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I have a new theory:
Based on @GoFaster Hindle header for the YZF-R3 specs:
Hindle exhaust system on my bike uses header pipes with a nominal diameter of 38.1mm
By using the Hindle header with a nominal diameter of 38.1mm, could that header be used in conjunction with a very long silencer/muffler, like the Delkelvic 18" Stainless Steel Oval Muffler (457mm length, 51mm pipe diameter) and an extra long baffle, like the Paughco Universal Exhaust Baffle for 2" Pipe (13-1/2" Long) 77A (342mm length, 51mm diameter) to produce the low-end to mid-range torque I'm really after?

Oh wait... Because the Delkelvic slip-on is 51mm and this baffle is also 51mm (diameter), well, I'd have to find a smaller diameter baffle to fit inside the Delkelvic silencer/muffler.

But that makes me wonder... What diameter baffle produces more low-end and mid-range torque?

I'm also wondering: does the quality of muffler packing and baffle wrap material affect the rates of exhaust flow restriction?


Obviously I'm at the point where searching the internet might not provide good results... The point where I will have to start buying parts and developing a solution through my own R&D (research & development).
The other part of this theory is to utilize (as @R3Wheelchair suggested), the expansion valve R25 exhaust pipe in conjunction with the idea of a long muffler.


Here's another interesting expansion valve idea to fabricate into the mid-pipe (of perhaps the Hindle system):
 

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...Since I had the OEM muffler removed, I ground off the rivets that held in the cap in place and popped off the end cap to take a look inside...
Was there any muffler packing in the OEM muffler and if so, what was its condition (and please tell us your mileage)?
 

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Was there any muffler packing in the OEM muffler and if so, what was its condition (and please tell us your mileage)?
My moto is a 2017 Yamaha MT-03. Same motor as the R3 to my knowledge. 40,000km on the odometer.

I guess I should have taken some fotos but did not. I had to grind off the S/S rivets to pop the end cap. The silver end cap is about the size of a coffee mug.

Once the end cap is removed you will see a solid steel plate across the muffler body. The only opening in this steel plate a 1" steel tube. This the 1" tube that you see that exits the end cap. The solid steel plate is the location where I drilled the six 8mm holes in a circular pattern around the 1" tube. The 1" steel tube is about 6" long. At the other end of the tube behind the steel plate you can see another flat steel plate. There appears to be about a 1" gap between the end of the tube internal in the muffler and this steel plate. There was no visible packing anywhere that I could see. The muffler design appears to be similar to my Honda dirt bike mufflers, older style XR and CRF air cooled bikes.. I suspect if you cut the Yamaha muffler in length you would find a series of vanes and bends that creates a U-shaped path for the exhaust gas flow. It is not a gatling style muffler with a straight path for the exhaust gases.

If I can figure out how to post a sound video I will do that. I have not test ridden the moto on the road but plan to do so today.
 

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Unfortunately Vertical Scope doesn't give us easy ways give emojis as reactions.

I think the community would agree, you deserve this 🏆, @kiko.
Copy emojis from emojipedia.com

Once I get into modifying the the exhaust (all this talk has made me wanna keep my R3), I will be interested in fuel maps for the hack job you described.
Maybe I could even run the stock system with the RCMini5 and AF1 to see if there are any performance gains. There are just so many different things I want to test.
Not to mention [is a phrase] the suggestions @Dreadwil, @R3Wheelchair, and @GoFaster recommends or advises.
This opens up a whole new adventure with the bike.

I directed @Primal to this thread...I wonder what he might put together (I'm interested in the results), too.
 

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Well I went for a test ride about 120 miles. Below 7000 rpms the motor felt a little soft with less engine braking. I had become accustomed to engine braking in the curves to modulate my speeds so it was a pucker A** in the first curve when I entered hot and the Yamaha did not slow down when I reduced throttle because engine braking was less than before. That took some adjustment on my part so I decided to increase engine rpms by about 1000 rpms at each shift point to compensate for the small loss of engine braking. After I moved up the shift points, engine braking returned as I was accustomed to. I found myself in 4th gear more often than before when I would have been in 5th gear.

I do not know how much the ECU can tweak A/F mixture but on the way back the motor felt stronger as if the ECU had reset itself. That could be complete BS and just a seat of the pants observation.

I might plug two of the six 8mm ports in the muffler and just experiment a little bit, but overall I am happy with what I have now. Another idea I have is to pack some coarse steel wool (pot scrubber material) into the end cap as an experiment. It would have to be packed in loose. I like the Delkevic 200mm exhaust a lot but I would think I would lose engine braking with that design and I suspect it is a real headache trying to tune that back in with a baffle.
 

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So by "unplugging" the stock silencer/muffler...
I'm going to take a guess and say you have lost low-end torque and lost top-end horsepower. If this is the case, then your top speed will be negatively affected (instead of 110mph, it might be more like 105mph hitting a rev limiter).

