Inside the FJ muffler

[rodan]

Well, today I swapped out the mufflers. And the first attempt is a bust. Those of you who have been following for a while will remember that I sourced an FZ-09 exhaust for this project, making some assumptions that it would be identical to the FJ-09 piece, with the exception of the outlet and outlet garnish. Well, that assumption was wrong. The brackets on top of the muffler, while identical on both mufflers, are around 1/2" further to the rear on the FJ version. So it wouldn't bolt up to the chassis.
 
Here's the two for comparison:
 

 
I also goofed on the outlet, and it's not positioned correctly. Next step is to move the brackets rearward, fix the outlet, and try again...
 
Oh, FYI, the centerstand needs to come off to remove the stock muffler. I thought I could get away with not taking it off, but learned differently.

[b12ty]

Ack, that sucks, who would have known by looking at it that they were 1/2" different. I didn't need to remove my center stand, BUT... I have the low profile oil drain plug installed. Makes all the difference.
 
Carry on, good luck.
 
Ty
 
 

[rodan]

Yup, the low profile drain plug would have made the difference on removal with the centerstand. Good to know!

[traceroz]

You can leave the centrestand on when you take off the exhaust. Leave the RHS muffler bolt loosely attached, and 1 exhaust flange bolt loosely attached. Put bike on sidestand, remove last bolts, remove exhaust. Drops straight off.

[markus]

You did great work, guys, all of you!
Tomorrow is the day, I get an extra stock exhaust and this one will be cut...looking forward to that! I cannot weld, so I´ll have to give it to a welder. Don´t know when that will happen...I hope VERY soon!
 
Thank you all and best regards from Germany
 
Markus
 
 
 

[skyrebel88]

You guys have made great steps forward. I think the akra Ti exhaust has the same flow path as the stock exhaust minus the cat. Maybe you could test that design next with larger chamber connection pipes as well?

[ausmt07]

I can't wait to see the results on this; I'm wanting to do something very similar on my 07!

[adjuster]

Well, dang it all. I have a GPR exhaust for the FZ09 sitting in my kitchen, but need to put it on the FJ09 now that I have this bike not the FJ....
 
And you guys have done what I was thinking about over on the FZ09 side of things.. A hole to let some exhaust out post cat, and into the final chamber, no S pipe etc.
 
But, I like the gutted version too, but would consider this: Using the complete volume of the stock "Scrotum" housing, you could run three perforated pipes. One would go straight out of the header/collector pipe, where the stock Cat is located, and then go back to the rear. A middle pipe goes in the middle.
The "exit" pipe is also perforated, and goes from the front to the rear, like the stock S' pipe, exits out at the tip. (And could be used stock this way if you wanted, just cut off the pipe where it meets the perforated pipe.)
 
Bell end the right sides for flow. Build simple "walls" for the front and rear out of sheet metal, wrap the perforated pipes in the packing: 1. Stainless, wrapped with stainless wire to secure it. Followed by fiberglass, also wrapped by wire to retain it tight, and then stuff the rest full of stainless scrub brushes and whatever fiberglass/stainless packing material you have left.
 
The tight wraps on the three pipes in the middle will make the difference on how long they work, and how effective they are at cutting down the noise level, while still flowing like there is nothing there. With this design, it's open on the ends, like the stock design. This allows sound to bounce around and cancel some waves out too. (Not that I'm going to even attempt the math and precision needed to make a harmonic design work, it's clear Yamaha did some fancy design work on the stock muffler, it's to complex for no other reason than to cancel out waves and freq's they did not want while perhaps even boosting low end power.)
 
Using the "Bell" ends on the flow into pipe sides will give free gains in power. And having it all 2" from the stock colletor to the tip should flow plenty for top end power on this bike, while the large distance of the flow should also help maintain good low end power/tourqe delivery.
 
Short of gutting the entire pipe, here is my take on the very easy way to mod the stock design.
 
1: I see there is a large hole in the case where the S pipe exits. This sharp edge can't help flow, creates turbulence etc. (Remove as much of this with a pineapple carbide cutter as possible after the "bulge" is cut open.)
2: The "X" over the cat is made of thin metal.
3: No need to add a nice fancy pipe to the wall there, but to just let more of the sound, and exhaust skip the entire trip around the inside, and escape out a short cut to the exhaust tip.
4: Why limit to just a 2" tail pipe, and oval shape? I'm thinking there is a radical tri-oval in there folks, just trim the stock bezel, and use a grinder to open it up just right, and it's going to be nice megaphone indeed.
 
