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C2/C4 Primary Muffler Bypass Pipe Installation
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Pelican Technical Article:

C2/C4 Primary Muffler Bypass Pipe Installation

Tom Sharpes


1-2 hours






Floor jack, jack stands, wheel chocks, safety glasses, metric hex wrench set, metric socket set, metric wrench set, towel, Liquid wrench

Applicable Models:

Porsche 964 Carrera 2 (1990-94)
Porsche 964 Carrera 4 (1989-94)
Porsche 964 RS America (1993-94)

Parts Required:

Primary muffler or stainless steel 3-inch bypass pipe

Performance Gain:

A freer flowing exhaust equals more power and more exhaust noise

Complementary Modification:

Replace the secondary muffler with a bypass pipe as well

There are a number of opinions as to which is the most effective exhaust mod to make to the C2/4's. From replacement of the complete system with an aftermarket header and muffler to replacement of either or both the primary and secondary muffler. You choice will depend on money and desired effect.

For me, this is not a performance mod for racing - I was looking to free up the exhaust path and provide a nice sounding exhaust without irritating the neighbors. You might call this an enthusiast's modification.

I choose to replace the primary muffler (the one across the rear of the car under the bumper) and leave the Cat and secondary muffler in place.

thumbnail Place the car on jack stands or ramps because you will need a lot of clearance to move around underneath the rear of the car.


There is a pan under the engine area of the C2/4's for decreasing the noise level from the engine. Remove the bolts from the pan.

After removing the pan you will have clear access to all of the engine area.

You may want to leave this pan off in the future. Some recommend it as a way to provide additional cooling to the engine and easier access. I left the pan off of my car because it did seem that all of the sound deadening material could insulate the engine a little too well and certainly increase case temps if nothing else. I did not notice an increase in the engine noise after I finished this project but then the exhaust is louder as well.

thumbnail With the pan removed you have access to everything. The primary muffler is the one across the back of the car under the rear valence.
thumbnail The connections are not the flange type you may be used to seeing under a car. These connections are know as V or U band clamps and utilize a hard gasket ring as the mating and sealing device. On the left is the inlet connection to the secondary muffler on the passengers side with the tailpipe exiting on the right side.


Remove the bolts on both ends of the primary mufflers clamps. With the bolts removed carefully spread the band ends apart and slide them towards the Secondary or the Cat leaving them on the pipes.

Using a metric hex wrench, remove the bolts securing the muffler band clamps and pull them off completely you will not be using them for the installation of the bypass pipe.

After removing the straps just pull the muffler out from under the valance. It is heavy so be ready. With the muffler removed to can see the out let from the Cat and the inlet to the secondary muffler.
thumbnail The new stainless steel 3" bypass pipe ready to install.

Place the pipe up into the area under the valance ant rest it against the inlet and outlets of the other two pipes. Insert the hard round gasket between the pipes, slide the band clamp around the connection and install the bolt. Snug up the bolt just enough to hold the pipe in place while you do the other side.


Install the stainless steel straps around the pipe and mounting bracket on the main part of the pipe and tighten them up so the pipe is secure. Go back and tighten up the band clamps on the pipe connections.
  Start the car and place a towel over the exhaust outlet listening for any exhaust leaks coming from the band clamps - retighten if necessary. You may find you have to rotate the clamp a little around the pipe to achieve a leak tight seal.

After driving for a few days check the seal again with the towel and tighten a final time if required.

Enjoy your new exhaust sound and a more free breathing engine. If you find this exhaust is not as free (loud) as you would like it - the secondary muffler can be removed and a bypass installed in that position as well.

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Comments and Suggestions:
Gazzz999 Comments: I just noticed this technical article. Sounds good but it appears the muffler bypass pipe mod only applies to the 964. Is there anything similar for the 993 '95 C2?
November 28, 2014
  Followup from the Pelican Staff: Not that i am aware of.

I opened a post in our forums. A Pelican community member may be able to answer your question.

- Nick at Pelican Parts
gazza Comments: I bought a 964 with this mod and its too noisey for me have just fitted 10" ss resonator much more pleasant
July 4, 2014
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
KB Comments: I'm tempted to try this modification. Being in Ca. will there be "Smog" inspection issues?
February 23, 2012
  Followup from the Pelican Staff: I think there would be. I would ask a local Smog mechanic. - Nick at Pelican Parts  
Mike Comments: I have a 91 C2 and would like to know where I can get the bypass pipe mentioned.
November 14, 2010
  Followup from the Pelican Staff: Here's a link to the product in our catalog: http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait=N&make=POR&model=911L§ion=EXHprf&page=2&bookmark=10&part_number=FAB-993-CB-01 - Wayne at Pelican Parts  
tt Comments: I have a 1990 964 c4. I have a cat bypass and wanted to add the Schnell Elite Primary Muffler Bypass Pipe. Will my car be really noisy? I want to lose the weight of the heavy muffler in the rear.

August 30, 2010
  Followup from the Pelican Staff: I'm not familiar with that particular product, so I can't really give an opinion on it. - Wayne at Pelican Parts  
martin964 Comments: great writeup!I just fitted my cup pie, and the hardest part was sliding out the original. you just need to remove the sealing ring from the final silencer to give you some space. you then slide the silencer out to the right so that you do not have to remove the Cat bottom shield.
January 24, 2010
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
Jay Comments: Can I ask how this affected performance specifically low end torque? Thanks.

December 18, 2009
  Followup from the Pelican Staff: I don't have any numbers, but I can't imagine that it decreased performance. There was probably some small increase over the range. - Wayne at Pelican Parts  

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