| The volume cc'ed from the cylinder head only, with spark plug installed. |
| Measured gasket thickness with a caliper. Tip: you can decrease this value accordingly to see the effect of decking the cylinder or milling the head (as long as no material is removed from the inner part of the chamber). |
| Gasket inside diameter is slightly larger than the bore. |
| Use a caliper to measure the actual bore diameter or use the published bore specification (if not bored oversize). |
| Measure down from the edge of the bore or a fixed surface, such as a piece of bar stock laid across the bore to a point on the piston above the wrist pin and along the edge of the bore. (This minimizes errors due to the piston rocking.) |
| Measure the distance from TDC down to the point at which the top piston ring finally seals the exhaust port. |
| Some pistons stick out past the cylinder deck surface, therefore pick a point about 1/8" under TDC to CC the cylinder. Record the height down from TDC. |
| This is the volume above the piston and top ring, in the cylinder, up to the deck surface. |
| If the cylinder is CC'ed at a point below TDC, then the volume between that point and TDC is subtracted to obtain the actual TDC deck volume. |
| This is the volume 'swept' from the point at which the exhaust port is closed (sealed cylinder), and TDC. |
| The effective or trapped compression ratio is defined as the ratio between the volume that exists when the cylinder is considered sealed (exh port closed), and the clearance volume at TDC. |
| The geometric compression ratio is defined as the ratio between the volume at the bottom of the engine's stroke (BDC), and the clearance volume at TDC. |
| If the cylinder was perfectly sealed (no leaks past the rings), and there was no flow restriction to the cylinder, then this would be the approximate pressure reading on a compression gauge. |
| This parameter is only required for calculation of geometric compression ratio, or 4-stroke engines. |