None of the factory euro pre-mufflers I have seen have any form of packing. They all consist of a straight through partially perforated tube (the same diameter as the outlet) that goes from the merged inlet pipes to the just short of the outlet flange (about 1" short). The perforated tube is held in place by a collar between it and the larger diameter casing. This collar is located about 2/3 of the way along the casing and also has perforations in it. Here are some pictures of a standard equipment Gillet pre-muffler.

http://i226.photobucket.com/albums/d...ps04vnbou7.jpg

http://i226.photobucket.com/albums/d...ps0eopnqvb.jpg

The internal pipe does line up with the exit flange, I have angled the camera to show the gap, collar and perforations which makes it look out of alignment.

One of the advantages of changing to a pipe is a reduction of weight at the back. The pre-muffler weighs just over 13lb, the pipe in the picture below weighs 6.5lb. I guess the weight saving over a catalyst would be greater.

http://i226.photobucket.com/albums/d...pszg2uxcwy.jpg

For the record, I felt a difference in performance between the above pipe and pre-muffler on a chipped euro 3.2, but no increase in noise level. With the pipe it felt more responsive above 4K, but it may have been just a slight shift in power band rather than an increase in power. As for noise, I have a rather loud 2 out and that may have overpowered and difference between pipe and pre-muffler.


Mark

I recently installed the fabspeed cat bypass. I little bit louder. Install was a pain. All my bolts were rusted out. O2 snapped off in the old cat. Ended up with a new O2. Lucky the Fabspeed came with new hardware. I cut and drilled the old stuff off. A few of the bolts were too close to the pipes to use a cut off wheel. I drilled those. I feel the car runs better and cooler, but probably just in my head.

Any opinions related to the M&K pre muffler versus the fsbspeed? They're both about the same price and have a similar appearance.

^^ I've owned both and while they both sound similar the M&K is much higher quality. The M&K is beautifully made and has a bare stainless finish, the Fabspeed has a polished finish which, to me, looks "blingy".

The M&K looks a little more like a cat converter as well (if that's what you're trying to achieve).

Pre-Muffler vs Bypass Pipe
 

Here is the M&K Pre-Muffler (top) and Bypass Pipe (bottom).
Pre-Muffler has a packed muffler body, Bypass is just a pipe. Both are similar performance as ID is the same.

http://forums.pelicanparts.com/uploa...1448235452.jpg


Here is the M&K Pre-Muffler and Fabspeed. M&K uses an actual merge collector and captures both banks for the O2 sensor. Material is 321 stainless and it is made in the USA.

http://forums.pelicanparts.com/uploa...1448235560.jpg

Fabspeed was running a black friday special today... 10% off. Couldn't resist :) Bought their performance package which includes the pre muffler, the muffler, intake lid, and a SW chip.

I'm not looking to go any deeper than simple bolt ons for a street car, but I did want to add some noise and smooth out the throttle response. Should be perfect.

Any black Friday/ cyber Monday specials on M&K RarlyL8??? Looking for a bypass and 1in/out.