[Koji_Online]

Japanese & US have different ways to rate octane. 91here is fine & the scion ECU was most likely tuned this way when it left Japan. 100 octane is at select rebel gas; another thread here has talked about how cars perform best for their tune on a certain octane. You will gain no benefit from 100 unless you get tuned for 100

I highly recommend you use chevrons 91 w/ techron though; my previous car RSX-S was ecu tuned & highly sensitive to gas from different stations. The car never knocked with chevron, while it did with others; just my experience sharing =P