This is a really easy, free modification which lowers engine oil temperature 10-15 degrees F. It is applicable to all 911s and 914-6s built before March, 1977. That's the good news. The bad news is, in order to get at the cooling deflectors and their retaining clips, you must remove the alternator, exhaust manifolds, engine cooling shroud, and oil return tubes. This modification is easiest to do during an engine rebuild.
The modification consists of cutting a 1" wide strip out of the four middle cooling deflectors (see photo 1). This allows air to circulate more freely around the cylinders, making them run cooler and reducing the probability of pulling head studs. The strip you cut out runs along the outer edge of the deflectors. It starts at the top edge, and ends a small distance above the crease where the legs of the deflector spread out in a "V". That distance (dimension "A" in photo 2) is 1/2" for normally aspirated 911s, and 3/8" for 930 turbos. The outer four cooling deflectors don't get modified.
Lay out your cuts with a felt tip marker before reaching for the tin snips. Never scribe a line on sheet metal unless you intend to cut along that line, because a scribed line creates a huge stress riser which encourages cracking. The air deflectors are not highly stressed parts, but I drilled a 1/2" hole in the corner of the cutout because I hate sharp edges and the stress risers they create. The factory bulletin does not call for the radiused corner, but it can't hurt. Snip out the sheet metal with tin snips or aircraft shears; the deflectors are thin and easy to cut.
Smooth off your cuts and all other sharp edges with a fine file or 240 grit sandpaper. Breaking sharp edges makes the paint stick better, and reduces the possibility of cutting your fingers during handling. Repaint or powdercoat all the engine tin while you have things disassembled, and your engine room will look great!
Photo 1:The engine cooling deflectors as assembled in the engine. You will cut 1" strips from the outer edges of the four middle air deflectors. Hint: Don't use your wife's good bath towels to photograph greasy engine parts!
Photo 2:Here's the layout for your cuts. Distance "A" is 1/2 inch for normally aspirated 911s, and 3/8 inch for 930 turbos. I painted this deflector gray to make it easier to photograph. Painting the engine tin gray doesn't make it work any better. Neither does painting your brake calipers red.
Photo 3:The completed modification. Round off all sharp edges with a fine file or sandpaper. That reduces stress risers, makes the paint stick better, and eliminates cut fingers.
There you have it. It's really quite a simple job. If you have any questions about the procedure in this article, feel free to
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This is how the cooling deflectors and clips are assembled in the engine
The shaded area is removed from the four middle cooling deflectors. Smooth off sharp edges!
A modified deflector. Distance "A" is 3/4 inch for normally aspirated engines, and 3/8 inch for 930 turbos.