Piston compression height measurement

[64SF]

In reading the description for a set of piston they are described as .030 over with a compression height of 1.912 inches. What does the compression height measurement mean and how would that calculate (if it does) in the compression ratio of the engine. They would be for a 440. I tried a search on this thread but didn't find an answer. Thanks

 

[lewtot184]

the compression height is the distance from the center line of the wrist pin to the top of the piston (domes are not used in the measurement). with a given stroke, deck height, and head cc the lower the height the lower the compression. 70-71 six-pak pistons were 2.06, 68-70 4bbl and 69 six-pak were 2.03, and if i remember correctly 67 440 was 2.0 (1.99?).

 

[Meep-Meep]

If the pistons you have are completely flat you can do a rough calculation by using the formula to figure volume of a cylinder.

Bore squared x .7854 x distance.

You can theoretically figure the distance in the above equation by taking the stock 440 rod length of 6.76" + stroke of 3.75" and subtract that from the theoretical deck height of 10.7". The difference is how far the piston is in the hole. From there you add that to the chamber volume, including the gasket volume to get the total chamber volume. Then the final answer is volume at TDC divided by the sum of swept volume plus chamber volume. Make sure to keep the units the same. Chambers are usually in CC's so convert the swept volume to cc's as well.