Stock Exhaust Mod


Otters Pocket

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Yes the bit in red is the cat. I left it in too.

What you're suggesting will work, but too be honest is a lot of work trying to fit a new pipe for no point and I doubt you'd get much change in sound. If you want to do that I think the better way is to simply cut out the section you've put blue lines on and remove completely, then you have the same effect with less work. The gases go into that final chamber and then are free to exit anyway. This is basically what I've done above, but I've also cut out a large section of that final 'bulkhead' so that the gases not only have that final small pipe to go through, but a large area with far less resistance and straight to exit.
 

jeffrey1213

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Ok I see what you're saying. Yeah fitting new pipe would be too difficult. So then I'd also have to weld in a wall (marked in orange) to prevent the gasses from escaping through the other pipes (marked in red) out to the first chamber. I'd then drill/cut a hole where I've marked in yellow to let the exhaust straight out. Any flaws in this plan?

FullSizeRender.jpg

Alternatively to the orange wall, I could block off the two pipe openings individually. Whichever is easier, but if I put the wall, then I only have to cut open that top right corner of the exhaust.

Notes:
-the second blue line I drew closer to the bottom would actually be further up close to the orange wall so that I could open up a smaller section of the exhaust.
-where I marked in yellow, I wouldn't actually be cutting from that side, I'd be cutting from the right-most chamber
 
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Otters Pocket

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Again I'd say you're at risk of overcomplicating things.

If you cut the pipe out (in blue) and open up the yellow part, then you've got the effect you want. The gases can potentially go through the pipes marked in red, but they then have nowhere to go, so form a sort of natural barrier anyway if you see what I mean. The gases will want to go the easiest route which is straight out the exit once they've pressurised that back section.

If you want to go for something a bit more full blown, look at ToastedBlue's post above - you could even do that off the cat if you wanted and pop in a larger exit pipe.
 

Timbo108

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Hi if someone wouldn't mind answering, I have a couple questions. The part I circled in red I'm assuming is the cat, can someone confirm or correct me? I plan on making cuts where you see the blue lines (removing most of the exit pipe), then adding pipe where you see the green lines (connecting the short pipe directly to the exit pipe). My thought process is that I want the exhaust to go through the cat (to keep my pants from having that cat-less stench lol) straight into the mid-section and let the exhaust muffle a little bit in there and then head in the short pipe & straight out the back. Any tips or other comments on this would be appreciated! Thanks!
View attachment 5982
The blue lines are exactly where I cut, leaving the rest alone. I thought of cutting a 2 1/2" hole in the bulkhead that separates the center from the rear chamber but wanted to keep the sound level reasonable. orked well for me.
 

jeffrey1213

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Reason I wanted to do it like that is cause I figured I should do as much as I can to open it up because it can't get that loud. Like aftermarket systems which are pretty much all straight pipes with no cats. Even the way I blueprinted it, the exhaust still gets muffled a little bit in the mid and right section before heading out. And that's after going through a cat.
 

Otters Pocket

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Reason I wanted to do it like that is cause I figured I should do as much as I can to open it up because it can't get that loud.
You have the restriction of the final exit pipe diameter, so most of what you mentioned wont really make any difference anyway.

To properly open it up you have to follow ToastedBlue's method which is more akin to a proper aftermarket system. As Timbo108 says, just cutting the exit pipe (blue lines) out will be enough to get the 'improvement'. Cutting a much larger hole in the bulkhead which I did was just a 'while I'm in there I might as well' approach. Going to the trouble of welding additional walls etc, I'd definitely rather just go for the straight through pipe instead for the effort involved.

No big deal though, any of it will give you a much improved sound, I guess the best way is to simply get it open and have a go and report back. If it works really well would be good to document for the rest of us :)
 

jeffrey1213

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So if anyone's interested or looking into doing what I did on my 2018 XSR900 (same exhaust as FZ-09 / MT-09), here it is with pictures and links to all the materials. It's a good amount of work, but I wanted to have the racing sound & (most of the) performance while keeping the cat so that I (especially my pants) didn't smell like a burnt piece of garbage after riding. The only aftermarket exhaust options for this bike with a cat are $1k+ when they're even available so I consider the work put into this well worth it. The end result came out perfect and exactly how I wanted it to be and I have never even cut a piece of wood in my life, so if you're a beginner, have no fear.

