[Roush #1]

If you are judging your engine octane requirements by "pinging" and are lowering the octane until you hear a ping, I would suggest you start researching engine builders as you are going to need one soon.
You can damage your engine extensively by saving a few octane bucks which is what it sounds like you are trying to do.
I would also suggest you start a new topic explaining what you have done to lower the exhaust sound enough to hear a ping. ;-)