993_Pilot

So I decided that I wanted some RSR's, but couldn't convince really justify the price to the "keeper of the checkbook". So, being a bit frugal, yet cautious, I purchased a set of mufflers off eBay for $50 to play with.

I liked the idea of keeping everything internal, but not really knowing what Robin does to convert to RSR's, I had to experiment. Here's what I did:

The first step was to clean up the exterior a bit and get rid of the surface rust and road grime. For this, I used a wire brush and a pot scrubbing pad that I swiped from the wife. They came out pretty good, but no where near as shiney as Robin’s look after he polishes them. This took me about an hour for both cans.

The second step was to cut open the cans. I don't have a plasma cutter, so a 4-1/2" angle grinder with a cut-off wheel would have to do. I put a mark about 3/4" from the back end of the cans as a guide and proceeded to cut. It worked pretty well and took about 3 minutes per can.

The third step was to open the cans up and remove the fiberglass packing. It took a bit of prying because the internals fit pretty tightly inside. (Note to self: This is where you should have put on a long sleeve shirt.) I then removed all of the fiberglass packing and took a wire brush to all the loose rusty scale that had built up inside. My arms itched for a week after this step!

For those who haven’t seen the insides of the muffler, it is basically a two stage affair. The inlet pipe of the muffler is basically a capped pipe with lots of little 1/8” diameter holes in it. About 70% of the exhaust gases must go though the small holes into the packing in what I’ll call the first stage. It then goes though a baffle with lots more of the little 1/8” holes that separates the stages. All this gas from the first stage then has to reverse course to get into the outlet portion of the muffler. About 20% of the inlet pipe vents directly into the second stage in the same manner as the first stage, but doesn’t have to go through any fiberglass packing. The last 10% goes through a small ~3/4" bypass similar to the LPMM which is contained within the first stage area. (Note: These numbers are are only a guestimate.)

Now for the fourth step… the modding. A one inch hole was cut the portion of the outlet tube within the first stage to allow first stage gasses to escape without passing through to diffuser that separates the stages. Two one inch hole were drilled in the diffuser itself, and about 8” was cut off of the outlet portion in the second stage to allow for a more direct path for the exhaust gasses. (See Pictures) The modding only took me about and hour and a half, but it took me a few days to decide on what to do. They were then taken to a guy who welds stainless (and does a much better job than me) to be TIG welded back together. The welding cost me $50.

My impression: While I don’t have any basis for comparison other than the un-modded stockers, They seem to be similar to what I have read about here on Rennlist about RSR’s or the LPMM. They are only bit louder from the drivers seat, but when you stand outside and behind the car, they take on a whole new note. It is now a much deeper rumble at idle and sounds a bit louder without being obnoxious when the rpm’s rise. It also seems to rev a bit more easily although that could be just the audio cues that are fooling me. There are no resonance issues at any rpm and it is hard to tell the difference from stock when cruising. Overall, I am happy for the time that I spent and the $100 it cost me, but I was hoping for a bit more from the driver’s perspective.

I was going to keep my takeoffs in stock trim, but this mod was tame enough that I might have to try this again. Next time I plan to enlarge the bypass portion from 3/4” to 1-1/2” , a la LPMM (The internal version). Stay tuned.

KBell

Great write up.
I admire your creativeness.

ARM993

Very cool Jeff. Would love to hear an audio clip of your results. Appreciate the write up and pics. Looks like a good afternoon project.

InTheAir

Cool.

Wilder

Nice. It'd be interesting for hear the difference between yours and the RSRs and LPMMs.

csertich

Thanks for posting. Pretty creative work.
chuck

allill

jeff,

next time i'm up there i'd like to hear these pipes.



-jf

99three

I'd also like to hear the difference your fab made. Nice work!

Toddimus

I like the creativity too! I didn't know that there was a factory bypass pipe inside the factory muffler. I love learning new things about these cars. Now you've given me one more option to ponder.

I'm new to the 993, going on 28 hours or so!

... aside...You know, you just can't wipe off that grin that's brought on by buying a 911. I know you folks reading this can relate to this!
... aside ...

I came from a line of older 911s, with the last one being a '90 C4. I had the "G-pipe" on it, which was "throatier" than the Bursch I had put on my previous '81 SC that was still pretty loud in its own right. How does your modification compare to those sounds?

My new one, a stock exhaust '97, NB is sure a whole lot quieter than these older ones!!

And in comparison to the other reasonably priced options, how does yours sound compared to the RSR or LPMM, which I haven't specifically heard yet? I probably have heard them before, but I didn't know what I was hearing.

Most of us don't live in Switzerland so we don't need to be as quiet, therefore we can take our engine trays off, and open up the pipes a bit. I'm just looking for the right first pass at an exhaust mod, and it looks like you have one that maintains that "stock" feeling. I like it.

Cheers

AM993

I think this is a characteristic of the mufflers of the optional Motorsound package.

Garth S

Even the stockers have an internal 1" bypass - while the motorsounds enlarge that to ~1 1/2" and utilize differing internals in a shorter 'can'. When I cut the outlet pipes of my stockers for the second gen LPMM:GS1 , I ran my index finger inside the opening like the average proctologist to confirm this .... but once was enough

AM993

Garth S, thanks for the clarification and the details about your finger's exploration

993_Pilot

allill
next time i'm up there i'd like to hear these pipes.

Send me a PM when you'll be in town. I would love to see that fat A$$'d cab of yours as well. My dad and brother both live in "The City" so I get there every few months. So, I may PM you too if thats o.k.

LJ in Van
Nice. It'd be interesting for hear the difference between yours and the RSRs and LPMMs.

Me too!

ARM993
Very cool Jeff. Would love to hear an audio clip of your results. Appreciate the write up and pics. Looks like a good afternoon project.

I haven't ever tried to capture an audio clip before. I'll give it a try when I get a chance. It may not happen for a while, because I am heading out of town for a week starting tommorrow.

allill

cool. just pm me jeff.

ANDREW_D.

Jeff, great work! Would it be possible to cut along the original seam to make the conversion rather than 1" down. This would preserve the original look. Andy.