Ferret Ignition Timing?

[LRDG]

Another Ferret question: I found the ignition timing of the Ferret I am working on at 25 deg BTDC. It still idled reasonably well. I corrected it to the spec 0 deg BTDC and maybe it idled a bit better.

I can't help feeling 0 deg BTDC is too retarded with modern gas.

Retarded timing can cause hot running and it definitely reduces power and increases fuel consumption. Typical static timing seems to be 10-15 deg BTDC on other vehicles, albeit more modern ones.

Combustion rate with 60 year old combustion chamber design and a 6.4:1 CR must be a bit sluggish so I suspect the engine would benefit from some more ignition advance.

I don't expect us to try hand start the old girl so I don't see that as a significant issue.

So I am considering advancing the timing to 10 deg BTDC to see if it makes any noticeable difference. I think the 25 deg added by centrifugal advance to give a total of 35 deg should still be safe, what with modern gas having lots of detonation resistance compared to old-time gas.

Has any one tried this? Any comments?