You've essentially confirmed the facts about losing the stock restrictions, thereby reducing the "back pressure" or "negative pressure" effect. This causes the R3 engine to run out of power, because the exhaust is running wide and open. Without other modifications (airbox mods, ecu tuning) you may not recover the power loss.

Regardless, I would not further complicate things by modifying anything else just yet - focus perhaps on plugging the holes and/or ECU tuning (but keep a backup of your stock fuel maps). As you said:

I might plug two of the six 8mm ports in the muffler and just experiment a little bit, but overall I am happy with what I have now.
 

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We've had this same cheap exhaust on my wife's bike for a few thousand miles now and had the same experience with the springs being too long but the welds and pipes actually looking pretty good. However after time the canister seems to look like this:
68577
 

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Best low-end and mid-range torque? Leave it bone stock. Long velocity stacks in the airbox, stock snorkel at the airbox inlet, relatively small-diameter exhaust header pipes, conservative cam timing. Just leave well enough alone. Yamaha knew what they were doing when they designed these. It's not designed for maximum possible top-end power, but it's designed for user-friendly ease starting off from a stop and mid-range torque (for what it is). "Low-end" is a misnomer ... Downshift.

No amount of fiddling with length can make up for header pipes that are too big for what you are doing with the bike. It just isn't going to happen.
 

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Best low-end and mid-range torque?...
Perhaps you can quote a message you're replying to - seems too ominous.

Also, I am curious if anyone has measured the exhaust flow rate, and what that measurement might tell about developing a custom exhaust.

I have wanted to get into experimenting, but I think @GoFaster has a good point (which I've agreed with before and have mentioned myself as the smart choice) - leave it stock. But again - that's no fun - I want to break stuff (and hopefully not destroy my motor in the process).
 

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I recorded this sound video with a cheap camera phone, it is best to listen to on a computer with decent speakers. This is what it sounds like after the modifications I made.


In my opinion, Stock header + CAT and no Muffler = very good deep bass tone.
(Note I did not ride the bike with this configuration, this opinion is restricted to the bike on a rear wheel stand only)

Stock header + CAT + Modified OEM Muffler has better deep bass tone than Stock Header + CAT + Stock Muffler
(Also slightly less engine braking if that is an issue)

Gatling style muffler straight thru with packing, I have no experience with this model. I like some engine braking and to design that into this style muffler can be tricky with a db suppressor or baffle from my experience with dirt bikes.

The OEM muffler is well engineered. I could use a little less engine braking though and the sound is somewhat mousy. I am happy with the sound and reduced engine braking. I may experiment a little more just for kicks. I am old retired fart locked up in the house so this was a cheap thrill for me.
 

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...
Gatling style muffler straight thru with packing, I have no experience with this model. I like some engine braking and to design that into this style muffler can be tricky with a db suppressor or baffle from my experience with dirt bikes.

The OEM muffler is well engineered. I could use a little less engine braking though and the sound is somewhat mousy. I am happy with the sound and reduced engine braking. I may experiment a little more just for kicks. I am old retired fart locked up in the house so this was a cheap thrill for me.
Essentially what you're saying: You like engine braking, but OEM exhaust is too restrictive, thereby inducing too much engine braking.
However, you're also saying you're happy with the results - more power to you, @kiko!

Preface the response with: If you know my argument is wrong, please give us reason & cite your sources.
Read on for an alternative solution to reducing engine braking.

On less restrictive exhausts
When removing the restrictions in your exhaust, you're not lessening engine braking.
Actually, you're reducing vacuum.

Less vacuum (and scavenging) explains why you need to be in 4th instead of 5th more often; less restrictions mean less torque and top-end horsepower at the same RPM (revolutions per minute) you were at, before the exhaust mods).

I found myself in 4th gear more often than before when I would have been in 5th gear.
If you really wanted reduced engine braking, (as far as I know), you would benefit from maintaining a restrictive exhaust but modify your ECU's stock emissions settings (with an ECU reflash service, FlashTune ECU, or aRacer RCMini5), one of which are: to DISABLE - "Decel fuel cutoff".

@Dreadwil has actually stated by using the aRacer RCMini5 (purchased from Norton-Motorsports.com I presume), Jesse from @Norton-Motorsports.com tuned @Dreadwil's configuration remotely (using remote desktop view).

You can learn the gist of the RCMini5 by visiting my ECU Tuning guide, specifically the Technologies > Intro to SpeedTek aRacer section.

When you disable Decel fuel cutoff, the stock ECU (or replacement aRacer RCMini5) will continue injecting fuel at or below a measured point in the TPS (Throttle Position Sensor) reading.
However, to regain torque and horsepower, you may get by with a tune via aRacer RCMini5 with Jesse's help.

