What is the best full synthetic oil for a 1991 Nissan 300ZX?

any of the castro synte for Nissans.

Any full synthetic will do good. Get the manufacturer's suggested viscosity grade most likely 5W 30 or 10W 40 and purchase on price.

All oil is the same as far as brands go I sell oil on a daily bases I work in the vehicle department be sure you get the right viscosity

The Best oil Available today is MOTUL It takes heat away better than any oil on the market. Next best AMS OIL Then the commercial brands for your car go to Walmart and get 4.5 qts Mobil one 10/40

ROYAL PURPLE all the way. 10w40 for warm weather 10w30 for cooler.
I got it in my z31T in the engine, transmission, and rear diff. It give a little extra kick also. Malwart do not sell this stuff, but a performance shop should carry it. Ebay has some also.

cardomain.com &gt, musha_man9 come check out my Z31.

I've generally told my customer's to use Mobil one full synthetic. The older the car, higher viscocity ranking. I have been using them in all my cars from my race cars to my daily driver and I have NEVER had an oil related failure in all of my cars. Great for performance driving, great for racing, great for driving to work.