So, using a 3" or perhaps even larger ID stainless pipe, I'm thinking of cutting off the tip at the bulge and leaving as much of the "S" pipe as possible. Cut around the bulge at the case, and then chop the pipe off just inside of the weld where the "S" pipe is attached to the exhaust tip.. The tip will come off, leaving part of the "S" pipe sticking out, with a larger 3" or so hole in the bulge area that you just cut open.
Trim the useless sharp edge of the case out of the way around the bulge weld attachment point. Leaving the "S" pipe still hanging there in space, attached to the rear wall.
 
Now use a long air hammer with a cutting tip, and following the "X" marks the spot, use it to cut a nice "X" in the panel that the CAT dumps against.
 
Now with some skill and luck, bend those "flaps" made by the "X" cut towards the back of the muffler, opening it up just enough to get the sound and flow you are looking for.  (Have just the right custom bent screw drivers and pry bars for this I think...)
 
No need to cut the entire case open. Put it on the bike, and take it for a ride, make some adjustments for noise and flow levels.
Measure and tack your "Tri-Oval" tip in place, ride some more, and if you have to, remove the tip, open the flaps or close them to get the noise/flow levels you want, and then when good, remove the muffler, and finish weld the new 3" ID pipe onto the bulge/case as needed, fabricate the cover mounts etc.
For the final fitment, you use a short section of metal, and secure the exit point of the "S" pipe in the middle of the new larger exhaust tip pipe. This should actually create a scavenging effect on the "S" pipe, as any exhaust going out either pipe is going to help draw out exhaust from the other depending on the pressure in either.  If you don't want to, or if it's a PITA, just bend the "S" pipe over till it just touches the new "Tri-Oval" and drill a nice hole there. Position, clamp, and spot weld the "S" pipe into place by welding it through the hole, fill the hole, and file it smooth, and it's secure, and you did not have to try and weld inside the pipe.. No fun indeed, much more fun to weld on the outside.. LOL
 
Now give it a nice coating of black paint, but leave the tip and cover stock, just hide the scrotum with flat black paint, and leave the headers nice looking too if you like.
 
Might just be time to break out the MIG and tools, and have some fun. BTW, all you guys who had trouble filling the cut gaps, it's really easy to use welding rod, or any other material you might have to help fill the gap. Just take welding rod, tack it in the middle of the gap, laying down into the gap, and tacking it about every 4 inches or so, and use the heat of the tack to help bend it into the curves, a few taps of a hammer help here, but with a long welding rod, you have enough control of the metal to just "push it" into the gap, tack and push some more, easy peasy. Weld up between every other 4" tack, and you control the heat, don't risk warping the entire project, and it's going to be WAY less of a swear fest for blowing through the thin material, and it's dirty sound packing on the back side that's causing all sorts of havoc with your weld too. If you have a really wide gap, just run two passes of welding rod when you tack. The extra filler material will make the weld nice too, as it's generally nice and clean.
 
So, there is one more question that nobody has done yet, and I'm itching to try:
 
Why no mounts on the stock muffler for a nice skid plate?
 
I'm thinking a nice stainless one, not too thick with some formed/rolled ridges for strength, attached to the stock muffler with 4 nuts welded to the case? It can extend forward over the stock oil pan, and with a low profile plug, and the "crack ridge point" removed with a file, you just leave a nice hole for the drain plug, so you don't have to remove the skid plate... Curve the front edge slightly, perhaps weld some thicker solid bar stock in a "U" shape that runs around the front, and then back to the rear where it's bolted to the pan mounts to keep the edge from curling up under impact....
 
There you go, modded muffler, and kickass skid plate in one smooth move.

