You have it flipped...
Just one reference ... http://www.type2.com/library/engineg/ping.htm
"Pinging sounds like rocks being thrown around inside your engine. It will never happen at idle, may happen at part throttle, but is most likely to happen at full throttle. It is usually accompanied by a small amount of smoke out of the tailpipe, but don't rely on that.
Pinging is like... taking a cutting torch to your combustion chamber. Your engine can stand anywhere from less than one second to perhaps minute of pinging before it suffers permanent and serious damage, depending on conditions.
The hotter your engine is, the more likely your engine is to ping. The farther your timing is advanced, the more likely your engine is to ping. The higher your compression ratio is, the more likely your engine is to ping. The lower the octane of gas you use, the more likely your engine is to ping.
So, in order to minimize the risk of pinging, do the following:
1. Make sure your engine doesn't over heat!
2. Make sure your timing is not too far advanced.
3. Make sure your compression ratio is not too high (< 7.5 to 1)
4. If necessary, use higher octane gas.
If you take care of the first three, you shouldn't have to worry about the last one"
Note: Newer engines like the Hemi have protection against it, but lower octane gas is never good... Also note that not all octanes are created equal. Some may be more 'watered down' ;-)