I have a 1990 300zx tt and sometimes while driving it will start to smoke white out the exhaust it doesnt do it all the time just sometimes usually after i get in to it or rev it. I did a leak down test and no bubbles seemed to be coming though the radiator every couple of days i do have to add coolant to it but it never over heats. I was wondering if it could be my turbos or is it a probably a head gasket

Under no normal circumstances do you have to top coolant off every few days, your coolant is leaking, it may be a head gasket. Turbos would be burning oil if anything and the smoke would be milky blue

The leak can be from a LOT of places, check all hoses and connections carefully. I have been tracking a similar issue with mine and it seems to be the heater core being able to allow a small amount of air into the system after a day or two, or hot days...a possibility for you as well. You can loop the heater core out of the cooling system with a another hose to check that. I've had to do the core on my old NA years ago, it's (heater/rad core issues) a fairly common problem as the cars age.
Hope this helps.

What does the smoke smell like? Coolant, oil, and fuel all have very distinct smells to them when they're burning. I'd bet you're burning that coolant in some capacity if you're having to top off the radiator. Either that or you have multiple issues (i.e. a leaking coolant system combined with a blown turbo)

It has a burnt oil smell to it but the smoke is white. Also i did a combustion leak test and it came out good also i never have to add oil to it

Burnt oil smell is gonna typically be burnt oil. Pull your intake hoses off your throttle bodies and see if there's oil in the piping. If so, blown turbo seals for sure. Are you sure it's coming from the tail pipe 100% or is it just coming out the back while hammering down, and goes away when you let off the throttle? If just billowing out the back while under load, you may have a leak on one of the turbo oil feed lines or drains that's dripping down and burning on the precats/downpipes while the oil pressure is up from high load.

What mods do you have done to intake/exhaust/turbos?

Has mines chipped ecu 2.5 in cat back exhaust and 14 lb boost. The intake pipping seems to be clean. The smoke doesnt happen all the time just usually when i drive it hard later that day it will start smoking then i can rev it to like 3k and the smoke will clear up

You're sure it's not a sweeter smell than burnt oil? Coolant will have that sweet smell. What were the results of your leakdown test?

The leak down test came out good also the smoke it self doesnt smell like oil or sweat it just smells like exhaust but there is a burnt oil smell that i think is coming from a leak