This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.
It's quite common for the engine compartment sound mat to deteriorate and fall apart after many years of use. The design that Porsche used consists of a mat that is made of a sponge type material. This material often falls apart, leaving sponge remains all over the inside of the engine compartment. Replacement is easy, and made even easier with the engine out of the car.
The first step in replacing the mat is to remove the old one. In most cases, this will not be too difficult. The older mats have a tendency to easily pull away from the glue that originally held them to the rear of the engine compartment. If you don't have the engine or fuel injection removed, then this task will be a bit more difficult. Remove your air filter housing for more access before beginning. It's ok to rip the mat as you are taking it out. Just make sure that you cover the parts of your fuel injection (intakes on carburetors for example) that are open and susceptible to foam chunks falling inside.
The installation of the new mat is very straightforward. The key to the process is the 3M Super Weatherstrip Adhesive, which is by far one of the best glues ever created. Simply put, when you glue anything with this stuff, it sticks right away. Lay the mat out on the ground and then apply the glue to the back by squeezing it out of the tube. Creating a crisscross pattern on the back of the mat should work well. Make sure that you apply the cement to all of the edges of the mat so that they will stick to the rear of the engine compartment. If you are planning on replacing your rear decklid shocks (Pelican Technical Article: Replacing Hood Shocks), I would advise that you do that prior to installing the new pad.
The 3M Super Weatherstrip Adhesive is a fantastic glue, but it can be quite noxious. I recommend using a filtered gas mask when using the glue. Working in the engine compartment really doesn't aid in the ventilation process. The $30 gas masks available at most hardware stores seem to do an excellent job at filtering out the fumes from the glue, and certainly seems a low price to pay to avoid getting cancer later on.
For about 10-20 minutes after you place the new pad, keep pressing on it to make sure that it is making contact with the rear of the engine compartment. The adhesive will do the rest. After about 12 hours of final curing, the glue should be quite strong.
3M Super Weatherstrip Adhesive 08001 is one of those modern miracles of science. By far one of the best glues out there, its primary advantage is the way that it requires a only a minute or two of placement before it will hold things in place. It dries incredibly quickly and is easy to use. The only drawback is its overcoming fumes, which are not very healthy to ingest.
The newly installed sound pad significantly cleans up your engine compartment. Make sure that while the glue is drying, you keep pressing the pad against the back wall.