Inside the FJ muffler

[papac2000]

Here's the link.
 
http://fj-09.org/post/2937

[rodan]

That's very similar to what I'm thinking of... hopefully a little nicer fab work, though.  It also looks like he used a typical, cheap packing material.  I'm guessing it will be unreasonably loud in less than a year.  I don't want to have to cut the thing open to repack it, so I'm thinking of a stainless steel packing material, similar to what Staintune does.
 
For posterity, here's the video:
 
 

 
And this one shows what he did inside...
 

 

[b12ty]

Yesterday I received my FZ-09 exhaust, purchased as a new take-off from eBay.  I wanted to experiment on a spare exhaust, just in case this all goes horribly wrong, or I just get tired of being noisy and want to go back to stock.  
First thing, I weighed it on my super-accurate scientifically calibrated bathroom scale:  17.5lbs
 
Then I started comparing it with the stock FJ-09 exhaust, looking for any differences.
 

 
The first thing to note is that the cosmetic outlet cover is longer on the FZ version, and has an additional bracket forward.  This would interfere with the centerstand on the FJ.
 

 
However, the FJ cosmetic cover fits on the FZ version, with one bracket being slightly in the way.
 

 
Here is the stock FJ with the cover removed showing the two brackets that hold the cover.
 

 
And here are the different brackets on the FZ version that will need to be removed.
 

 
The exhaust itself, and the top bracket which mounts to the frame, appear identical.
 

 
So, it appears that the FZ version can easily be used on the FJ by cutting off the two unused brackets, and fabricating a bracket for the FJ cosmetic cover, which is already required when increasing the size of the outlet tubing.  Easy peasy!  So, now we know we have a cheap source for stock exhausts!
 
Next step is to cut the muffler/cat section open and examine the guts.  My intention is to do much more extensive surgery than the pioneers here, and perhaps construct a straight through exhaust, with no cat, similar to an aftermarket setup, but concealed in the stock box.  Stay tuned....

 
Ty
 

[rodan]

Started the gutsectomy on the stock FZ muffler yesterday.  Here's a couple of pics showing the exhaust flow, which we had a good idea of from previous posts in this thread.
 
This one shows the front opened up revealing the cat, which I don't think we've seen before:
 

 
From the back:
 

 
As you can see, gases flow out of the cat into a flat plate, find their way to a very small tube into the rear chamber, then to another small tube back into the front chamber, then into a tube that takes them in a circuitous route to the outlet.
 
The plan is to remove most of the guts, and replace them with a perforated tube that routes the exhaust straight through, like most aftermarket mufflers, and fill the rest with packing material.
 

 
I've ordered most of the stuff I need to get it done, but it's going to take a week or so to get it all in.  In the meantime, I'll be breaking out the plasma cutter to go to town removing the guts.
 

[b12ty]

Looking forward to the results!
 
Are you gonna keep the stock exhaust tip, or go bigger? I went with the 2" outlet, but i'm not sure it's needed.
 
When I did Lewis's muffler, we kept the stock tip, nice sound, and power increase! And not as "boomy" at idle. In fact i'm experimenting with a mild DB killer, basically going back to stock outlet diameter. Not quieter, just softer at idle. Took a ride this morning, and that triple sounds really sweet. Man, I love this mod!
 
Just removing the S pipe and adding second outlet from the Cat chamber is all that is really needed imo. Just FYI to any who are contemplating doing this mod.
 
I'm also very curious to see how rodan's approach turns out!
 
Ty
 
 
 

[ULEWZ]

Looking forward to the results!  
Are you gonna keep the stock exhaust tip, or go bigger? I went with the 2" outlet, but i'm not sure it's needed.
 
When I did Lewis's muffler, we kept the stock tip, nice sound, and power increase! And not as "boomy" at idle. In fact i'm experimenting with a mild DB killer, basically going back to stock outlet diameter. Not quieter, just softer at idle. Took a ride this morning, and that triple sounds really sweet. Man, I love this mod!
 
Just removing the S pipe and adding second outlet from the Cat chamber is all that is really needed imo. Just FYI to any who are contemplating doing this mod.
 
I'm also very curious to see how rodan's approach turns out!
 
Ty
 
 

If you do the BTE ride tomorrow, we can compare sounds. If the weather holds that is. We melt in rain here in So. Cal.  

[papac2000]

"Just removing the S pipe and adding second outlet from the Cat chamber is all that is really needed imo."
 
From a sound standpoint and return for effort invested, I will agree with you Ty. BUT...
I think that the stock outlet diameter will cost hp. Not that that was ever the point to this excercise, but still bears consideration. Here's my logic:
The collector of the header is decent in size, as is the cat itself. Where the bottleneck occurs is when it gets choked down to 1 3/8" coming into the rear chamber. Once that is cured, the outlet is the "new" bottleneck. I agree that 2 holes at 1 3/8" through the baffle AND the 2" outlet are overkill, both from a sound and flow standpoint. So...either one 2" pipe through the baffle in place of the smaller original one along with the 2" outlet OR, a small 1" hole beside the original one (like mine) with the 2" outlet would be the ultimate recipe to make best power without being too loud in my opinion. As far as power goes; my prediction, after running hundreds of bikes on the dyno over the years, is the mod with both the extra hole in the baffle AND the 2" outlet will see gains right to the limiter. (Already documented) while the stock outlet version will gain in the midrange and sign off around 9500 as the stock system does. It may make 1 or 2 peak hp gain.
Thoughts?

