Here are instructions for creating a simple electronic overboost shutdown eliminator. (NOTE: this setup is designed for those who want to run no more than 14psi of boost.) It also has the added function of a turbo response kit--the wastegate will no longer begin to bleed off pressure until your peak boost level is reached. While this setup will not actually create any more peak power compared to already running 14psi of boost, it will create more low-to-midrange horsepower and cause your car to accelerate more quickly and consistently.
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. Permanently mount a solenoid underhood as close as possible to your vacuum source and the wastegate actuator.
3. Get a new rubber line and connect it from the intake manifold (or turbo output barb) to the on solenoid barb. Then immediately cut this line in half and reconnect it with a vacuum tee. For the moment, leave the last barb of the tee empty. Now take another length of rubber line and attach one end to the wastegate actuator's hose barb; plug the other end onto the center solenoid barb.
4. Get a quick-release 12 volt pressure switch that is calibrated for 14psi (such as NAPA's adjustable one, part number 701-1577). By definition, "quick-release" means one that will quickly turn off once its feed pressure drops below 14psi--hopefully within 1psi of 14. If your pressure switch doesn't shut off until pressure goes below 6psi, for example, then you need a better one. Connect the pressure switch's barb to the open barb on the vacuum tee in step #3.
5. Finally, connect the electrical wires. Attach one wire from the solenoid to a clean ground. Connect the other one to the electrical output wire from the pressure switch. Lastly connect the pressure switch's electrical feed line to a reliable 12 volt line (adding a small fuse is a good idea). That's it, you're done!
What have we done? We have bypassed the computer's wastegate solenoid altogether. The wastegate itself operates on the pressure 'fed' to it by the wastegate solenoid; it uses this pressure open the wastegate (which is spring-loaded closed) just enough to regulate boost. However, the computer is programmed to start opening the wastegate as soon as boost is created; by 3 or 4 psi the wastegate solenoid begins to slow down the rate of boost gain even if you are at WOT.
Our setup is different. We don't let the wastegate see any pressure until the desired peak is reached; at that point the full amount of pressure is suddenly released to the wastegate, allowing it to open. This would instantly cause our boost level to drop, but we are using a quick-release pressure switch that instantly shuts off once pressure drops below 14psi. With the pressure switch off the solenoid also turns off and the boost level begins to rise again; the process repeats itself over and over, indefinitely holding approximately 14psi of boost until we back out of the throttle. Tah-dah! Bet you didn't think making your own wastegate solenoid setup was so easy.
Modified 6/24/00.