Figure 1:
Pop-Off Valve Location
Figure 2:
Setting Template
Figure 3:
Marking Center of Hole
Figure 4:
Drilling Hole
Figure 5:
Drilling Hole
Figure 6:
Pop-off Valve Hole Drilled
Figure 7:
Test Fitting Pop-Off Valve
Figure 8:
Applying Epoxy to Valve
Figure 9:
Applying Epoxy to Airbox
| | [The pictures in this article are of an airbox that was removed from the engine for clarity in illustration. It is not necessary, nor recommended, to remove the airbox for this procedure.] The pop-off valve, which is also called a backfire protection valve, is a good modification for 911s with the Continuous Injection System (CIS). In the event of a backfire, which is not uncommon with these cars, the force can crack the airbox. A cracked airbox will prevent the engine from starting, as it creates a massive intake vacuum leak. The airbox is expensive, and takes several hours of labor to install. Replacement of the airbox at a Porsche dealer can easily top $1,000. The pop-off valve allows backfire pressure to escape harmlessly through the air intake. This easy modification will protect your 911 airbox from costly damage. The pop-off valve kit includes the valve and a drilling template. You will also need a two-inch hole saw, a right-angle drill, and special epoxy adhesive. In choosing the hole saw, one with a long pilot drill, or one that is adjustable if preferable. If the pilot drill is too short, the hole saw teeth will contact the ribs in the air box floor first making drilling more difficult. To begin installation, remove the air filter. Carefully position the template in the bottom of the airbox, and drill the hole. (Figure 1) Note that the arrow on the template should be centered on the screw, regardless of whether the template touches the left wall of the airbox. (Figure 2) You may wish to mark the center of the hole to be drilled (Figure 3), and drill a smaller pilot hole to prevent the hole saw from moving around. (Figure 4) Make sure you hold the drill bit vertical while drilling the hole. (Figure 5) Vacuum the plastic chips from the airbox, and from the hole as best you can. Any tiny chips left will be drawn into the cylinders and burned. (Figure 6) Test fit the valve into the hole. (Figure 7) It may be too large initially. If so, lightly sand the valve to reduce its circumference until it is a snug fit, and can be pushed all the way down, flush against the ribs in the bottom of the airbox. Once you are satisfied with the fit, take the valve back out, and proceed to glue it in place. Ensure that the area around the hole in the airbox in clean, and free from any oil or gas. Mix the epoxy well, and apply it to the lower part of the circumference of the valve, where it will seat in the airbox. (Figure 8) Apply a thin coat of epoxy to the inside edge of the hole in the airbox as well. (Figure 9) Install the valve into the airbox, rotating it slightly to ensure that the epoxy is spread completely around the valve. Note that the hinge of the valve must be oriented on the side nearest and parallel to the rear bumper. (Figure 7 again) Put a tiny dab of epoxy on each end of the valve hinge pin to ensure it does not come loose. Let the epoxy cure for at least 24 hours. Make sure that the valve can be opened, the O-ring is seated, and that the spring holds the valve closed properly. Reinstall the air filter, and you are ready for driving your car without worry of backfire damage. When you do the routine maintenance on your car, it is a good idea to inspect the O-ring in the pop-valve to ensure that it is in good condition.
A random customer added: A tip, for your tip catalogue? I was having hot start problems , and I found that my popoff valve "o" ring was not seated well in the slot (inside air box) and was allowing a vacume leak, hence , no start, but would start well cold with the help of the cold start valve, kinda wierd , but thought I'd pass it on anyway |
