Hero of turbo Dodge owners everywhere, Gus Mahon had mentioned the use of a Grainger valve (so called because they are purchased from Grainger even though other shops sell similar pressure 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, go to Grainger and buy the right brass pressure relief valve, 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. You'll also need two vacuum tees and a couple small chunks of vacuum hose.

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 is a spring and 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. See the ball and spring? Set them aside in a safe place.

Take one vacuum tee and cut off two of its barbs; be sure to cut such that the barbs are as long as possible. (Saving the third barb for the next time you modify a grainger valve is a good idea.) Now get a drill and find a bit that just matches the outer diameter of the hose barbs. Gently bore out the holes at both end of the valve so that the vacuum tee barbs will fit inside. (NOTE: use caution when drilling the end with the red sealant--drill only deep enough to allow the barb to seat properly. Drilling all the way through may prevent the steel ball from seating properly, allowing blowby.) When finished drilling, be sure to completely clean them so as to eliminate all the shavings and dust. Follow up by using rubbing alcohol to remove your skin's natural grease from the brass ends.

Now get some two-part epoxy (I used J-B Weld's new J-B Kwik fast-setting stuff--found it at Wal-Mart) and mix up a small quantity. Apply a bit to the hose barb end (be sure not to get any inside the barb!) and gently insert the barb into the valve's hole. Repeat the procedure with the other brass end, then let both pieces sit overnight to fully cure.

Once the epoxy has cured, reassemble the valve with the ball at the other end (in other words, put the ball toward the red thread sealant). Once it is together it ought to look something like this:

From here it's a simple matter of attaching a small chunk of hose to the knob end, then attaching your second vacuum tee. To one of the open tee ends attach another small piece of hose that has your stock restrictor at the other end. Now the whole assembly will look like this:

All you have to do is install the whole thing underhood. To make this as easy as possible, I just disconnected the two vacuum lines from my car's stock wastegate solenoid and attached them directly to the Grainger assembly; the manifold source feed connects to the threaded end (look at the red arrow in the picture below) while the output to the wastegate attaches at the vacuum tee. (If you've not yet done so, remove the stock restrictor in the vacuum line that goes to your wastegate--the only restrictor we need to use in this setup is the one we installed in the picture above.) Note that the restrictor doesn't attach to anything; it is left open to the atmosphere and acts as a relief for the pressure that is left in the wastegate when you quickly lift the throttle. It needs no filter since it never sees vacuum.

Now for the final 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 amount is less than desired, just shorten the valve a bit. (I unplug the source feed, loosen the lock ring, adjust the valve, tighten the lock ring, then reconnect the feed line.) 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 cannot do anything about it. Be sure to install a Cyberdyne gauge and pay attention to it. Reading your plugs after the dial-in procedure is also a good idea--avoid detonation at all costs!

Modified 5/21/03.