What is the difference between the different octane APR chips? (ex. 91octane - 93octane)

i would like to know about this too

The key differences between the programs are that more aggressive tunes can be safely achieved with higher octane gas. You'll have a higher horsepower tune with each higher octane program. They aren't different chips. They're different program options on a reflashed ECU. Read the other thread just below where someone was talking about their APR tune they just got done - I elaborated more on there.
http://www.audiforums.com/m_586063/tm.htm

Tristan
Velocity Factor