Mad Muffler Mod

[NeedForSpeed]

We cut the top off of our muffler yesterday, a piece nearly three feet long and maybe six inches wide. About five spot welds down the length of the center had to be drilled, welds used to secure the muffler skin to separate walls and supports. The long cut was made just inside two other parallel rows of spot welds to avoid the extra trouble.

Inside, the muffler looked like a pipe organ, four or five pipes of varying lengths in parallel, each pipe slightly more than 1.5 inches id. Some pipes were short, one maybe six inches, another perhaps a foot long. A longer one below. These pipes are the only way for exhaust pressure to move between most of the walls, though some walls had a round opening or two. It seems one wall near the intake pipe was made of grate or large mesh.

There were two long pipes leading to the outlets. These pipes were solid for the first third, then perforated, six holes around, about 3/16" diameter. These holes were spaced every 2.5 inchs down the rest of the length. To exit, the exhaust pressure has to find the open pipe at the far end and travel the length of the muffler and out the tip, and/or be forced through the small holes into the pipe and out the tip. The long pipes make the exhaust path nearly three feet longer than it would appear by the looking at the exhaust tips. The holes may just dampen the sound by allowing the pressure pulses to travel in and out of the pipe.

This muffler is an impressive work of art. Nothing cheap about the design or build. I really hated to hack it up, but that's what extra parts are for! Only the long pipes going to the outlets were hacked, cutting out six inch sections between the walls. The exhaust pressure must still pass through two or three holes in the inner walls. The 'tuning' pipes designed to move exhaust pressure between two or three sections over were left alone.

A piece was fabricated and then welded back on top of the muffler. One of our friends is a master with metal, otherwise this probably would not have been attempted. Two to three hours for the project.

Once the trans is installed and everything is put back together, we'll let everyone know what we think of the sound. This is a California car and all three cats are intact. The resonator was replaced by straight pipe before the car found a home here.

The mad-mod should make more sound but probably not any difference in power. This is still not a flow through design and the stock exits are still in place. Essentially, the muffler was converted to a multi-chamber system from some variant of a non-flow-through perforated-tube system. So, whatever that means?!

[mikecg]

Did you think about makeing the short pipes between chambers a larger diameter? say something like 3 inch?

[SVXRide]

Good stuff! I had my machinist "pop open" a spare stock muffler I have a couple of weeks ago. We took pictures with his digital camera, but he's been too swamped with work since then to email them to me. We're actually planning on hooking a flow bench up to it to "play" a little. I've actually been considering opening up the end "ribs" and closing off the next "rib" in on each end to make larger end cavities. I've also thought about replacing the existing pipe with larger pipe, but I think you'd have to remove the entire "wrapper" from the muffler to be able to remove the existing pipes and weld in new ones.
-Bill

[Chiketkd]

Originally posted by SVXRide
Good stuff! I had my machinist "pop open" a spare stock muffler I have a couple of weeks ago. We took pictures with his digital camera, but he's been too swamped with work since then to email them to me. We're actually planning on hooking a flow bench up to it to "play" a little. I've actually been considering opening up the end "ribs" and closing off the next "rib" in on each end to make larger end cavities. I've also thought about replacing the existing pipe with larger pipe, but I think you'd have to remove the entire "wrapper" from the muffler to be able to remove the existing pipes and weld in new ones.
-Bill

Let me know how that project goes Bill and how much your machinist would charge for 'upgrading' the muffler. This could be an inexpensive way to free up more power...

-Chike

[wawazat??]

Nice job Ron!

Todd

[wawazat??]

Originally posted by Chiketkd
....how much your machinist would charge for 'upgrading' the muffler. This could be an inexpensive way to free up more power...

-Chike

You think a rocket ship scientist and a government machinist will be cheap

What are you smokin' Chike?



Todd

[NeedForSpeed]

Originally posted by Chiketkd

Let me know how that project goes Bill and how much your machinist would charge for 'upgrading' the muffler. This could be an inexpensive way to free up more power...

-Chike

Unless you use your own labor. You are talking several hours of time, some material and six linear feet of weld to put a top back on. That muffler wrap is spot welded everywhere, and then the ends are welded on. This would not seem an inexpensive mod unless someone could lend some time. The likely result is more sound with similar power.

Bill, I only took one picture, that with a disposable camera. Please post your digital pictures here, everyone will be amazed at what they see. Subaru spent alot of money developing and producing this piece to be quiet and to last.