1. I made a cut (shown in red), cutting the whole back off the exhaust off and discarding of it. I used an angle grinder to cut the perimeter and a reciprocating saw to cut the pipes inside to get it apart.

2. I got a 3" ID (inner diameter) to 2" ID exhaust pipe reducer (shown in blue). I had to cut each side to shorten the length of it so that I would have enough room for the rest of the parts without hitting the rear tire (tight clearance). I cut 2cm off of each side but it will vary depending on where exactly you cut the exhaust. Just go for it then figure it out. Make the 2" side of the reducer sit flush with where you cut the exhaust.

3. I got a 12"x12" piece of sheet metal and traced the 2" side of the pipe reducer onto it, then cut the hole with a 2 1/8" (the outer diameter of a 2" ID hole) hole dozer on a drill. Then I stuck the reducer (blue) onto the exhaust and put the sheet metal (also red) over it and traced where to cut the sheet metal to a size to cover up the back of the exhaust. After test fitting everything on the bike, I welded the reducer onto the cat, then I sanded and sprayed it with the heat resistant spray paint which is an exact match to the factory coating (you can skip the spray for this part because it is stainless steel). Then I sanded and sprayed the inside of the sheet metal (side that is going to be closed up inside the exhaust) and welded it on. Make sure you do this because it will rust VERY quickly.

4. Then put the exhaust back on the bike and put the elbow (shown in green) and slip on (shown in yellow) on and and put a couple of welds between the slip on and elbow to hold it in place. Then take it off and fully weld around it. Then put it back on and hold it in place so that it clears everything and weld the rest. Then sand and spray the exposed sheet metal and exiting pipe.

Parts:
2" ID to 3" ID Exhaust Pipe Reducer Connector Adapter 304 Stainless Steel
Rust-Oleum, Flat Black 248903 Automotive 12-Ounce High Heat 2000 Degree Spray Paint
Stainless 2" 45° Mandrel Bend Elbow - 1.5D/3" CLR Loose Radius - 16GA/.065" Wall - No Leg - SS304
M-D Building Products 56038 1-Feet by 1-Feet 16 ga Weldable Steel Sheet
38-51MM Exhaust Muffler Silencer Slip On Dirt Street Bike Motorcycle Scooter

Tools:
BLACK+DECKER Angle Grinder Tool, 4-1/2-Inch, 6.5-Amp (BDEG400)
DEWALT Cutting Wheel, All Purpose, 4-1/2-Inch, 5-Pack (DW8424B5)
BLACK+DECKER 20V MAX Reciprocating Saw, Tool Only (BDCR20B)
*Remember to get one with battery if you don't already have one from another Black+Decker tool
Freud DS0908CF Steel Demon Carbide-Tipped Reciprocating Blades for Thick Metal Cutting, 9"
2-1/8 in. Hole Dozer Bi-Metal Hole Saw with 3/8 in. Arbor & Pilot Bit

IMG_8659.jpeg
IMG_7907.jpegIMG_7910.jpegFullSizeRender.jpeg
IMG_8655.jpeg
 
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Otters Pocket

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A lot of work for a similar result, but I guess if you like the end result that's the main thing.

A question though - you say you want the 'racing sound' but use a restriction down to 2" after the cat. IMO going to all that work, you could have just stuck with 3" pipe all the way in a similar approach to ToastedBlue above (but leaving the cat in place). Also, why have you got that silencer on at all? Am I missing something, the stock bike doesn't need a silencer and that will just restrict the sound further?

I'm thinking with a silencer on you could have simply cut away the entire box leaving just the cat going into the pipe you welded on and maybe a bracket, would have made the job a lot easier and saved weight, as all those chambers are now just dead weight and not doing anything.

Any video on the sound difference? Would be good to hear for people wanting to choose an approach.
 

