Gut Job for Sound Performance...
 

Alright boys and girls,

Since so many of you are fascinated with "Sound Performance" over actual car performance, I'd figure I'd write this up as it is relevant to that topic.

I know there are at least a couple guys running gutted mufflers but afaik, it's never really been documented before. According to them, this is suppose to produce a nice sound with no drone. I usually don't write these kinds of pieces as many things have already been documented and I hate redundancy.

Why gutted mufflers over a PSE or Fister style mod you ask? Some reasons would be a little weight savings, factory type look(Cali peeps and inspection), possible tuneable sound to one's preference(I'll get to that later below).

I haven't really had any time to tinker since having kids and taking on a big house remodel/renovation but I had to take a break from both which allowed me to finally start my gut process that I had planned to do for quite some time now. WARNING: This is a teaser and who knows when I'll be actually be able to complete it and install it. So proceed at your own risk if you don't want possible blue balls.

https://lh3.googleusercontent.com/-I...7_15_20_35.jpg

I found this to be the best way to cut and gut with the least amount of cutting and rewelding. Best to cut case with a cutoff tool and use a Reciprocating saw with a long metal blade to cut through the internal tubes. Using these two tools will allow you to gut each muffler in about 15-20min each.

https://lh3.googleusercontent.com/-1...7_15_20_36.jpg

Basically, you can see that there is a primary muffler/silencer which has a tightly packed steel wool wrapped within it's own steel cylinder. This then goes into a larger muffler chamber that is perforated at the bottom which is lined with finer fiberglass on the other side of the perforation at the bottom which then is fed into the top chamber that also has perforations to diffuse the sound further before the exit tube picks up the air from the middle chamber.
https://lh3.googleusercontent.com/-s...7_15_20_36.jpg

Based on this, you can see why the "PSE" style mod wouldn't be as effective/loud as the air is still passing through both internal mufflers before coupling to the exiting pipe. This basically is foregoing the sound reduction in the top and final chamber only.
https://lh3.googleusercontent.com/-n...7_15_20_36.jpg

Also note the double wall construction of the muffler casing. This is one of the reasons why the mufflers are heavier than they need to be but provides better structural support and corrosion penetration.

Ok, once you cut out part of the muffler case, you basically cut all the tubes in the top and middle chambers. Once you do that, you should be able to wiggle out each internal baffle one by one as the baffles themselves are held in by tension(grooves on the case) and not welded or even tack welded in any way.
https://lh3.googleusercontent.com/-5...7_15_20_36.jpg

Also important to note that some older mufflers that have been severely corroded and make noise usually stems from the center tube as that is the one that is tack welded and with the least support since it isn't supported by both internal baffles. So for those wanting to fix a rattling muffler may only need to cut into the center section where the center pipe is located.

Now I mentioned going this route would let you tune or customize how loud you want yours and I haven't done all the configurations to know exactly how loud each combo would yield but going by common sense, here's my take on it:

For the least amount of sound increase it would make sense to cut the first(a) pipe only so that it is basically bypassing the top and final chamber of sound reduction. Personally I don't think this would be worth it as sound increase maybe very negligible and not really noticeable.

The second stage of sound increase would entail cutting the first(a) pipe and a section of the last(c) pipe's casing so some sound bleeds out into the middle chamber while the rest goes through the second silencer

The third stage of sound increase would entail cutting the first and the very end of the last pipe so that is gets silenced by the first silencer only and bypassing the larger second silencer. It would be interesting to see the harmonics or timbre variation between leaving the second larger silencer in place or removing it to see what it does to the timbre of the exhaust note. Theoretically leaving the second silencer in should yield a higher pitch sound.

Lastly, for full sound increase, removing all the internals would yield the most volume.

Additional pics:
Flow Diagram along with typical sound increasing mods
https://lh3.googleusercontent.com/-T...42/diagram.jpg

Shows top and bottom baffles with perforations
https://lh3.googleusercontent.com/-i...7_15_20_36.jpg

Another view with my trusty $9.99 Tool Shop cutoff tool that's saved me many times and going strong after 5 years.
https://lh3.googleusercontent.com/-A...7_15_20_36.jpg

Shouldn't be too bad to weld back together however, I ran out of Argon and never refilled it. I may take this to local muffler shop next time I have some time or get my tank refilled. I don't know when that will be though.
https://lh3.googleusercontent.com/-7...7_15_20_36.jpg


That's it for now. Don't hold your breath for an update.

This is without opening mine up, but I think I'm going to get some flex hose from some shop and make a tube out of that which fits into the current muffler opening, poke holes in it, and wrap with steel wool.

Or, make a pipe going straight to the secondary chamber from the intake and call it a day.

Alp you beat me to this. I have been wanting to do this for quite a while now. I had found a video on YouTube with a guy that did both mods (gundo hack and gutted mufflers) on 2 different sets of cans. Both sounded similiar in the video so i asked him which was louder. He said the gundo hack was a tiny bit louder so will hold off from gutting until you give us a little more input. I will try to find those clips in a few days. Now off to Vegas.

This is a cool writeup. Thanks Alp. Makes me want to pick up an extra set of takeoff mufflers and mod them so I can keep my originals just-in-case. Looking forward to seeing/hearing what comes of this.

I believe that the small chambers on the sides are there for higher frequency noise reduction, and the open chamber primarily for lower frequencies. So the PSE mod, for example, which skips one of the small chambers, should let some higher frequencies through. This is what would likely give you more of the nice "rip" sound at the higher end of the rev range.

Very cool! Thanks for posting all this!
Exhaust sound is a really important part of the driving experience for me so I'm really diggin' this stuff.
My car had PSE originally but then the cats went and I got a cat delete with 3rd muffler. Then a muffler went and was replaced with non-PSE. The other muffler is now on the way out so when it comes time to replace it this mod could be just the thing for me (and maybe get me kicked out of the neighborhood).

The different chambers don't have too much to do with frequency IMO. Look closely at the pipe setup and you will understand.

Also the real PSE mufflers are setup a bit different internally. I was referring to the PSE "style" mod.

Nice.. I ran like gutted mufflers on my 996 and loved them. My friend runs them on his now. Nice sound, major weight lose, and some performance increases.

You were partly to blame for me vandalizing this set.:) Without your feedback, I'm not sure if I would've done it.

Wife: why the hell are you destroying your good mufflers?

Me: because I belong to RL.

Wife: oh I understand.

I will look into this more, but when I had glass packs put on the Jeep the shop made a comment that they take out the high end and leave the low rumble that everyone loves.

So, I'd almost say (just off the top of my head, I'll do more research later when I cut mine apart) that the main packing you outlined does a bit to the high end as well as the end, where maybe the lows would be taken out by the baffles.

Just my guess anyway.

Wow, very cool thanks for posting. I've been brainstorming how to cut open mine to do some surgery, this really helps.

I have stainless rods for an AC buzzbox not sure if I could weld the case back together with those, my MIG is set up for mild steel :( and I expect a garden variety muffler shop welds would rust out in a couple years?

Cool... Did you put them on your car yet?? I am looking forward to your response..

Not yet

I guess my response could be somewhat confusing but yes the packing material would certainly alter the tone and what you mean by "high end" could also be described as raspiness which a silencer/glass pack/resonator/extra muffler can reduce.

In this case however, the primary function of the two silencers are to reduce sound levels I feel first and foremost.

PMKazz would be the best person currently to weigh in on whether his gutted mufflers sound raspy or high pitched at all compared to the non-modified OEM cans.

I'm subscribing.

Me too!