Once you've experienced the joy of using a grainger valve, the next logical step is to add another. Sound complicated? Not at all! Read along and see how simple it is.
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. Acquire two grainger valves (Grainger part #5z763), two brass threaded female hose barbs, two brass barb inserts for the hole in the knurled knob end of your valves, one stock 3-barb solenoid, a vacuum tee, the SMALLEST drill bit you can find, plus some surplus vacuum hose and a few zip ties.
2. Mount the solenoid underhood as close as possible to your vacuum source and the wastegate actuator. On the firewall near the brake booster, for example.
3. Prepare your grainger valves for pressure relief by moving the ball to the red threaded end. Attach the brass female threaded hose barbs to each valve, then install the brass inserts such that they poke out the holes of the knob ends of the valves. TIP: when you install these inserts, hold them in place internally with a phillips screwdriver and then attach vacuum line to the protruding tip. The friction of the hose will then hold the insert in place, allowing you to reassemble the valve. To ensure maximum clamping power, I usually install a zip tie to this vacuum line when I'm done.
4. Using more vacuum hose, attach one grainger to the off barb of the solenoid, then connect the other grainger to the on barb. NOTE: you're attaching the fancy threaded barb end, not the little tips you just installed in step #3.
5. Now take both tubing ends which are attached to the little tips and install them onto two barbs of a vacuum tee. Keep these tubes short. For the last connection we will simply use a chunk of hose to connect the open vacuum tee barb to the wastegate actuator barb, but before you do so you must use the TINY drill bit and make one hole in one wall of this last piece of hose. Make this hole so small you can barely see it, and make sure it is positioned such that it will not be blocked by the actuator barb or the vacuum tee barb when you install it.
6. Finally, connect the electrical wires. Attach one wire from the solenoid to any convenient switched 12v source. Run the other solenoid wire to a toggle switch mounted inside the car; run the remaining toggle switch wire to any solid ground connection. That's it--you're done!
Now you need to dial in the grainger valves; we do this like with one grainger valve. Leave your toggle switch in one position and adjust its valve such that the maximum boost level is where you want it, then flip the switch and adjust the other valve in the same manner. (For maximum safety, I suggest you begin with each valve open all the way, then gradually close in until your desired setting is reached. Don't forget to check your plugs and verify proper fuel delivery!) Now you have two-stage boost control at your fingertips, and you can switch back and forth as often as you like at any throttle position.
What does a two-stage setup do for us? We can set low to give as much power as the tires can handle without spinning wildly, and we can set high as far as our fuel system, engine and nerves can handle. (Seriously, do not try to run more boost than your fuel will support--your engine will thank you for it.) Hey--tuning a supercharger was never this easy! ;)
Modified 6/25/03.