I agree I think that advanced timing is as big a culprit as compression ratio.
Your comments about the combustion chamber design are interesting - did you also have run-on after the key was turned off? That could be glowing carbon build up.
Some also worry that gas from the old days was different/better or higher octane then today - from what I have read the difference is or more what fuel engineers call 'sensitivity' then an absolute difference in AKI number:
Bruce Hamiltion's Gasoline FAQ The pump number or AKI is R+M/2. Today's fuels have as much as a 10 point spread - so today's 87 actually has a higher R then yesterday's leaded stuff (92+82)/2=87 versus (89+85)/2=87. Since the old leaded gas actually had lower R and higher M - they were much less likely to knock under sustained high loads. And is why lead is still used in boats and planes. As I understand it today's gas is formulated with a higher R number to avoid run on - and not so much to prevent knock.
For me I assume that if one is building a hot rod one designs with high test in mind - but doesn't get so crazy that one needs to take Gerry cans out the airfield for AVgas!
regards,
stock49
