Old Britts – Calculating Compression Ratio and CCing a Cylinder Head
Download the complete PDF version using the green download button at the top right of this page for a detailed Old Britts technical article explaining how to calculate engine compression ratio and accurately cc a Norton cylinder head. Written by Fred Eaton, this workshop guide walks through the formulas, measurements and tools required to determine true combustion chamber volume and compression ratio on Norton twin engines.
The article begins by explaining the compression ratio formula and how to calculate swept cylinder volume using bore and stroke measurements. It then demonstrates the complete cc’ing procedure using a burette, Plexiglas plate and ATF fluid to measure the combustion chamber volume accurately.
Further sections explain how to account for piston deck height, head gasket thickness and piston crown intrusion into the combustion chamber when calculating total clearance volume. The guide concludes with a worked example using a Steve Maney short-stroke 750cc Norton engine fitted with 850 pistons, resulting in a calculated compression ratio of 8.88:1.
Contents Include
- Compression ratio calculation formulas
- Swept cylinder volume calculations
- How to cc a Norton cylinder head
- Using a burette and ATF measuring fluid
- Plexiglas plate setup and sealing methods
- Removing air bubbles during measurement
- Measuring combustion chamber volume
- Calculating piston crown intrusion volume
- Head gasket thickness calculations
- Worked example using a Norton short-stroke engine
- Depth gauge measurement procedures
- Compression ratio calculation examples