[b12ty]

Well, as Lewis noted in one of his posts, he definitely noted a power increase with stock tip. As do I still, even with stock diameter insert. Front wheel still gets awful light where it didn't stock! Top end? Who knows without a dyno. I'm making my insert removable of course... so I can have it both ways.
 
I believe the gains are made mostly with the second hole in the cat chamber. ( along with removing the s pipe, of course ) It's designed to have the output of the cat slammed into the rear chamber wall, then have to go sideways and back to get to the rear chamber. As you noted, your dynoed gains came from what you thought was reduced back pressure from the cat chamber. The second hole is right inline with the cat.
 
Fun stuff!
 
Ty
 
 

[rodan]

My intent is to run 2" all the way through, so the diameter remains the same from the collector through the outlet.  This should be equivalent to running any of the aftermarket systems, as that is essentially what they are doing.  It probably won't be as light, but it will be a little more stealthy (looks, anyway).  I'm hoping it won't be too loud....  I can always build a restrictor, if necessary.  Hopefully the extra volume of the muffler will absorb more sound than the smaller aftermarket setups and keep things reasonable.
 

[b12ty]

Perforated tube going to run the whole length of the muffler, I assume? Then pack with fiberglass/steel wool? Ya, that does sound like a typical aftermarket pipe. Basically what I have on my other bike, and that sounds perfect.
 

 
Looking forward to pics and sound clips.
 
Ty
 

[rodan]

So, I've received all of my exhaust materials...
 

 
2" perforated tubing, 2" 'U' bend, fiberglass packing, and two types of stainless wool packing. I went a little overboard on the packing stuff (I have more than is in the photo), but I wanted flexibility in how I design the packing, and it was relatively cheap. I want it to last as long as possible, so I'll start with the coarse stainless wool around the pipe, then the fine stainless wool, and use the fiberglass to line the muffler chamber. Since the fiberglass is most susceptible to breaking down from the sound waves, that should be the most durable setup, while absorbing the most sound. Then again, I could be out to lunch! We'll see...
 
Hopefully I'll get some time early next week to work on it.
 

[rodan]

Finally got back to the FJ muffler, after getting several other priority projects out of the way...
 
Attacked it with a combination of cutoff tools and plasma cutter and removed all this:
 

 
Which leaves it looking like this:
 

 
Here's the new path mocked up:
 


 
Still have a bit of fitting to do, then need to start welding things back together... stay tuned...
 

[papifun]

Rodan.. Now u got me curious
 

[papac2000]

Well, as Lewis noted in one of his posts, he definitely noted a power increase with stock tip. As do I still, even with stock diameter insert. Front wheel still gets awful light where it didn't stock! Top end? Who knows without a dyno. I'm making my insert removable of course... so I can have it both ways. 
I believe the gains are made mostly with the second hole in the cat chamber. ( along with removing the s pipe, of course ) It's designed to have the output of the cat slammed into the rear chamber wall, then have to go sideways and back to get to the rear chamber. As you noted, your dynoed gains came from what you thought was reduced back pressure from the cat chamber. The second hole is right inline with the cat.
 
Fun stuff!
 
Ty
 

 
I had my bike back on the dyno as I was curious to see the fueling without a remap. Other times I had not bothered, but I just wanted to check so I know where things are. With my modded exhaust the fueling is steady at 12.9-13.0 across the board from 4-11000. I put this in this thread because I noticed something when making a backup run without the probe stuffed in the outlet. It made 3hp less with the "wand" in the outlet than with it out. I think this confirms the bigger outlet is worth hp....but again, that was never the point of all of this in the beginning. Just passing along results.

[b12ty]

Well, as Lewis noted in one of his posts, he definitely noted a power increase with stock tip. As do I still, even with stock diameter insert. Front wheel still gets awful light where it didn't stock! Top end? Who knows without a dyno. I'm making my insert removable of course... so I can have it both ways. 
I believe the gains are made mostly with the second hole in the cat chamber. ( along with removing the s pipe, of course ) It's designed to have the output of the cat slammed into the rear chamber wall, then have to go sideways and back to get to the rear chamber. As you noted, your dynoed gains came from what you thought was reduced back pressure from the cat chamber. The second hole is right inline with the cat.
 
Fun stuff!
 
Ty
 

I had my bike back on the dyno as I was curious to see the fueling without a remap. Other times I had not bothered, but I just wanted to check so I know where things are. With my modded exhaust the fueling is steady at 12.9-13.0 across the board from 4-11000. I put this in this thread because I noticed something when making a backup run without the probe stuffed in the outlet. It made 3hp less with the "wand" in the outlet than with it out. I think this confirms the bigger outlet is worth hp....but again, that was never the point of all of this in the beginning. Just passing along results.

Hey, good to know our fueling is not messed up by doing this mod!
 
Just out of curiosity, how big was the probe you stuck in your outlet? Enough to account for the difference of a 1.5" to 2" tip ya think?
 
I did go ahead and make a DB killer of sorts. A tapered I.D. reducer bushing that fits inside the 2" tip. I then welded the original tip to that, and secured it inside the 2" pipe with a couple of screws that I threaded into the bushing. Softens the sound at idle, and doesn't sound so "boomy" inside my helmet. I'll have to get a pic of it sometime. Sounds great on the throttle still, and easily removable if I want.
 
 
rodan, any plans to dyno your bike after you finish the exhaust?
 
Ty