breeza, if your gonna use your method, i did it before long ago.

What you normally do is turn on the a/c to turn up the load before driving.
I used a timing gun and turned it up a degree at a time, then when it started to ping we dropped it back 1-2 degrees. Best done on a hot day with a/c on.

Its a cheap free increase but don't expect too much, may loose abit low end though