Here you go, from IPD
BASE WASTEGATE ADJUSTMENT 850 / 70 SERIES
It's not possible to change the maximum boost level w/o check engine lights, but you can adjust the base wastegate setting to improve bottom end throttle response and torque. The base setting is about 1.5 psi, you can safely raise this to 5-6 psi. This will significantly improve off the line throttle response. If you over do it, you will have a hard time preventing the tires from spinning on take off so you might have to experiment a bit. You'll need a boost gauge or other accurate low pressure gauge that you can temporarily use to adjust the wastegate. We use a radiator pressure tester / pump that has a built in gauge. You can get these for around $50 or borrow one. Remove the heat shield above the turbo, disconnect the wastegate actuator line at the turbo controller valve (TCV) and attach the pump and gauge to this line. Make sure your connections are tight, you don?t want any leaks to cause erroneous adjustments. Disconnect the waste gate actuator rod form the waste gate lever (C-clip or spring clip). Loosen the 10mm lock nut and shorten the rod so that it exactly lines up and drops over the closed waste gate lever when 6 psi is applied to the actuator. Test and adjust to suit your personal tastes. Do not exceed 8 psi, it won't hurt anything, but performance will be reduced and you will get a check engine lamp as the ECU is sensing that the wastegate is operating beyond the control range of the TCV.
Be careful not to overboost at too low RPM, the Con Rods may get pissed off.
Wills