[Healeys] pinging & knocking

[warthodson at aol.com]

I am helping a friend to reduce/eliminate the pinging/knocking his BJ8 is
making.
This is an interesting discussion on the subject:
http://en.wikipedia.org/wiki/Engine_knocking

Here are some basic facts about the car. The engine was professionally rebuilt
about 8-10 years ago. 9.5/1 compression, hardened valve seats, the cam is
slightly more aggressive than a BJ8 grind, 3 HS6 SU carbs, Advance Distributor
rebuilt the distributor recently (the pinging pre-dates the distributor
rebuild), Pertronix ignition, the valve lash is correct, the carbs are not
running lean. Fuel is "premium" pump gas, what ever that is.

Timing:
without vacuum advance connected: 1000 RPM = 10.5 degrees/ 3000 RPM = 25
degrees
With vacuum advance connected : 1000 RPM = 13 degrees/ 3000 RPM = 35 degrees
At the above settings we are experiencing slight pinging with the vac. advance
connected.

I have three very basic questions:
1. It is my understanding that the timing should be set at max. advance
without the vacuum advance connected. Is this correct?
2. Max. advance should be in the range of 30 to 35 degrees, without the vac.
advance connected. Is this correct?
3. Since pinging/knocking is not caused by the spark, why does retarding the
spark reduce the pinging/knocking?

Feel free to provide any other related or unrelated information!
Thanks,
Gary Hodson