Timbo108

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After my tinkering with and modifying the stock exhaust, I'm happier after spending the $445 for a full Delkevik exhaust, Looks and sounds quite nice.I added a 6" section of ceramic fiber matting around the internal baffle to lower the volume a tad, hit a sweet spot for me. It also retained the stck o2 sensor. I'll post a photo if someone will expain how to do it. sku COM01B9
 
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jeffrey1213

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@Otters Pocket So I used the 2" reducer in order to fit the silencer. The reason I got the silencer is because without it, it sounds like a fart can IMO. The silencer doesn't really have any restriction, it more just acts like a resonator and gets rid of the unwanted sounds. It also does come with a baffle so there is some adjustability which may be a bonus to some. I also wanted it to have some sort of visible tail pipe for aesthetic purposes. And to answer your other question yeah there is some dead weight, but I did the least amount of cutting required in order to expose the cat and connect my pipes. In the end, I'm very happy with the sound. It's as loud as I'm willing to tolerate lol but doesn't sound straight piped obviously. I will take a video at some point to post.
 

Otters Pocket

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No worries, just interested really, I don't find the stock exhaust sound bad, especially with the mod, but surprised me to see a silencer fitted after the box. I personally would have removed the box completely in that case (tool the cat out and welded it on) and then simply had the straight through with the silencer on the end, which is basically what an aftermarket pipe is.

Anyway, the main thing is you like the effect, so it's all good :)
 

fidobite

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Has anyone compared dyno output before and after one of these mods?? A lot of engineering goes into these exhaust systems by the manufacturers to balance noise/performance/emissions. Usually messing with the exhaust without other considerations leads to a loss of performance, though the sound may be worth it if it's not too extreme a loss.
BTW-just bought a new '19 and it is sweeeet!!
 

Otters Pocket

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Has anyone compared dyno output before and after one of these mods?? A lot of engineering goes into these exhaust systems by the manufacturers to balance noise/performance/emissions.
For a NA engine, the important design is the scavenging, which is done before the cat in the header pipes using the cross sections. These create low pressure in the adjacent pipes to help 'draw' the exhaust gases exit from pistons about to open the exhaust valve. Once through the cat, which is the main restriction, the baffles are simply to slow down the gas velocity to reduce noise on exit, so this is the part that can be managed fairly easily without risk to the fueling.

I haven't had any dyno work, but I can tell from the 'bum dyno' it's not affected, but also because I have a flashed ECU with TFecu lambda sensor so I can monitor and adjust the fueling maps. It will show me if the fueling is out anywhere (which it isn't) but also adjust if needed to bring the fueling back.

The bike in stock form will also do this to a certain extent through it's own lamba sensor.

I do however agree that if you were to massively change both the exhaust and airbox e.g. straight-through pipe and K&N fitler etc, then a remap would be best to ensure the fueling is increased to match the increased air flow. For these small changes to the baffling though I wouldn't worry about it.
 

jeffrey1213

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No worries, just interested really, I don't find the stock exhaust sound bad, especially with the mod, but surprised me to see a silencer fitted after the box. I personally would have removed the box completely in that case (tool the cat out and welded it on) and then simply had the straight through with the silencer on the end, which is basically what an aftermarket pipe is.

Anyway, the main thing is you like the effect, so it's all good :)
Yeah that's what I was going to do at first but decided the amount of cutting and grinding to make the look clean wouldn't be worth the benefit for me. But you could definitely do it and shed a few pounds off of the weight.
 

Den

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Have seen a couple of posts on this, but none recently and not ones that have been what I'm after, so I'm going to mod a stock can myself and see what the result is like.

So I saw this mod which looks really good at turning the stock exhaust into pretty much a straight through pipe, but for me it's a bit too on the raucous side and I want a more subtle tone change

So the stock exhaust looks like this inside:



The gas flow is sent into the middle chamber, fills the area, passes into the right chamber, fills and then through a pipe underneath the short upper pipe that's visible into the left chamber and then finally into the long pipe all the way to the outlet.



Not great artistry but gives you the idea.

So in the video, he guts the lot and makes a straight through pipe. I've also seen a video where a guy cuts the right most outlet pipe, but the effect is minimal, since the short pipe is still quite a restriction and leaving the other pipes open still allows a lot of the gases to be sent the long way round.

