All this is written up in the NADS thread, but, 22psi is a maximum safe boost for turbo and engine, but, most ZD30's can't make full use of it and if you don't have the relevant mods you will constantly be in limp.
@Jack Barns , only airflow matters. Stop thinking of "boost". Boost is a pressure. What matters are the grams of air EFFECTIVELY pushed by your turbo inside your cylinders under load, at all Revs (as measured by your MAF voltage). Sometimes I feel like preaching in the desert, but Education is repetition, even if I get more and more censured here.
In my country, the very few who have been, by "accident", running 22psi, blew up their head gasket sooner or later and/or got a cracked head. None of the others staying below 18 psi did, and after more than 20 years, are still running the same motor and the same head. I can't elaborate more about this. These are just fact ( and a simple coincidence ? Who knows really ?).
Also, beyond 18 psi, there is little gain (but there is some if your VNT is managed properly) in airflow (MAF voltage increase) with a Garett 2052. Check its efficiency map below, available on the net.
What is most important for Torque/Power is to maximize the airflow at all Revs (and down low in particular), with the least possible boost.
Last but not least, unless you have an intelligent electronic controller taking care of limp, or a remap suppressing limp, you will get limp as pointed out by Geeyoutoo, which is not nice to have.
We know boost isn't everything for gods sake, it is how you use it. I don't use the max boost I can because I don't need it, my system works fine.
Many of us have run 22psi for years without issue so I would question the source of that info, head gaskets can and do fail once you start to get over 25psi. This is fact.
Hey guys! Wanted to thank you for all the information I couldn't reply in a previous post Phil and Geeyoutoo. At least in Latin America a few months ago no one knew about NADS. I just got a Defi screen to measure everything and will give it a try to a Festo Needle valve and a manual boost controller and then hopefully try and compare Phil's creation.