Combustion Chamber Volume
To properly calculate the compression ratio of an engine, you need to know the combustion chamber volume. This can be called "CCing" the chamber. In other words, measuring the combustion chamber volume in cubic centimeters. Since I had large valves put in my cylinder head, I was pretty sure that the volume would have changed somewhat. Also, during the porting process, I did some unshrouding of the valves and polishing of the chambers. The polishing was done to reduce the size of any lumps or other irregularities. Think of these as a cooling fin with a temperature gradient down it. Just like the spark plug, the tip of the lump will be hotter than the base since it is further from the cooling source (cooling water.) This hotter spot can lead to pre-ignition (detonation) which can be destructive and will limit the amount of boost that can be run. In any case, I had done a little work polishing and grinding the chamber which changes the volume and compression ratio.
Of course the compression ratio is the ratio of the total volume, to the volume that it gets squished into. This "squished" volume would be made up of the combustion chamber volume, the volume that would fill the bore in the cylinder head gasket, and the volume that would fill the block to the level of the head gasket at TDC (mainly comprised of the dish in the piston.) TDC is top dead center, meaning that the piston is at its highest point of travel, resulting in the lowest "squished volume." The total volume would be the squished volume + the "swept volume." The swept volume would be the cylindrical shape that is traced as the piston moves from BDC to TDC. It is just bore times stroke. When I rebuilt my engine, I had the block bored 0.020" over to have larger pistons fitted. This would raise the compression ratio, since it increases the swept volume, while leaving the squished volume pretty much unaffected. I will be measuring the volume of the block too, so this aspect will be covered as well.

The CC kit that I borrowed from a friend at work is very simple. It allows you to seal off, then fill the combustion chamber on the assembled head and determine the volume of water that was required to fill it. The kit contains an acrylic plate with a single counterbored hole in it, a graduated cylinder (marked in CCs), and a short instruction sheet. The fluid that I used was a mixture of water, blue food coloring, and alcohol. The food coloring makes it visible and the alcohol cuts suface tension of the water (your enemy here.)

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You seal off the individual chamber using a very thin layer of vaseline. Then you fill the graduated cylinder and note its volume. I just filled it to the 100cc mark. You slowly add the fluid and fill the chamber. When its full, you note the level left in the graduated cylinder, and the difference is the volume of the chamber. All four of mine worked out to 60cc +/- .5cc.

A couple of hints. Tilt the cylinder head slightly by shimming one edge. Also, locate the fill hole at the top edge of the combustion chamber. This allows the bubbles to move toward the hole, and you can completely fill the chamber. That's all there is to it.

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