I came across an article in Hemmings today that got my interest and I thought it was good to share here. https://www.hemmings.com/stories/how-to-compute-compression-ratios/?utm_medium=email&utm_source=EDaily&utm_campaign=2024-05-20&uemlid=d718ac2cb9e3d4324252aaa77e5b37cc2e8120402e6bc8153ba3cee92430360c  One of the examples they used was for a 283.  It said:

"The stock bore and stroke on a 283 is a combination of a 3.875-inch bore and a 3.00-inch stroke. With a 58cc combustion chamber, a flat top piston with four small (for a total of 8cc) valve reliefs, a 0.020-inch below deck height and a steel shim head gasket that is only 0.015-inch thick, the compression ratio for this engine comes out to 8.96:1. But often hot rodders will bolt a 64cc head on a 283 with bigger valves to try to make more power. What they dont realize is that with a very short 3.00-inch stroke crank, a small chamber increase in size of 6cc has a big effect on compression. This change to a 64cc head will skewer the original compression ratio of 8.96:1 to 8.35:1 or a loss of over half a ratio!"

My 283 was bored 40 over and I installed 520 heads.  I looked it up and they have a combustion chamber of 59cc compared to the stock 58cc.  I used the gasket numbers in their example and went to Summit Racing to access their calculator https://www.summitracing.com/newsandevents/calcsandtools/compression-calculator

My results are:  Compression Ratio 8.99: 1 with total displacement 288.17 cu in.

The Summit site talked about ratio and fuel type, mentioning many muscle cars of the 60's, had ratios of 11 : 1.  After reading the following about today's fuel I felt pretty good about my ratio:

"With todays fuel, most sources will suggest no more than 9.0:1 for a compression ratio with iron heads. Our experience indicates you can run closer to 10:1 if the piston-to-head clearance is tight and the heads offer a decent, more modern chamber like the newer LS engines, for example. Older engines with poor chambers tend to rattle with more than 10:1 to 10.5:1. Camshaft timing also has an effect on performance with bigger cams demanding more static compression compared to a street engine with milder cam timing. These engines are run more favorably with less compression. Of course, the more compression, the more power the engine will make with better efficiency so its a critical point."