10-12psi is the upper safe limit and even then you're pushing it. If you want to go higher safely, stud the heads. X2 on the truck, she's a looker.
The thing about going higher on the boost with that particular turbo is that she starts heating the air up something fierce, without an intercooler you'll lose more than you gain. The system was designed with the high compression ratio that the IDI has, so it was not meant to boost real high. The turbo gets pushed out of its sweet spot and makes the egt's go up. Not a good thing unless you feel like melting the old girl down.
Take a look at the stickies, and use that as a primer about the do's and don'ts when boosting these things on a stock longblock. A lot of the people that participate here have been there, done that and have the broken parts to prove it. Can spare you a lot of expensive mistakes.
1. These engines are great if you don't try to make them run like a PSD.
2. They are limited fuel wise in stock configuration. There are things that can be done to
improve the fuelling and the timing; Agnem has a pump program that makes these
engines run a lot better.
3. To really go big on the power will require a full on build, a lot of custom parts. Since
there isn't a lot of support for these engines, ya gotta do whatya gotta do.
The safe way to put large boost into this engine is to decompress the motor, maybe alter the cam timing since it goes hand in hand.
If you need to know anything, don't hesitate to ask, that's what we are here for.
sweet looking truck you got there.
