Hero of turbo Dodge owners everywhere, Gus Mahon had mentioned the use of a Grainger valve (so called because he purchased them from Grainger; other shops sell similar pressure regulating valves) to control boost. After hearing him explain the procedure, I decided to try one out and see how it works. The results are so pleasing I decided to make my own page showing you just how to set one up.
To start, buy the right brass pressure relief valve: Grainger part number 5z763. (The same valve is also available from McMaster; ask them for part number 48935K25.) Grainger typically sells only to businesses, though, so you may need to do this through your work or some other creative way. I was lucky; my dealership has an account there so I could just drop their name, pay in cash, and off I went.
Once you've got the valve, it's time to modify it to suit our needs. You'll see it is a simple two-piece design that screws together and has a lock ring to hold it in one position. Inside you'll find a spring and a steel ball. Remember those high school physics lessons about springs and their resistance? You're about to love that whole principle!
Begin by seperating the halves. As packaged from Grainger, the ball is on the knob end of the valve (just like in the picture above). You want to take it out, put it at the threaded end (with the red thread sealant), reinsert the spring and then screw the halves back together. The threaded end will serve as our pressure inlet, so that's why the ball needs to be at that end.
Now you need to gather two or three more items: a 1/4" brass insert and a 3/8" brass barb fitting. I always buy these at Home Depot. Sometimes I am unable to find the correct female barb fitting. If that is the case, don't panic: just buy the male barb fitting and a female-to-female brass coupler. It will still work perfectly.
Here is a male barb (3/16" ID, approx 3/8" OD) fitting, Watts part number A-96:
And here is the brass coupling, Watts part number A-732:
Don't panic about having to buy all these pieces. Even if you have to use a coupling as shown above, this entire operation will cost you under $20.
Now that you have all the pieces, assemble them so the hose barb is attached to the threaded end. Once it is together it ought to look something like this:
Now you just need to install the whole thing underhood. The first step is to completely remove your stock wastegate control system's vacuum assembly from the car. On a blow-through setup, the stock pressure feed source for wastegate control is a barb on the compressor housing of the turbo. Remove the vacuum hose from that barb, plus the vacuum line from the hose barb on the wastegate actuator (the tuna can looking thingy). Also remove any vacuum lines, t-fittings, and whatever else you find in the vacuum lines between the turbo's barb and the actuator's barb. There will be one vacuum line that goes across the engine bay right behind the valve cover, then wraps around to the wastegate solenoid. If you don't want to dismantle your vacuum harness simply to remove this one hose, you can leave that line open and hanging there--it will no longer see vacuum or pressure so it doesn't matter.
Once all the hoses are gone, you're done removing things. In other words, do not unplug or remove the wastegate solenoid from the car. If you unplug the solenoid, the computer will be upset and will illuminate the 'check engine' light as a result. But if you leave the solenoid connected, the computer will remain happy. Got it? Good.
After you have removed all these hoses, you're ready to install the Grainger valve. Attach a new vacuum line to the barb on the compressor housing, run the hose upward toward the brake booster and attach it to the barb on the valve. I usually route the hoses so the lines loop over the fat vacuum hose that connects the intake manifold to the brake booster--this way the valve doesn't fall down onto any hot engine pieces, plus it is easy to reach for making adjustments.
Now we need to install the vacuum line on the other end. Using another new vacuum hose, carefully measure how long the hose needs to be to reach the actuator's barb, then cut it to length. Don't install it yet. Instead, set this hose aside. Now remove the knob end of the valve--make sure you don't drop the spring or the ball inside the valve! Once you have the knob end free, take it and the hose to your workbench.
Installing a vacuum hose onto the insert seems tricky. My tip is to use a short Phillips screwdriver and carefuuly apply pressure to the insert from the inside of the knob end. Then it will be easy to slip the vacuum line onto the outside of the insert. I usually then install a small zip tie very snugly to "clamp" the vacuum hose onto the insert. Now think about the other end of this vacuum line--will it fit on the actuator's barb fitting? It might not. You may need to scrounge up a straight vacuum adapter (or maybe a vacuum tee with one large barb and one small barb--cap the remaining unused barb) so as to connect to the actuator. Once you have it all set and ready to go, there is one final step: drill a very very small hole in this vacuum line--I'm talking no larger than 1/16" in diameter. Make sure the hole is located on a spot of hose that isn't covering any hose barbs; you need this hole to allow residual pressure to escape from inside the hose.
Once the tiny hole has been drilled, install the rest of the valve on the car. Don't forget the steel ball and the spring, and remember to insert the ball toward the threaded end. When you're all done, it should look similar to this:
Now for the fun: dialing it in! To begin with, leave the brass valve just barely screwed together and go for a short WOT run. The boost level will rocket to a certain amount, then instantly settle there. If the boost level is less than desired, just shorten the valve a bit. (Since the brass insert can spin freely inside the knob end, it is very easy to adjust the length of the valve without having to remove either of the vacuum lines--just loosen the lock ring, adjust the valve, then tighten the lock ring.) With a little trial and error, you can dial it in very near your car's cutout point; once there, you'll never have to fiddle with it again. Set it and forget it!
I think it goes without saying, but just in case: installation of this valve requires the good sense to manually monitor your air/fuel ratio. Since we've taken control of the boost level, the computer can no longer do anything about it. At the very least, be sure to install a Cyberdyne gauge and pay attention to it. Reading your spark plugs after the dial-in procedure is also a good idea--avoid detonation at all costs!
Modified 2/26/09.