I'm looking to pick up a second Z31; a 50th AE turbo 5-speed; currently all stock.
(my first Z31 is currently a parts car because the previous owner is being a pain about the title)

I know the rated 0-60 time at stock is ~7.1 seconds, which is not a bad speed.
I'm not one for modifying an engine, so my car would stay mostly stock.
The only things I'd really be looking to change would be a cold air intake, and most likely a 3 inch full exhaust (no cats).

With just those two basic things, could I expect a slightly faster 0-60 time, possibly in the 6.5 range?

 

Welcome to ZDriver!

No.

But what would get you there (and faster) is a boost controller, intercooler, and 10-12psi boost.

Click: Jason's Z Site - REDZ31.NET

 

you don't need the intercooler if you keep below 10 psi. manual boost controller like 30-40 bucks. if you don't have help and tiny fingers it can be a challenge to hook up the control tubing. cold air intake a myth already on the car but lots like to put in a K&N filter - looks kewl

 

Bigger exhaust is always recommended when increasing boost, as exit air volume is just as important as intake air volume.