The octane level in your fuel is actually what helps to prevent the knocking. If you are getting knocking with the 87 octane, chances are moving up to 89 will correct it.

From http://auto.howstuffworks.com/question90.htm
The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

Mike

EDIT: Sorry, didn't mean to bring back an old topic. I was just researching which programmer to use and thought this may be helpful to some.