When building a VW engine, you must adjust the engine's deck height (space between the top of the piston and the top of the cylinder) to increase or reduce the combustion volume . This setting allows you to assign a specific compression ratio based on your needs. To achieve a desired compression ratio you enter the Bore, Stroke and two of three variables: Deck height, Cylinder head CC, or Compression ratio. You would then select the button at the bottom chart to solve for the missing figure.

To measure your deck height, you will need a deck height measuring tool which looks like this. It calculates the distance between the top of the piston at top dead center(TDC) and top of the cylinder. You will also need to know the volume of the cylinder head combustion chamber in CCs. This is measured with a cylinder head CC measuring kit which looks like this. There's also a metric converter included.

For instance, if your building a 2110 engine (90.5mm Bore x 82mm Stroke) and you know your cylinder heads have a combustion chamber volume of 56cc. To determine the deck height required for a compression ratio of 8.5:1, plug in the following numbers: bore=90.5mm, stroke=82mm, combustion chamber volume=56cc and desired compression ratio=8.5. Click the 'deck height' button and you'll be given the answer: 0.088" (or 2.23mm).