I picked this trick up from a bright guy on the JYTurbo mailing list. This is a useful modification that allows you to get LOWER boost from your turbo system.

Using the stock wastegate actuators that come on Ford Thunderbird Turbocoupes, I was seeing 10psi boost. I wanted more like 6-7psi so that I could run 91 octane pump gas without worries. Even an occaisonal 87 or 85 octane could be possible if I could get the boost low enough. This modification will allow you to run almost any pressure lower than than the base setting.

In the near future I will install an electronic controller to raise the boost above the base setting. This system will limit boost to a safe level if detonation is detected through its block mounted knock sensor. The initial setting of the wastegates will need to be low enough so that detonation will never occur at this setting. Then the electronics will be able to regulate the boost up to the boost level the fuel can handle.

Here's the modification. Click on the pictures to get a bigger version.

Cut the end from rod and thread several inches of it. I used a 1/4" x 28 die.

After threading the rod and end, I collected these parts to assemble the adjusters.

A couple more shots.......

Here is the assembled unit being tested with a guage and pump. I used to see 7 psi when the rod started to move. Now it moves at about 4.5psi.

At 10 psi you can see the rod has extended quite a ways. It keeps moving beyond this but the guage is maxed out. The movement seems linear with increasing pressure.

You can easily adjust the spring preload to alter the boost level. I chose a somewhat soft spring that would have a long range of motion without becoming slack. The spring pressure will be more constant across the small motion of the wastegate opening. My thinking was that the wastegates could open quicker with less boost this way. You can do the spring rate calculations, but the result is it should take a smaller range of pressures to modulate the wastegate from "fully closed" to "fully open". Hopefully this will give a steadier boost level without spiking. The springs are easy to change and can be swapped out to change the boost curve.

I'll update with some results on how they work later.
-Ken

Thats all folks.....