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Discussion Starter · #1 ·
CAM00947.jpg CAM00948.jpg CAM00949.jpg CAM00950.jpg CAM00954.jpg
Some of you may be interested in this, sadly without taking off the top like I have, gutting then making some new internals there is naff all you can do with the standard muffler. The big restriction is the 1.5" link pipe just after the cat, there are gaps around the baffles which allows some gas flow, but in general that little 1.5" pipe flows 95% off everything after the cat, by the way the latter is huge. No joy to be had here without massive rework.
 

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Discussion Starter · #3 ·
So that's what the inside of da scrotum looks like.
Yep it does look like a ball sack, I have a bit of an idea for the muffler which may be a goer, keep you all posted
 

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Very interesting.

1) Open the "wall" right after the cat, it would flow exhaust directly into the 3rd chamber.
2) Open the 3rd chamber with a larger final pipe, as some have done already. (But with limited result, as we can see now why.)

The rest is not worth chasing. the bent pipe that results in the final exit pipe, starting in chamber one, has a necked down inlet with a venturi.
It has the 'db' killer just on exit of the "scrotum."

A long air hammer cutting tip might make this mod possible. Cut off the ENTIRE final exhaust tip leaving about a 3" hole. (Measure the bulged area, and cut accordingly.)

then clip off the pipe from chamber one so it's sticking OUT of the bulge you just cut. (There is a reason for it to be longer, it's going to be used to help accelerate gas scavange from the 3rd chamber.)

Now, between the pipe and the new cut opening, make your best guess where the cat is on the other side of the wall, and cut a large nearly closed C with the open part of the C facing the longer exit pipe.

BEND the C in towards the CAT. Pushing the lip of the C cut flap into, and then past the CAT if you can. My thought is the cut flap part of the wall from your C is now going to help smooth gas flow out of the cat, from chamber two into chamber 3.

If I was going to open it up, I'd cut a pipe here, cut a nice round hole in the 3rd chamber wall, and NEARLY butt the pipe up against the cat exit, flairing/venturi the area nearly butted up against the cat, while leaving the exit flat, and only go about 2 or 3 inches past the wall like the stock cross pipes, as this flows best in this design.

The result of a mod like this would be possibly VERY LOUD.
The C door? not as loud, but it's possible.

Part is going to depend on how big a C cut can be made, if it's exactly in line with gas exiting the cat etc. Any misaligned openings will disrupt flow, causing it find the path of least resistance, and that's going to flow things out the stock pipes in many cases.

Option B would involve cutting holes in the wall where the cat exits. Put as many holes into that wall as you can drill. It's going to be messy flow wise, but it's going to flow more for sure. Think shower head of exhaust gas into the 3rd chamber, and it's going to swirl around before it can be expelled either by other gas flow, or pressure. (Flow good, pressure bad.)

This is where a longer stock exit pipe up the center of the new larger final tip will help scavenge gas from chamber 3. The same idea is how media blasters work, only you are sucking out exhaust gas, not aluminum oxide or glass beads.
 

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Looking at the inside of that muffler, it is amazing, that it sounds, and works, as well as it does.
No doubt, the size of the muffler itself, provides enough volume "size wise" to let it flow free enough to make the power it does.

Has anyone run a stock FZ09, against one with a slip-on or full system, for the fun on comparison?

Riders of equal weight, would help the match-up. What I am getting at, is to see where the torque "Sweet spot" gets moved around to, with an unrestricted exhaust.
 

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I have read,somewhere, that the reason the exhaust path loops back is to get the optimum turned length.If a can is connected right at the end of the collector the tuned length is wrong.
I believe some of the better after market manufacturers have a loop to lengthen the exhaust path.
 

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Discussion Starter · #7 ·
I have read,somewhere, that the reason the exhaust path loops back is to get the optimum turned length.If a can is connected right at the end of the collector the tuned length is wrong.
I believe some of the better after market manufacturers have a loop to lengthen the exhaust path.
Which is why the Akro ti is a bit of a strange pipe, mimicking the standard ball bag to a point, wonder if it has an internal mid pipe? the mid/secondary pipe helps with scavenging and is a tuned length, much like the headers themselves, which explains why the carbon Akra pipe is the one to have performance wise, it has a nice long midpipe. there is no real mid pipe in the standard muffler, just a great big cat chamber that's about 8 inches long about 8 inches back from the probe port, then its just a series if baffles and small pipes which flow the gasses.
 