What did you use to open it up? Did you open the top between the outside rows of spot welds like we did? Interesting comment on enlarging the outside cavities. Essentially, that is what we did by leaving the two inch section of pipe passing through the end chambers to the tips intact. The short end chambers can not exit exhaust. The far end can receive some exhaust pressure and redirect it through one of those tubes back toward the center of the muffler. Only the end farthest from the inlet has this redirection tube. The inlet pipe is cut at an angle, with the pulse directed to the near end. Wish we would have taken time for more pics, but we were hustling to get the rear diff gears swapped the same night.

Mike, enlarging pipes would be difficult and probably not helpful. The entire muffler would have to be disassembled to enlarge the holes in the walls/ribs for larger pipes. When you see pictures, it will be obvious. Believe me, if all the pieces were new and disassembled, if would be nearly impossible to weld this thing together. The short pipes are probably for sound tuning or pressure balancing, not to direct exhaust out of the muffler. Two of these short pipes of different length are in the top row, on longer pipe on the very bottom, and two long pipes to the tips.

[NeedForSpeed]

Originally posted by wawazat??
Nice job Ron!

Todd

Yes, it was one 'cuttin metal' night. First the muffler mod, second grinding the rear diff housing for clearance. I think we're ready to give birth to the transmission.

[Chiketkd]

Originally posted by wawazat??
You think a rocket ship scientist and a government machinist will be cheap

What are you smokin' Chike?

I guess I must have been sniffing my exhaust fumes for a bit too long this morning!

-Chike

[mbtoloczko]

I'm definitely interested in seeing the pictures.

[SVXRide]

Originally posted by NeedForSpeed


*snip

Bill, I only took one picture, that with a disposable camera. Please post your digital pictures here, everyone will be amazed at what they see. Subaru spent alot of money developing and producing this piece to be quiet and to last.

Will do! I'm actually going to take more pictures with my own digital. I was amazed at what went into the muffler design - you did a good job in describing it!

What did you use to open it up? Did you open the top between the outside rows of spot welds like we did?

A pneumatic circular cutter -- went through 1.5 blades. Just went deep enough to cut through the "skin" and then drilled out the spot welds.

Interesting comment on enlarging the outside cavities. Essentially, that is what we did by leaving the two inch section of pipe passing through the end chambers to the tips intact. The short end chambers can not exit exhaust. The far end can receive some exhaust pressure and redirect it through one of those tubes back toward the center of the muffler. Only the end farthest from the inlet has this redirection tube. The inlet pipe is cut at an angle, with the pulse directed to the near end. Wish we would have taken time for more pics, but we were hustling to get the rear diff gears swapped the same night.

Yeah, the first time I tried to follow the flow path it made my head hurt! What did you think about the two short pieces of tubing in the center? Given all the other flow paths, they struck me as balance/tuning pipes.
-Bill

*snip

[NeedForSpeed]

Bill,

Yes, those two unequal length pipes on top must be for balance or tuning because they aren't anywhere near the flow path or exit of the muffler. Did you notice the longer pipe in the bottom?

We used pneumatic circular disks, maybe four or five. The double layer side, where the skin wrapped over, really ate those disks.

I agree, it took a few minutes to figure out the flow path, if in fact there was one. My first impression was a pipe organ, lots of pipes, and walls to separate the muffler and locate those pipes. Though not designed for max power, this thing is a musical instrument!

Your pictures will be interesting to all, as this is really one amazing Subaru piece, unique to the SVX. I'm further impressed about Subaru's attention in designing and producing the SVX. This muffler may have had a different song in non-US cars;
fewer if any cats, lower gears, etc. After Subaru installed three cats for US cars, perhaps the unique song it was designed to sing was never heard.

What a show piece, to have one of these 'popped-top' mufflers hanging the shop wall. It is a work of art for sure. While we were working on the muffler at our friends rod restoration shop, a friend of his stopped by. He was a high-school shop teacher. He found the piece very interesting, and expressed interest in hearing the 'hacked' piece.

[Earthworm]

I guess no one has opened up a Stebro muffler yet?

[NeedForSpeed]

Originally posted by Earthworm
I guess no one has opened up a Stebro muffler yet?

is one big open chamber with compressed stainless steel mesh on inside. It has that big open chamber exotic sound, from what you all say. Wouldn't mind having one of 'em.

[mbtoloczko]

Originally posted by NeedForSpeed


is one big open chamber with compressed stainless steel mesh on inside. It has that big open chamber exotic sound, from what you all say. Wouldn't mind having one of 'em.

Yep, just a big can lined with ss packing and mesh covering the packing.