"Psychological projection - Wikipedia
Psychological projection is a defence mechanism in which the human ego defends itself against unconscious impulses or qualities (both positive and negative) by denying their existence in themselves while attributing them to others."

Sodium is salt, correct?
I redid a Ford FE 427 Holman and Moody side oiler boat motor for a friend, I could hear something sliding around in the exhaust valve stems when I shook them

Only in part. Salt is sodium chloride (nacl).

https://www.google.com/search?q=sodium&a...me&ie=UTF-8

The 4.5 Mercedes V8 that was used for so many years had sodium filled exhaust valves. Lose the 6' long timing chain and one would find out. Back in about 1984 they were $28 each.

The deal is, the sodium doesn't fill the whole tube, only half. Then when the valve gets hot the sodium melts and physically transports the heat to the valve stem and head.

R.

Its actually a low melting temp metal, that is very reactive, one reason it transfers heat well in this application.

The A148 NASCAR hemi had them and I think John Aruzza told me that the Ball stud hemi had them as well. I have one on the shelf in my office.
Todd

If the 5.7 V8 still has solid exhaust valves,
and the 6.4 has sodium filled exhaust valves,
how could two owners design an experiment to measure
the effect of the different valves
on when a cylinder first has audible pinging in real world use?

Maybe some kind of hill climb on a hot dry summer day?

Sample quote

Compression ratio is another factor that affects performance and engine power. The only thing that creates engine power is the size of the explosion of fuel and air in the combustion chambers and more compression creates a bigger the explosion. Once compression ratios start to get bigger, regular fuel can start to ignite before the spark plugs ignites and this can cause problems. So to prevent that from happening, manufacturers recommend or require higher octane fuel (can withstand a greater compression before igniting) on engines that have higher compression ratios.

The 6.4L SRT engine has a compression ratio of 10.9:1, which is significantly higher than the 3.6L engine’s compression ratio of 10.2:1 or the 5.7L HEMI engines compression ratio of 10.5:1. Premium gas (highest octane) is recommended for the 6.4L SRT engine, whereas midgrade gas is recommended for the 5.7L HEMI and regular gas is recommended for the 3.6L engine.
End quote

Truck version of the 6.4 has a lower static CR of 10

From
https://www.universitydodge.com/dodge-gearhead-6-4l-srt-engine-performance-specs/