Overview
Otherwise known as "cc-ing" (cubic centimeter), figuring out the actual combustion chamber volume is important in calculating the compression ratio of your engine. Even though you can use the factory or manufacturer's figures, we think it's always a good idea to take the measurement yourself. This is especially important on a set of used heads which may have been previously milled.

You can build your own measuring kit inexpensivelyusing a piece of clear Plexiglas and a syringe (preferably 60cc or greater.) You'll also need some Vaseline® and a colored liquid, such as glass cleaner. The instructions below show you how easy it is to figure out the volume of the combustion chamber.

The process is simple. Take a piece of Plexiglas and drill two holes, one a 1/4" and the other an 1/8". Install the valves for one chamber and seal them with a light bead of Vaseline. Also screw in the spark plug. Then place a thin layer of Vaseline around the combustion chamber and place the Plexiglas down flat to seal off the chamber.

Fill the graduated syringe with glass cleaner or water and a drop of food coloring. Note the volume in the syringe. Slowly dispense fluid into the chamber through the 1/4 hole (the smaller holes serves as a vent.) Periodically tap the glass to remove any air bubbles. When the chamber is full, note the remaining volume in the syringe. Subtract the remaining volume from the starting volume to obtain the volume of the chamber.

Conclusion
It is a good idea to repeat the method several times to insure you get repeatable results. You should also check at least one chamber on each cylinder head to identify possible inconsistencies between the two heads. We have found new heads with as much as three cubic centimeters difference between the pair.

To reduce the volume, which results in an increase in compression ratio, you can have the heads milled. In order to increase compression ratiot there is not too much which can be done. In some cases the chamber can be ported to increase the volume. Thicker head gaskets are also a potential option.