You had two things going in your favor. One you used a blower instead of a turbo, which has a much cooler air charge than most turbos do and you were using alcohol, which again greatly cools the intake charge even more. Heat is the enemy on forced induction setups using turbos making them more susceptible to detonation compared to a blower which only uses the outside air to force into the engine instead of heated exhaust air.
Granted, it you add an intercooler and a methanol spray mist cooler, then you can help this to some degree with a turbo, but if you use gas instead of alcohol as a fuel, you will always be at the mercy of the detonation gremlins, and a boost retard will just be a part of life. And even with alcohol as a fuel in some engines, it still may not completely eliminate this issue.
