SC, Carrera Bischoff Muffler Modification, Mod, Gut, Gutting, Dual, Two Out

[Gordo2]

Out of curiosity I tore into a spare muffler I bought recently. It's a Bischoff 1 in 1 out muffler stamped 06/87. I believe this is the same model of muffler as was installed on SC models. My SC has an earlier Bischoff, I assume the internals are the same.

I'm goofing with this project to see what I can come up with for a 1 in 2 out configuration that gives me a healthier exhaust note. I've always thought my SC with its stock exhaust sounds weak.

I'm fully aware of exhaust options for my car; this is a "why not" kind of project. This thread is for other curious Pelican's who have considered this job.

Here's where I am so far. Cut away took about 40 minutes (I have a small compressor) and 4 cutting wheels. I used a hole saw on the end where I plan to add the second outlet pipe.



I was expecting to find the inside layout similar to one that has been previously posted as a Carrera muffler:



The inside exhaust routing is significantly different. It appears that the main difference is that the "exhaust in" pipe of the Bischoff has an end cap on the passenger side. The incoming exhaust is forced through a perforated pipe (pipe with holes) before it makes it through the muffler; there is no open path.

I'm going to re-arrange the exhaust routing to give relatively even flow to both sides. Open to suggestions on routing.

Gordo

[Gordo2]

Another picture clearly showing the capped off "exhaust in" pipe. It seems this muffler would be very restrictive.



Gordo

[mb911]

Most Mufflers that we have cut apart run off the same principle as yours with the capped end forcing the exhaust to flow through the perfereations. In fact Our mufflers do as well but a much different design

[gr8fl4porsche]

Gordo,
What modifications or gutting do you plan on doing. I may cut open my spare this afternoon which I purchased off ebay for $20 plus shipping. I am not sure what level of gutting i should attempt before finally giving in and ordering one of Ben's fine mufflers.

[Gordo2]

After a long head scratch I decided on my internal arrangement. I cut the "exhaust in" (bottom pipe) so that it dumps near the middle of the muffler. It will go through the perforated pipe that will connect to both outlets. If this seems too restrictive, I may drill a few extra holes on the inlet/driver's side "exhaust in" pipe to get more flow into the driver's side perforated pipe.



Gordo

gr8fl4porsche: I'm going the semi-hard route; modifying internal flow and adding a second outlet. Other mod's I have seen include :
-Cutting out the center section of the muffler, leaving a louder single out muffler.
-Drilling a 1/2" hole on the passenger side of the muffler and welding a outlet pipe over it for a 2 out muffler.
-The previous post of the new looking muffler with a major mod that made it a straight through (glass pack/cherry bomb) single out.

Good luck, Gordo

[Wil Ferch]

My OEM muffler ( for an 85...presumably identical to the one shown) was modded by the PO to include a right-side outlet. Was told there was some gutting involved too...but can't be certain...and the body of the muffler shows no evidence of it being cut-in-two.

Advice...go "small" on the right side exhaust pipe. A 1/2" hole surrounded by a 1.5"-1.75" exit "pipe" ( like on the left) is a good idea since a large amount of volume comes from the new-right exhaust pipe. You can always drill incrementally larger holes if 1/2" is too small.

Wil

[Tim Hancock]

Here is a link to my muffler mod I did on my '79 SC's original muffler. you will see in the photos that my end tube was not capped but was actually a 180 deg bend made out of perforated tube. It was surrounded by a wad of packing which I extracted after cutting my new second outlet. It sounds pretty good now, but the idle is a little muscle car-ish. The way I did it allows me to add a block off or restrictor plate between my tip and the muffler if I wanted to.
DIY stock muffler mod, 1 out to 2 out, SC

Here is one of the pics from the above link peering into the new second outlet hole, clearly you can see the perforated 180 deg tube.

[Gordo2]

Tim,


Is your muffler stamped with the manufacture's name (Bischoff, Dansk...)?

I read your thread when you were taking the project on. Nice work on the welding, and nice work in general. The photo showing the perforated pipe inside where you cut the hole was another muffler design that left me guessing at what I would find when I opened mine up.

Gordo

[Tim Hancock]

Don, it is marked: Bischoff 930.022 00 0578 (I think the last four #'s mean it was built in '78 as the car is a '79). I too was shocked when I opened it as I had also found various other pictures as I researched it. I intended to try it with just the extra hole and if not loud enough I intended on hacking into it further. I ended up driving it all summer as with the second outlet and am pretty happy with it. I may still install a blockoff plate if I ever take a long trip in it with my wife as she thinks it is a little loud without the stereo turned up on long jaunts. Good luck with yours and let everyone know how it sounds and post some photos too!

