You can back off the timing to run 87 octane. You won't get the full benefit of the tune though.

 

As touched on above, I believe the predator only allows for a 3% change. It needs to be reprogrammed so you have some tunability. I really believe diablo does this on purpose. If you can run 93 octane gas, n/a, you can run a lot more total timing that 14. As a matter of fact, new Saleen mustangs recieve the Saleen powerflash ecu, and the total timing is set fairly high, around 22.