boost pressure

is there any way to change the spring on the stock wastegate to allow higher turbo pressure?

yeah... it's called a manual boost controller... google it

yeah i found the one on AMZ for $35... does that valve have any labeling on it to tell max boost? and also, for daily driving, how much boost could i run safely on a 63,000 mile no-leaks engine? (87 z31) i know a lot about cars and how to work on them, hell, i work at a customs shop. just wondering about the specifics of this particular car.

buy a quality boost gauge, 8psi for daily driving, 10 psi for cool nights for short periods of time... if you want to go more you'll need to get an intercooler and fuel upgrades

The turbo in the Z31 maxes out at 15psi. I would only recommend this as an option for short bursts on cool days. You can run 8-10 psi reliably on a daily basis.

If you buy a boost controller, you MUST buy a quality, accurate boost gauge.

15 psi on stock injectors is suicide, i wouldn't go more than 12.5 psi AT MOST