Too much octane will have a negative effect on an engine not needing higher octane.
No; using fuel with more octane than the engine needs will have a negative effect on your wallet.
Well, I had a 400 with 5C heads and was running a blend which came to roughly 100 octane. I was at 8.8 to 1 compression. I did not know what heads were on car because they were ground off. When I switched to 87 octane, the car ran exceptionally better with no other modifications after I pulled heads and CC'd chambers. That was circa 1990 or so.
Anomoly?
Likely, but hard to say without testing both fuels. What were you using for ignition?
