I'm pretty sure it has to do with the engine and the compression ratio...If you have a Z, why not put the best in it...(Premium Gas, Synthetic Oil, etc).
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Daily Driver: 2010 Magnetic Black Nismo 370Z #400 (Nismo carbon fiber shift knob, Parrot bluetooth system):
Track Car: 2010 Nissan GT-R Premium Black Obsidian (546whp 568wtq)
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