Muffler - Where's the Can Opener?

With the help of a welder/muffler man, I've decided to convert a dual inlet/single outlet muffler to a dual out. I've located a stock, pre 74 muffler in good shape. I am planning to use the outlet on my existing rusty muffler as the right side outlet on the newer one.
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For those of you who have made this conversion, where do actually open the muffler to modify the guts to ensure back pressure on both sides is equal? On the seams or just cut it open the entire length? Any trick to tacking on the second outlet?
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Thanks in advance
Chuck
83SC with SSIs

Iv'e seen it cot in the same place as the existing outlet no metion of back pressure I could be wrong

Sorry about the typo I mean the other end gets cut and welded up.

There are a couple of ways to do this.
- The easy way: drill a 1/2 inch hole where you are placing the second outlet. Install the muffler and sound test. Keep drilling the hole larger until you get the required level of sound. Install the new tail pipe over the hole. Note - the noise level goes up real fast as the hole gets bigger, there is no baffling material at the right end.
- The hard way: Take an air chisle and pry open the muffler case. Re arange the innards to suite your taste. Dirty job.
- The sport muffler way: Run two pipes straight out the back. Weld up the original tail pipe. After you cut the holes for the twin pipes take a large flat blade screwdriver and knock out the metal webbing that separates the upper and lower chambers. This results in an indirect flow through = loud.
The first two options allow you to choose the sound level you prefer. The sport muffler option really doesn't.

Chuck,

Before you do the final welding of the outlets, you might want to contact SPD - Specialty Products Design in Rancho Cordova, CA 888-778-3312 ... they have 304 stainless tubing mandrel bends in large sizes such as 3" and I believe just a couple of 90 degree bends could be cut/trimmed into oulets which could be nickel-silver brazed to your banana muffler to 'advertise' your SSIs to the world!

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Warren Hall
1973 911S Targa

To add to Warrens reply, when I changed my exhaust to B&B headers I bought an ss muffler can from Fabiani. Its loud!!, but that's beside the point. The install required the cutting and welding of 2 180 mandrel bent pieces of 3" ID ss tube to connect the headers to the muffler and then to make the 2 outlets. Any competent muffler shop can handle this stuff easily. The fit and appearance are superior to off the shelf stuff.

For those with access to 'Up-Fixen" vol iv there is a sketch of the mods to make a hot dog into a twin out sport muffler. Early straight out the back style.

Thanks all for the replies - -
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Warren, I'll give SPD a call on Monday - thanks for the tip.
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Rarly - two questions for you - - First, you say the right side of the stock muffler has little or no sound baffling material - - But is the right side a common area, internally, for the both the right and left inlets? In other words, if you cut a hole in the right side, is equal back-pressure on both banks of the engine preserved - - - Or is this a non-issue?
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Second question, re Hard way option, the air chisel - - where on the bananna do you make the cuts? Just guessing off the top of my head, I would say the bottom or the rear of the muffler.
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Of course, this may be covered in Up-Fixen - thanks Bill. (Nice pics, too) I'll have a look. As great as this BBS is, it's too easy to pose the question here rather than doing a bit of research on my own.
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Chuck

I looked into doing this before deciding to go with the dansk dual-outlet.

At each end of the muffler there is an expansion chamber, so you are not going to run into any problems when you cut the hole.
I have seen some pics where people have welded on the stainless outlets, they look nice. Start with a small hole, though, I have a feeling it gets really loud, pretty fast!

BTW, I have a dual inlet, single outlet OEM muffler that I got from Tom Sharpes. It came off his 73 S that has only 50K orig. miles. The muffler is in PERFECT condition, no rust and no debris inside when shaken. Since I have decided not to use it, If anyone is interested, drop me an e-mail at nickshu@yahoo.com

Nick.

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Nick Shumaker
1982 911SC Coupe

Chuck,
The answer to your first question is no, opening up the right side alone will not equal the pressure to each side. It will decrease the backperssure for the entire system. When I was playing around with this "quick and easy" method I used a 1/2 inch hole. The majority of the exhaust still exited from the left or stock side. The sound, backpressure, and performance all improved.
As for opening up the muffler, you follow the seams. There are what seems like hundreds of spot welds to chisle. The original outlet may need to be cut off. This mod is not an easy thing to do. The muffler is packed tight with sound deadening material and a lot of baffles and chambers that are welded into place. Get a schematic before going in. If I had a scanner I would post it. Sorry. When I did this mod I moved both tail pipe positions tward the bottom of the muffler on each end. This allowed more room for the polished SS tail pipes and NO MODIFICATIONS to the bumper or valance. You can also do this mod on the quick and easy version muffler as well.




[This message has been edited by RarlyL8 (edited 02-17-2001).]