[adjuster]

The Akra has a chamber that's dead ended next to a pipe that feeds to the rear chamber and the exit.
With the dB killer removed, the Akra is basically an open pipe.
With the dB killer in place, it forces the exhaust to flow out the smaller pipes, and that allows it time to resonate more into the "Dead end" chamber that's next to the straight pipe.
Think of it like a this: IJ, With the I being the dead pipe. The J being the straight pipe, with the header at the top of the J, and the comma is the tip. With the tip in place, the sound can't just go out, it has to go around out the smaller 3 pipes, and that allows it to bounce up and into the I that runs fore and aft of the chamber.
If you look into the open Akra tip, you can see the cut outs that allow it to flow straight out when the "tip" is removed, but how it forces the exhaust to use the smaller 3 pipes when it's in place.

[adjuster]

Well, today I swapped out the mufflers. And the first attempt is a BLAST! (Fixed it for you. 
Love this photo! I cracked up and had to exclaim: "It's alive! ALIVE!" in my best Young Dr. Frankenstine impression.. Dude, that's only two welded on bolts and two smiles away from being the Frankenstine brothers photo of the year!
 

 

 

[b12ty]

Well, dang it all. I have a GPR exhaust for the FZ09 sitting in my kitchen, but need to put it on the FJ09 now that I have this bike not the FJ.... 
And you guys have done what I was thinking about over on the FZ09 side of things.. A hole to let some exhaust out post cat, and into the final chamber, no S pipe etc.
 
But, I like the gutted version too, but would consider this: Using the complete volume of the stock "Scrotum" housing, you could run three perforated pipes. One would go straight out of the header/collector pipe, where the stock Cat is located, and then go back to the rear. A middle pipe goes in the middle.
The "exit" pipe is also perforated, and goes from the front to the rear, like the stock S' pipe, exits out at the tip. (And could be used stock this way if you wanted, just cut off the pipe where it meets the perforated pipe.)
 
Bell end the right sides for flow. Build simple "walls" for the front and rear out of sheet metal, wrap the perforated pipes in the packing: 1. Stainless, wrapped with stainless wire to secure it. Followed by fiberglass, also wrapped by wire to retain it tight, and then stuff the rest full of stainless scrub brushes and whatever fiberglass/stainless packing material you have left.
 
The tight wraps on the three pipes in the middle will make the difference on how long they work, and how effective they are at cutting down the noise level, while still flowing like there is nothing there. With this design, it's open on the ends, like the stock design. This allows sound to bounce around and cancel some waves out too. (Not that I'm going to even attempt the math and precision needed to make a harmonic design work, it's clear Yamaha did some fancy design work on the stock muffler, it's to complex for no other reason than to cancel out waves and freq's they did not want while perhaps even boosting low end power.)
 
Using the "Bell" ends on the flow into pipe sides will give free gains in power. And having it all 2" from the stock colletor to the tip should flow plenty for top end power on this bike, while the large distance of the flow should also help maintain good low end power/tourqe delivery.
 
Short of gutting the entire pipe, here is my take on the very easy way to mod the stock design.
 
1: I see there is a large hole in the case where the S pipe exits. This sharp edge can't help flow, creates turbulence etc. (Remove as much of this with a pineapple carbide cutter as possible after the "bulge" is cut open.)
2: The "X" over the cat is made of thin metal.
3: No need to add a nice fancy pipe to the wall there, but to just let more of the sound, and exhaust skip the entire trip around the inside, and escape out a short cut to the exhaust tip.
4: Why limit to just a 2" tail pipe, and oval shape? I'm thinking there is a radical tri-oval in there folks, just trim the stock bezel, and use a grinder to open it up just right, and it's going to be nice megaphone indeed.
 
So, using a 3" or perhaps even larger ID stainless pipe, I'm thinking of cutting off the tip at the bulge and leaving as much of the "S" pipe as possible. Cut around the bulge at the case, and then chop the pipe off just inside of the weld where the "S" pipe is attached to the exhaust tip.. The tip will come off, leaving part of the "S" pipe sticking out, with a larger 3" or so hole in the bulge area that you just cut open.
Trim the useless sharp edge of the case out of the way around the bulge weld attachment point. Leaving the "S" pipe still hanging there in space, attached to the rear wall.
 
Now use a long air hammer with a cutting tip, and following the "X" marks the spot, use it to cut a nice "X" in the panel that the CAT dumps against.
 
Now with some skill and luck, bend those "flaps" made by the "X" cut towards the back of the muffler, opening it up just enough to get the sound and flow you are looking for.  (Have just the right custom bent screw drivers and pry bars for this I think...)
 
