North American Turbocoupe Organization

Gillis Adjustable Boost Valve
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Ric Gillis Adjustable Boost Control Valve

Installation Details

87-88 Turbocoupes, 86 SVO, earlier Turbocoupes and SVOs similar

These instructions and diagram are NOT intended to replace or revise the instructions you receive with the Gillis Valve.  These instructions are only intended as an addition aid to help you in your install.  Please read and follow the Gillis installation instructions first and foremost.

First step is to locate the components under your hood before removing, changing or installing anything.  

1. Boost Control Solenoid (BCS) is located on the passenger side inner fender near the fresh air tube from the fender well. It is cylindrical, 2" in diameter and has 2 vacuum lines going to it as well as an electrical connector.

2. The vacuum tree, its black plastic and located on the firewall near the master brake cylinder, has several ports with vacuum hoses running to it.

3.  The Waste Gate Actuator (WGA), it's a round diaphragm type device located underneath the turbocharger. It has a vacuum port on one side and a long thin rod on the other that actuates the waste gate. You will be running a vacuum line FROM the Boost Valve to the vacuum line going to the WGA.

4. The Compressor Outlet, which is attached by rubber tubing, to the bottom of the Intercooler. On non-intercooled cars it connects, by tube and hose to the throttle body on the upper intake. Note the vacuum fittings on the compressor outlet.

Determining the INLET and OUTLET  ports of the Gillis Valve.  See the diagram that came with  the valve.

The INLET port is at the opposite end from the adjustment knob.

The OUTLET port is in the middle of the valve and comes off the valve at a 90 degree angle.  

     1.  Follow the hose from the top port of the BCS to the 2 port fitting on the compressor outlet. Remove the end from the compressor outlet fitting, leave the other end attached to BCS. The other hose on the Compressor outlet fitting goes to the WGA. Remove this hose from the outlet fitting and put a straight-line connector into it.

     2.  Remove the 2 port fitting form the Compressor outlet and install the 1/8 hex plug in the fitting hole.

     3.  Follow the hose from the bottom port of the BCS to the fitting on the compressor inlet. Remove the hose from the inlet port and cap off the port.

     4.  Decide where you want to mount the Boost Valve. Mounting it to one of the bolts that holds the VAM bracket to the passenger inner fender is a good location. The VAM  is the big aluminum thing that connects, by hose, to the Compressor Inlet. The bracket that supports it mounts to the inner fender with two bolts. Mounting it here keeps the vacuum lines short while making the valve easily accessible for adjusting.

     5.  Measure the length of hose needed to go from the Boost Valve OUTLET (see valve diagram) to the straight-line connector in the hose to the WGA,  (see #1 above). Cut hose to the length needed and install on Boost Valve Outlet and straight-line connector.

     6.  Install one end of remaining vacuum hose on the Boost Valve INLET; (see valve diagram). Run the other end to any unused port on the Vacuum Tree on the firewall.

     7.  The two hoses attached to the BCS can be left attached to it. Leave the BCS in the car with the electrical connector plugged in. This is so the system can be restored to original if you ever desire to uninstall the boost valve. The vacuum ports on the BCS are kind of fragile and that is why you shouldn't try to remove the hoses from it. It is an obsolete part from Ford Motor Co. and hard to replace.                

     8.  If any of the vacuum lines are brittle, cracked or loose at connection points they should be replaced with new vacuum line of the correct size.

     9.  Adjust the valve so at least 4 or 5 threads are showing visible on the adjusting knob. Tighten the lock nut securely and go for a test drive. Monitor your boost gauge and listen for any unusual sounds (detonation). Make adjustments gradually.

Other considerations:

It's recommended to use an aftermarket boost gauge or better yet, a combination Vacuum/Boost gauge. There are a few brands available. It's better to use one that goes to 30 psi boost instead of  20 psi. Gauges tend to be more inaccurate at the ends of their scale. The factory boost gauge is often inaccurate and more so at the top end.

NATO and it's members bear no responsibility for the results of any modification(s) listed.



A simple diagram (courtesy of Gary Schweikert):

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