mm
exaust valve - 33.0mm
horsepower - not listed

VW-Porsche 914
compression 8.0-1
intake valve - 42mm
exhaust valve - 36.0mm
horsepower - 100

Is there information anywhere on using the bigger valve
heads and/or higher compression pistons while retaining the
fuel injection?