On correcting AFR with narrowband O2 sensors
I do not know how much the ECU can tweak A/F mixture but on the way back the motor felt stronger as if the ECU had reset itself. That could be complete BS and just a seat of the pants observation.
You may be on to something there, @kiko.
I am not in tune with how the stock ECU corrects the wrong AFR, but what I do know is that aftermarket high-flow exhausts induce such drastic changes, it's outside the range of the narrowband O2, which is why people who desire the most control & performance buy autotunes (such as Bazzaz Z-AFM (and Z-Fi) or aRacer RCMini5 with AF1).

Granted, as @Dreadwil can attest; a knowledgeable tuner (such as Jesse from @Norton-Motorsports.com) utilizing just the aRacer RCMini5, and a conversation, can produce desired outcomes without autotune.

You may end up using more fuel & intake more air to maintain a fuel-air mixture as close to the ideal Stoichiometric (AFR) air-fuel ratio.
By the use of more fuel and intake of more air, you will experience a drop in MPGs (Miles Per Gallon).
 

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That is good information to know. I am not knowledgable about exhaust engineering but what you wrote makes sense, reducing vacuum. I popped the cap last night and I had drilled 7 not 6 holes, so as an experiment today I blocked 3 holes and will ride with 4 now. I did not try my top speed yesterday but I will today just out of curiosity to see if hp is reduced. I have dual sport tires on my moto so my top speed is only 100 mph. With the stock tires I was able to get up to 106 mph tucked. I fully realize to do any mods to the exhaust one needs a fuel programmer etc., but that is not feasible for me and I am too cheap to dump that much money into the MT-03. That is the main reason I do not buy a full exhaust. My riding is everyday but mostly just exploring or running errands, I seldom bounce off the tach red.
But I am having fun.
Thanks for the input. I am learning a lot, who says you can't teach an old dog new tricks??
 

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I'm going to take a guess and say you have lost low-end torque and lost top-end horsepower. If this is the case, then your top speed will be negatively affected (instead of 110mph, it might be more like 105mph hitting a rev limiter).
I'm not advising you ride to your top speed, by any means!
It's merely a figure to support the argument.

Before you ride
 

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Lost 5 mph on the top end. Engine braking improved on the bottom end by blocking 3 holes. Any changes to the exhaust will require a fuel programmer. Lesson learned. I am not interested in buying a slip on or a full exhaust now since there is no programmer in my budget. Back to the dirt bike, much more simple power management.
 

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@R3Wheelchair what do you think the purpose is with the exhaust chamber on this pipe (ebay)? Obviously they've got a baffle inside (or so it appears), but I wonder if there's actually any benefit to it.

This pipe ($143+ tax&shipping) and a slip-on may produce the performance gains without the cost of a premium system.

Going this route and using this Delkelvic slip-on would cost about $500 (much more than the Chinesium exhaust, but still less than the majority of brand name exhausts).

Repacking an oval pipe should be easier than any of the other oddly-shaped mufflers available.

I suppose the downside would be if I ever wanted panniers (pannier on the exhaust side would need to be shallow). Here's a Delkelvic Stubby 14" Oval slip-on.

i Thought it might act as an expansion chamber, but after trying it out with stock muffler or Akrpovic (sp) slip-on, I conclude to not waste your $ on it.
 

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i Thought it might act as an expansion chamber, but after trying it out with stock muffler or Akrpovic (sp) slip-on, I conclude to not waste your $ on it.
From what I've read (even though my writing may not reflect my current understanding (there's too much to learn with what little time I have)) is the shape of the exhaust must be conical from exhaust port to end of exhaust slip-on. This helps to reduce sound & gas reverberation; further pushing the exhaust gases out the tailpipe. Notice how the stock exhaust is also ceramic coated - while this may be to protect cheap steel long-term, this may also help exhaust hot gasses, by limiting the accumulation of heat on any given section of pipe.

All hot, pressurized air seeks cool, low pressure air. In theory, I suppose.
It's like pouring fluid into a cone; the fluid moves slower upon entering a narrower portion of cone; think of the exhaust pipe for the R3 in this way, but instead of pouring fluid in, you're pumping hot exhaust out - the velocity increases the further down the pulses get, but won't tend to bounce back to the narrower portions of the cone (enclosed space, reduced resonance).

Also - I'm an idiot, so I could be totally wrong. But maybe someone with more experience can confirm/deny it (I'm hoping they do).
 

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" the velocity increases the further down the pulses get" I would think the opposite, the gas pulse is cooling (contracting-slowing) the further down the pipe it gets and the size of opening is increasing for the given volume of exhaust, so velocity would be slowing.
 

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This model of Chinesium full exhaust is the one I keep finding works the best all around. Power-quality-EaseFitment. Here is the pix, if anyone has some time this weekend, try find which "Quality-brand" this pipe is copied from. ie M4-Agropovic-hindle-etc.
68622
 
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