Regular Gas?

ChrisSlicks

The car is built for 91 octane, lower octane will produce knock which will cause the ECU to retard the timing and reduce power. Normally increasing octane does not increase power output as the ECU does not advance timing beyond it's preset.

However in this car it actually might. The engine computer reportedly continues to advance the timing until it detects knock. There's been reports of high octane race gas producing a measurable power boost on the dyno. How true this is I don't know, haven't been able to measure this first hand.

That said I use 93 because they don't have 91 locally.