Is high test really necessary?

Jordo!

91 is fine.

I'm saying that yes, it is possible to run a high CR piston on octanes < 91, provided the spark advance tables are properly tuned for it, but no, the Z was -- at least according to Nissan -- not tuned for it.

Also, there are indeed special considerations for octane needs unique to the design of higher compression pistons, and it is unknown (or at least not widely known) how the VQ37HR pistons behave in terms of hot spots under load.

So, I'm agreeing with you, but calling attention to the potential unique needs of higher CR pistons, in much the way that Sh0velman was pointing to potential exceptions associated with running motors at higher altitudes.

I don't know how much of a role the piston crown design and specific CR is playing a role in octane needs for the Z's motor relative to the tune alone, but it is indeed possible.

I do know this tho': In the owner's manual it says some light knock when chugging up hill is "normal"...



That alone tells me this motor prefers higher octane fuel.

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