Leland Pate

Well, it seems many have voiced the need for a muffler that is a bit louder than RSR's but not to the extreme of the supercups or the like. I have formally volunteered to be the lab rat for this experiment. Tonight I cut open a muffler and am now contemplating how to go about modifying it. This is totally hit or miss, I know. I may end up worse off than before.

Here is a picture of a muffler cut open I swiped from a recent thread. I'd like some imput as to how best to go about modifying the pipe.
You can see the inlet and outlet and basically how the gases flow through the muffler. What you can't see in the photo is steel wool wrapped aroound the perferated pipe and matted against the perferated section of the inner wall. The rest of the void on the 'outside' of the wall was filled with fiberglass crap (I know because I'm itching from head to toe). The "wall" I'm refering to is the piece that seperates the two pipes on the back of the muffler as pictured. The space behind the wall was open.

So, after looking at what I got I have a few ideas. I have to be careful not to make a cut that is irreversable only to find out it sounds like crapola. I'm thinking a stepped approach might be best. For instance, I can re-wrap the perferated pipes with steel wool and loosely repack the can with new fiberglass and put it back together. I could then tack weld a coupple spots to hold everything together. Then I could temporarily use some metallic tape to cover the unwelded gap and go for a test drive. This way if it is obvious they are no good, I can easily grind the tack welds and try something else.

I've looked long and hard at the factory setup and am having a hard time figuring out how to rearrange or modify the pipes for a better sound. I want to start out modest and get more drastic as I try the easy things first.

So, now I open up the floor. If you were in my shoes, what would you try?

Feel free to draw arrows and circle bits on the photo to use as visual aids for your ideas.

Let 'em rip!

kkim

Since you know what the stock mufflers look like inside, I guess the next step is to find out what the supercups look like on the inside as well. That way you can target your modifications somewhere between the 2 design extremes.

Good luck on your project.

Terry Adams

Lee, not that I have a clue here, but you did prompt me to do some reading on muffler design

DJF1

My take on this is that you could make one piece solution as per pic attached.
Take a perforated pipe and make one piece. This way you can partially wrap it or leave it be, for noise adjustment. I'm not sure what part of it should be solid for gas acceleration and circulation, not an expert by any stretch, but I imagine the expense of doing this pipe would be minimal and if you have the time you can play with it and then dyno the sucker to see the results. You may even want to do this as a solid piece and play again with the noise.

Its an iteresting experiment for sure

Sorry my pic is very crude, paint made

PedroNole

Ok, here's my thoughts:

1) Steel wool and fiberglass were sound dampening materials to capture the sound that came through the holes in the one pipe. They probably played a role in reducing resonance too.

2) I think Danny is right about the one piece pipe. The trick then is probably the number/size of holes to drill in the pipe (much like the airbox modification except in reverse). The more holes, the more sound is released into the "baffle" of the muffler thus the less "direct" sound out of the tips.

3) The other thought I have is to move the "plate" that is between the pipe with holes and the pipe without holes. Something tells me that as you move this plate down, you will be capturing an increasing amount of sound going out the pipe without the holes, thus increasing exterior sound. However, I think you will need to keep the smaller pipe that runs between the two bigger pipes. This is probably a resonance tool and "release" for the air in the more open part of the muffler.

There will definitely be a fine line between nice sound and resonance as you either increase the holes in the pipe or move the plate down. I believe when you get it close, you will do the fine tuning with more steel wool.....

Mark in Baltimore

Supercups are essentially straight-through pipes and of a completely different design than stock, RSR's, Max-Flos, etc.The coveted early generations are nothing more than an open megaphone tube. The current gens are the same tube but have a perforated, smaller diameter pipe running inside the main body.

Ron

Leland,

Attached is picture I just took of one of the 1 7/8" I.D. 304 stainless steel U I had planned on puting in the muffler in the photo you posted. I had planned on drilling small holes in part of the U and re-packing the muffler with stainless steel wool.

cabfan1968

i am actually in the exhaust business and would also like to try some mods, however, the p-car mufflers are anything but conventional in design thus they are probably difficult to successfully modify one thing i am sure of is the importance of the insulation around the unit, it eliminates/reduces resonance in all applications, glenn

Leland Pate

Ok, so don't try to remove the filler- got it.

Glen, would you try to connect the inlet and outlet pipes in some manner? The perferated inlet pipe shown in the photo above is actually "capped" on the end. I've thought about cutting the cap off. Or perhaps drilling holes in the outlet pipe similar to the inlet holes and wrapping it in steel wool.

Or I can attempt, as suggested, to move the "wall" back and forth to see how that plays into the sound of the muffler.

Just from looking at the design, it is obvious this is not the most "free-flowing" unit ever designed.

Benton

I was going to start a business for Rennlist about 6 months ago, then I acquired my 928. I have experimented on two different sets and have found a great configuration that I could sell for cheaper than an RSR (not trying to steal Robin's business... these are louder and he stated he did the service for the community and not for profit), and I also already have four sets of mufflers to use as trade-ins. I was planning on starting my Rennlist sponsorship once I finish the 928 in about a month or so. I had already contacted Jenn about 6 months back and we had everything set up, but I haven't done anything since. I can take a sound clip if you guys would like; the mufflers sound great. They are fully TIG welded, back purged and weigh a ton less than the stock mufflers.

Edit: BTW, no resonance I've been running them on my car for about 5 months.

ventoGT

Red--could I hear your car sometime this weekend? I would definitely be interested....where do you work? I'm in Norcross but live near Buckhead....I'm interested in some new mufflers and would relish the opportunity.

Benton

Cole,
I'm kinda busy for the next few weeks, but what about the next mountain drive? Or you could come to my place (Gainesville) and check 'em out. I'm a student, but my current 30 hr/week job is to finish my 928. I'll also be out of town all next week (Bertil Roos racing school here I come!).

Alon

Have a look at what Fabspeed does when building their mufflers:

TroyN

Yes, please post a sound clip, or clips (from outside the car and inside), thanks!

cowtown

Leland, what a coincidence - I'm working on exactly the same project. Over the last week I have cut open and rewelded a pair of '95 Bischoffs. Against all the advice in this thread, my first step was removing the 2 pounds of packing material per muffler without changing anything else. I can replace it if it's way too resonant. I expect to try them out this weekend. So at least we should know just how boomy these things are without any fiberglass and steel wool in there.