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Any current production car that's out there made by Nissan has a knock sensor, regardless of turbo or not. The tune the ignition and fuel mapping around 91 octane fuel for best performance and fuel economy. They can run more ignition advance and slightly leaner.
Now when you put 87 octane into the car, the knock sensor is going to tell the ECU to retard timing. If the ECU still sees a lot of activity from the knock sensor, it will switch to a low octane map and retard the timing and richen the mixture. On a Z32 it also lowers the boost pressure. It will stay on the low octane map until you cycle the ignition switch.
Since Nissan doesn't sell and turbo cars in the US at the moment, I can't say what their recent thinking is. On Nissan's current engines it is more aggressive about switching back to the high octane map and will try to do it without cycling the key.
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