My thinking is it will be better to block that short pipe in the right panel, then cut the section of outlet pipe, so the gases only travel into that middle section before filling the chamber and then going straight out. This isn't far off being straight through, but the fact the gas fills the central chamber allows some slowing of the gasses speed and disturbs the flow enough to reduce volume to (hopefully) a nice level.



This also has the benefit of only needing that small middle section to be opened up and a couple of cuts with a reciprocating saw to knock out the central piece. Block the small pipe off and also the section now open to the left chamber and the flow is straight through to the outlet.

Found a stock Tracer exhaust on ebay for a nice cheap price so I'll not be hacking up my original (if it's a tad too loud can still use that for MOT's etc) and will get the angle grinder and welder out when it arrives and let you know how it goes. As I say, hopefully it will give a much nicer deeper tone but not be anti-social or draw attention from the police etc.

I did this mod last week. Removed the system myself and cut the bum out of the muffler with a grinder and cutting disk. That was a mission. Yamaha sure didn't want anything coming loose. I didn't have anything to cut the pipes so took it to a muffler guy to cut them out and weld it back together.Didn't touch the Cat. $200 NZ and it was done. Easy to reinstall. Haven't had a chance to get out on the road but at rest it sounds a lot deeper without it being too loud. Using my phone decibel app only went up 2 decibels. Can't wait to hear it under load.
 

Den

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Have seen a couple of posts on this, but none recently and not ones that have been what I'm after, so I'm going to mod a stock can myself and see what the result is like.

So I saw this mod which looks really good at turning the stock exhaust into pretty much a straight through pipe, but for me it's a bit too on the raucous side and I want a more subtle tone change

So the stock exhaust looks like this inside:



The gas flow is sent into the middle chamber, fills the area, passes into the right chamber, fills and then through a pipe underneath the short upper pipe that's visible into the left chamber and then finally into the long pipe all the way to the outlet.



Not great artistry but gives you the idea.

So in the video, he guts the lot and makes a straight through pipe. I've also seen a video where a guy cuts the right most outlet pipe, but the effect is minimal, since the short pipe is still quite a restriction and leaving the other pipes open still allows a lot of the gases to be sent the long way round.

My thinking is it will be better to block that short pipe in the right panel, then cut the section of outlet pipe, so the gases only travel into that middle section before filling the chamber and then going straight out. This isn't far off being straight through, but the fact the gas fills the central chamber allows some slowing of the gasses speed and disturbs the flow enough to reduce volume to (hopefully) a nice level.



This also has the benefit of only needing that small middle section to be opened up and a couple of cuts with a reciprocating saw to knock out the central piece. Block the small pipe off and also the section now open to the left chamber and the flow is straight through to the outlet.

Found a stock Tracer exhaust on ebay for a nice cheap price so I'll not be hacking up my original (if it's a tad too loud can still use that for MOT's etc) and will get the angle grinder and welder out when it arrives and let you know how it goes. As I say, hopefully it will give a much nicer deeper tone but not be anti-social or draw attention from the police etc.

This month (August 2021) I did my Tracer muffler same as this post suggested. Quite a fair bit of cutting involved to get the bottom off but got there in the end. Took it to a muffler company to cut the pipes and weld everything back together. Refitted and it definitely sounds better although not as loud as I expected.
On the stand it has only increased the decibel reading by 3 decibels but sounded deeper.
Took it for a squirt and has a deeper note under load now. Thinking that if I had removed the Cat there would be a much louder sound but all in all fairly happy now.
 

Mikrad

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It's a good mod, I did the same to my 2015 MT09 just this weekend after reading this post.
I managed to pick up a second exhaust for $10! so no reason not to experiment!

Definitely a bit of fun with the sabre saw hacking away the internal pipe. but after a bit of work with the grinder and flap disc managed to tidy it up.
A mate at work welded it up great and put it back on yesterday.

Definitely a nicer deeper note and all I think you would want to not be both satisfying and not annoying.

My "bum dyno" detects a drop in instant response at the low end, but the mid to top appear to be "freer" and revs out nicer and more freely.
As I commute, and lots of stop-start, that drop in response bugs me, feels like a drop in torque that I really liked with the stock exhaust.

Do you think this is a fuelling issue (now leaner?) that could be rectified to give the response/kick back? Cheers guys.

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