Here are instructions for creating a two-stage bleed setup which also prevents overboost shutdown. Two-stage boost control gives you the option of launching on low (normal boost) to keep the tires from spinning; once underway you then switch to high for maximum power. Launching on high will spool up your turbo quicker than normal but this will require lots of traction to prevent wheelspin. If you want really quick spool-up, you can use a smaller than stock restrictor.
NOTE: all the safety warnings found in Recipe B apply here as well. Pay attention to the gauges you've installed, be sure to read your plugs after getting dialed in, and so on.
Here's the dirt:
1. Remove the vacuum hose coming out of the wastegate actuator and plug it. Find a source of manifold pressure/vacuum (at the turbo's output barb if your turbo has one, or else from the intake manifold itself).
2. Get a pair of solenoids and mount them underhood as close as possible to your vacuum source and the wastegate actuator.
3. Get a new rubber line and connect it from your vacuum source to the off barb of solenoid A. Then cut this line in half and reconnect it with a restrictor. Next, cut the line in half again between the restrictor and the solenoid and insert a vacuum tee. To the last barb of this tee attach a short length of hose; at the other end add a check valve (being sure that air blows out from the tee, not back into it). With another short length of rubber line connect the open end of the check valve to the center barb of solenoid B. Using short pieces of tubing attach a bleed valve to both the on and off barbs of solenoid B.
4. Cut the original vacuum line (the one going from the vacuum source to the restrictor) in half and reconnect it with a vacuum tee. Add in another piece of vacuum line from the remaining barb of the tee to the on barb of solenoid A. Then cut this last piece of line in half and reconnect it with another vacuum tee. Lastly, connect the remaining barb of this tee to a quick-release 12 volt pressure switch that is calibrated for 14psi, such as NAPA's adjustable one (part number 701-1577). By definition, "quality" means one that will quickly turn off once its feed pressure drops below 14psi. If your pressure switch doesn't shut off until pressure goes below 6psi, for example, then you need a better one.
5. Finally, connect the electrical wires. Attach one wire from each solenoid to a clean ground. Connect the remaining wire of solenoid A to the pressure switch's output line. Lastly connect the pressure switch's electrical feed line to a reliable 12 volt line and run the last line from solenoid B to a switch mounted inside the car (adding a small fuse to these two power lines is a good idea).
Now you need to dial in the bleed valves; we do this like in Recipe B. Leave your in-car switch in one position and adjust its bleed such that the maximum boost level is where you want it, then flip the switch and adjust the other valve in the same manner. Now you have two-stage boost control at your fingertips.
What does all this do for us? We've got the benefits of a two-stage setup without the possibility of hitting overboost shutdown. We can set low to give as much power as the tires can handle without spinning wildly, and we can set high to just under 14 psi without bumping into cut out.
We can now use a smaller than stock restrictor, or even two restrictors right in a row, to spool up the boost quicker than normal without huge spikes. If a Zener diode or MAP bleed is used to raise cut out, a high spike could go REALLY high without this anti-spike setup and cause disaster. With the anti-spike setup, there's no way to boost too high by accident; peak boost won't go above where you set the pressure switch.
Modified 6/24/00.