does 87 hurt our cars? i always thought 91 was the prefered octane rating.....

 

If you are running canzoomer, I know it runs the best, with 89 octane, or so I have been told by maurice. Apparentley 89 makes the best power. (always use shell as well)
However, this may not be the case with japan spec or other versions.

 

The octane rating lets you know how well the fuel will compress without exploding due to pressure (aka knocking). Knocking is bad. High-compression cars, like the RX-8, take advantage of the higher octane fuels. However, people have been running lower octane fuels with no ill effects so far that I know of (but this might be because of the ECUs ability adjust for what the knock sensor tells it)...

http://auto.howstuffworks.com/question90.htm