OK for 30# peak, on a IX turbo fitted with an FP 25# WGA and controlled via a MBC, I would go about setting preload in the following manner, assuming of course that I would be aiming to optimize quick turbo spoolup and rate of spool:

Once you bolt the new WGA up to the compressor housing, loosen the backup nut on the actuator rod and adjust the hole on the turnbuckle till it freely slides on and off of the peg on the flapper valve's pivot arm. Install the actuator rod onto the peg.

Cut and install a length of hose and connect it from the compressor discharge tube(J-pipe) nipple to the nipple on the WGA. Take your car out and try a WOT run in 4th gear. The boost level indicated on your boost gauge is going to be your base WG pressure, or base spring pressure.

The method above described is the proper way to determe absolutely the base WG pressure. You can get similar results I guess by just turning your MBC knob out counterclockwise to its full soft(lowest possible boost) setting.

OK once you determine the base wastegate spring pressure with that particular WGA then you can go on to adjust the level of preload from there.

Although it is a tedious process, it is important for accurate reference purposes to empirically determine your turbo/WGA spring pressure. Eventhough FP calls their WGA 25#, or 18#, or whatever, I have personally seen a FP 18# HD actuator that actually opens fully at 14#.

 

Once you have verified your particular turbo/WGA's spring pressure, then you can procced to increase preload beyond that predetermined level.

Let's say for illustrative purposes that the actual confirmed spring pressure is 20#. Or the point where the actuator rod slides on and off the peg freely and that furthermore, you want to be running peakboost level(controlled via MBC) of 30#.


You can increase preload incrementally via 360* rotations of the turnbuckle inward(clockwise) on the threaded end of the actuator rod. Each rotation will increase spring tension by a set poundage. If each rotation results in a 1#increase then you'l need to do 4 complete rotations to get preloaded spring pressure up to 24# and etc.

I recommend going about it slowly and increasing spring pressure gradually in one PSI increments. Reinstall the arm and test after each rotation just to make sure.