No need to cut the entire case open. Put it on the bike, and take it for a ride, make some adjustments for noise and flow levels.
Measure and tack your "Tri-Oval" tip in place, ride some more, and if you have to, remove the tip, open the flaps or close them to get the noise/flow levels you want, and then when good, remove the muffler, and finish weld the new 3" ID pipe onto the bulge/case as needed, fabricate the cover mounts etc.
For the final fitment, you use a short section of metal, and secure the exit point of the "S" pipe in the middle of the new larger exhaust tip pipe. This should actually create a scavenging effect on the "S" pipe, as any exhaust going out either pipe is going to help draw out exhaust from the other depending on the pressure in either.  If you don't want to, or if it's a PITA, just bend the "S" pipe over till it just touches the new "Tri-Oval" and drill a nice hole there. Position, clamp, and spot weld the "S" pipe into place by welding it through the hole, fill the hole, and file it smooth, and it's secure, and you did not have to try and weld inside the pipe.. No fun indeed, much more fun to weld on the outside.. LOL
 
Now give it a nice coating of black paint, but leave the tip and cover stock, just hide the scrotum with flat black paint, and leave the headers nice looking too if you like.
 
Might just be time to break out the MIG and tools, and have some fun. BTW, all you guys who had trouble filling the cut gaps, it's really easy to use welding rod, or any other material you might have to help fill the gap. Just take welding rod, tack it in the middle of the gap, laying down into the gap, and tacking it about every 4 inches or so, and use the heat of the tack to help bend it into the curves, a few taps of a hammer help here, but with a long welding rod, you have enough control of the metal to just "push it" into the gap, tack and push some more, easy peasy. Weld up between every other 4" tack, and you control the heat, don't risk warping the entire project, and it's going to be WAY less of a swear fest for blowing through the thin material, and it's dirty sound packing on the back side that's causing all sorts of havoc with your weld too. If you have a really wide gap, just run two passes of welding rod when you tack. The extra filler material will make the weld nice too, as it's generally nice and clean.
 
So, there is one more question that nobody has done yet, and I'm itching to try:
 
Why no mounts on the stock muffler for a nice skid plate?
 
I'm thinking a nice stainless one, not too thick with some formed/rolled ridges for strength, attached to the stock muffler with 4 nuts welded to the case? It can extend forward over the stock oil pan, and with a low profile plug, and the "crack ridge point" removed with a file, you just leave a nice hole for the drain plug, so you don't have to remove the skid plate... Curve the front edge slightly, perhaps weld some thicker solid bar stock in a "U" shape that runs around the front, and then back to the rear where it's bolted to the pan mounts to keep the edge from curling up under impact....
 
There you go, modded muffler, and kickass skid plate in one smooth move.

Wow, we have an expert! Looking forward to your results!
 
Ty
 

[rodan]

This has gone waay on the back burner for me, so it would be nice to see someone make some progress...

[papac2000]

What was wrong with what we did, Ty? Still lovin' mine, how about you?

[b12ty]

What was wrong with what we did, Ty? Still lovin' mine, how about you?

 
Loving mine also, ended up taking my homemade baffle out and leaving it that way for now. Nice to have the choice, and fun to experiment!
 
BTW: I've now done 3 FJ-09's now, everyone happy with the sound and notice the power increase too! I believe leaving the cat in mellows the sound, and leaves just enough back pressure to not kill the bottom end, as your dyno results showed.
 
Cheers, Ty
 

[adjuster]

Looking at the GPR, and what GPR did to it's header and muffler to move it out next to the swing arm, and not keep it under the bike like the stock location is interesting.
 
The center stand rubber bump stop and mount is possibly in the way of a muffler, but can be modded to clear I suppose.
 
I do really think that a skid plate using the stock muffler is a good idea, and one that with some careful design, could be done for a stock muffler, just by using self tapping screws to attach the skid plate to the stock muffler. (Drill pilot holes, and let the self tapping bolts enlarge them while they thread the holes, and attach the skid plate. Not the most elegant fix, but it's practical, and let's face it, the underside of the bike is not looked at much, and a skid plate would be a seller for both the FZ and FJ versions of this bike worldwide.)