I was researching the knock sensor of our cars and came across an article about a Nismo tuned 350Z. I copied a part that I found interesting for us octane challenged states.

"Even in stock form, the 350Z lives its 91-octane life on the knock sensor, and with the ECU retarding timing almost as fast as the NISMO parts increase cylinder filling, there's no power to be had. What NISMO needs for the octane limited is an ECU with a less aggressive timing map, but it doesn't have one at this point.OK, enough crying about our gas. If you live in the land of 91, be prepared to splash in a few gallons of $6.00/gallon 100 octane at every fill-up if you want all those parts to make anything more than noise."

This may explain the differences that a lot of us feel at different times. Sometimes the car wants to scream and other times it feels slower. Here is the link to the entire article. It may be a repost, but some good info nonetheless.

http://www.sportcompactcarweb.com/ro...0405scc_nismo/

 

we've driven my car on 91 w/14psi vs 101oct w/ 14psi...no difference in timing advance according to an obd2.... who knows? i was expecting to see a difference as well.