Spark plug protrusion vs chamber volume

[65dragster]

This might be a dumb question, but here goes. Once a cylinder head combustion chamber volume is determined by pouring the chamber, will the spark plug type/heat range or protrusion into the chamber affect compression ratio? How would this be measured or calculated if it is a factor?

[Caprimaniac]

Did you cc with byrette and fluid? If so, if you used an old plug in the hole (which is identical to you new plugs), that volume will already been taken into account.
0,25.0,5cc? Depending on

[65dragster]

Thanks for the reply. I was curious if it would make a meaningful difference if I change plug style or heat range.

[BlitzA64]

Meaningful in compression ratio not really. Meaningful in a limited class where there is a cc minimum on head chambers likely if you are right on the number.

[David Redszus]

The effect on compression ratio due to spark plug intrusion is a function of combustion chamber volume.
It has some small effect when inserted into a very small chamber; a large chamber, not so much.

[65dragster]

Thank you for the insight. I won’t worry about such a small difference since it isn’t in a strict NHRA class.