My engine was designed to run on 100 octane with 36 degrees total timing. It runs GREAT on true 100 octane from the pump (not bottled additives). Running on 93 octane (7% reduction) requires me to retard timing by 7%, to 33 degrees total timing, to avoid heavy detonation. I can accomplish this by setting initial timing to 6 degrees BTDC instead of 9 BTDC, so if I happen to come across good fuel I can quickly adjust for it. Unfortunately, as it is a compromise, I don't have all the power that the engine should be able to provide.
Kemcooil Lead Supreme 130, one quart per tank, gives a slight improvement. Not what the label claims, it does not allow me to put the timing back but does allow me to drive a little harder with the retarded timing with no detonation.
In an ideal world, I'd be able to easily change distributor limit bushings or adjust the slot and take the timing out there.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