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Don't leave out the sound waves the stock design is using to help move gas too. Chamber designs like this can do amazing things if you designed them with a computer, and some testing time involved.

It's why I'm not doing much with this design will net results across the board. All the aftermarket pipes give up low end for peak power. (Not that this bike needs much more low end in reality.)

I really just want a slightly LOUDER exhaust. I don't think loud pipes save lives, but I do like a bike I can enjoy listening to while I ride it, and this one is wind noise and tires... With some exhaust sound track laid in down there somewhere under the engine noise, and timing chain.

If a few hours of my time cutting off the stock exit pipe, grafting on a 3" ID version that's "ovalized" at the tip to fit the stock cover with some work opening it up to fit a 3" slash cut pipe... And simple air hammer cut work to the baffle/wall between the cat and the 3rd chamber? That's worth the time, and should be louder.

Will it make more power? I doubt it, but I don't much care. LOL
Will it be loud enough? I suppose we will only find out when it's done that way.
 

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There are some interesting details to the stock design, like flared pipe to minimize inlet pressure drop at the 1.5" short piece. It looks well-thought out, but also compromised. It makes more power below 3500rpm than any after-market system, but falls short as the revs rise, probably because of the flow restriction caused by the honey-comb cat. It would be nice if there were an easy way to just remove the honey-comb and leave the rest alone. I did this on a Tiger 1050 by working an impact chisel on the cat material through the inlet. You would only need to clear a 2" path to get more flow and sound. With all that muffler volume, it should be nice, deep and throaty.
 

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There are some interesting details to the stock design, like flared pipe to minimize inlet pressure drop at the 1.5" short piece. It looks well-thought out, but also compromised. It makes more power below 3500rpm than any after-market system, but falls short as the revs rise, probably because of the flow restriction caused by the honey-comb cat. It would be nice if there were an easy way to just remove the honey-comb and leave the rest alone. I did this on a Tiger 1050 by working an impact chisel on the cat material through the inlet. You would only need to clear a 2" path to get more flow and sound. With all that muffler volume, it should be nice, deep and throaty.
If you want a bit more sound, it's easy to remove the "decibel killer" in the tip & replace it with a larger outlet. Much easier than hacking the whole muffler apart to get at the catalytic converter, and is cleaner air really such a bad thing? Just my opinion of course.
 

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i would REALLY like it if someone could post a video of what the bike sounds like coming straight out of the cat. This way we could figure out if you can rip out all the internals and leave the cat with a decent sounding bike.
 

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Well, there is only the thin wall between the cat exit, and the tail pipe chamber.

But, you have to cut the stock tail pipe off, put a bigger one in place, and first cut open the chamber wall, exposing the cat exit to the last chamber.

Might be TOO loud however.
 

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I'd be willing to bet that cutting out the cat and replacing it with a pipe of similar O.D. would do the trick. Leaving all the other internals and the exhaust pathway exactly the same would likely keep it pretty quiet still. Anyone try this?
 

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I'd be willing to bet that cutting out the cat and replacing it with a pipe of similar O.D. would do the trick. Leaving all the other internals and the exhaust pathway exactly the same would likely keep it pretty quiet still. Anyone try this?
Nope....no matter what you do...the stock exhaust still has the exit the muffler through a One and half inch pipe.

Old school rules are ...one and a half exit....too quiet...one a five eights exit is near perfect without being too loud....and one a three quarters exit....is deafening.
 

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I love when these old threads pop back up.. means members are using the search tools.

Hacking the stock exhaust could be a fun thing for someone who likes getting their hands dirty. But the only real benefit to this modification is increase in sound.

Any HP increase would be nice, but in the end will never compare to the Power / weight ratio gains on an aftermarket system.
 
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