<VV> No Spark Knock ?

[Allen Miles]

I own a nice 64 Vair 4 speed with a 95HP Engine .  The GM shop manual says to  set Timing 2 degrees BTDC .  Corvair Basics says 6 Degrees . I am running 11 to 12 degrees with no spark knock , unless I am lugging at low speed in 4th Gear . I have a Ignitor I I from Clark's (no points) I run premium fuel 1/2 of the time middle grade other times about a 50 / 50 Mix . Why am I hearing so much about Spark knock (detonation) and I am running about 5 degrees above Std settings . My Vacuum advance is OK and Centrifugal Advance is working  in my Distributor .   My Vair is running perfect .  Just asking for Info .  Allen