[Gordo2]

Hasn't taken this long, just haven't been able to get back at it. Added a little effort this afternoon.

Rough tack on of the second outlet and opened up some of the holes in the perforated pipes to let it breathe better.



Considering adding some muffler packing to the passenger side chamber. Right now it's an empty space with a pass through to the center chamber from the pipe I cut off. Any thoughts on benefit of using packing?

Gordo

[randywebb]

Interesting comparison...

Has anybody opened up a Monty muffler?

[Gordo2]

Welding it shut has been the toughest part yet, though nothing to complain about.

Took about 1 1/2 hours with a MIG welder hitting a small spot at a time. The 2 ply, thin SS shell is easy to burn through. Thanks to A Quiet Boom and Tim Hancock for the welding tips, I didn't have the guts to make my first try at TIG welding on my muffler.

I have some 3" SS exhaust tips inbound that should hide the ugly, will install them after I get a sound check. Don't want to waste the effort if it sounds like A$$.



Gordo

[Wil Ferch]

If ya used the same diameter "hole" on both sides....as I said many times before...be prepared for 70% (or so) of the sound to eminate from the right side... !!

Report back what you find...

Wil

[tdatk]

Originally posted by Gordo2
Another picture clearly showing the capped off "exhaust in" pipe. It seems this muffler would be very restrictive.



Gordo

Quick question.
Were the 3 baffles spot welded to the top cut away section? If so , how did you get it apart?
I'm going to cut my spare this winter as well.

[Gordo2]

For tdadk,

The baffles are not welded or attached to the shell in any way. Once you cut out the section it will come right off.

I had to bend the baffles down some to re-assemble. The casing/shell also has a tendency to spring out some, requiring a large C-clamp to hold it back together while you tack it in place.


For Will Firch,

It must be hard to tell from the pictures (take a good look, I didn't just add a second outlet). I welded both outlets together and have the exhaust passing to them toward the middle of the muffler's perforated pipes. No way I can get anything but even flow out of the pipes with the layout that I did. Quality of the sound though ... yet to be determined.

I may hold off on installing until I can get my cat bypass. I want the full effect rather than a part at a time.

Gordo

[Gordo2]

Update: I pulled my stock muffler off this afternoon (Bischoff stamped 7/82). It's different than the one I modified: the body of the '82 model has a smaller diameter than the '87.

As it turns out this is more than an interesting tid bit when it came to installing the modified '87 muffler; you got it... my muffler straps are too small.

I was itching to hear how it sounded (can you tell where this is headed ). Yup, nothin' a coat hanger couldn't fix. Hey, that's how they did it in Ohio where I grew up...

Overall, I like the sound:
- A nice rumble on idle, definitely louder than stock
- A deep roar under full throttle but not too excessive. Noticable.
- A little too loud for long 65 mph cruising in 4th gear (~3k RPM)
- 5th Gear brings cruising back down below 3k and into a smooth, relatively quiet rumbling range.
- Flow/sound from both outlets is very even.

I will wait to post new pic's until I get rid of the coat hanger and add the SS exhaust tips...

Gordo

[Gordo2]

Finally got around to installing the exhaust tips and wrapping up the mod. Here's my parting shots for the project:







Gordo

[tdatk]

Gordo,
Looks great! Any tips on the tips? Last shot you had the "ugly" on there and those ss tips came out perfect! Where did you get the tips also? As I said final shot is a great look.

[ThePointman]

WOW that looks SWEET!

[Gordo2]

Thanks, I like the idea of having a unique, one of a kind set up. The sound is awesome too.

I bought the tips online at Advance Auto (I think); $25 shipped for the pair. Had difficulty sizing correctly. The original outlet is somewhere around 2 1/4 OD, the p-side outlet I added was 2 1/2. Made installation a little more of a hassle. Also couldn't tell how long the tips were from the online info. I was a little surprised when they showed up being so long.

The tips are polished, heavy duty SS. Nice tips but wouldn't recommend them for Porsche application, due to the length issue. I had to cut the muffler pipes off near the muffler body to get the tips slipped on (otherwise the tips would have either angled completely 180 deg out or would have stuck out the rear too far) .

For reference
Total costs:
-Muffler off E-bay: $50 shipped
-Tips: $25
-Went to a Cat By-Pass in the process: $65 shipped (E-Bay)

Effort/tools:
-Cutting: Air Die Grinder w/cut off wheel, Dremel w/cut off wheel
-Welding: MIG welded everything shown

Gordo