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Discussion Starter · #21 ·
@Dreadwil bought this system from company ANODIZING, with 51mm O.D. (outer diameter).

If any of your decide to go with the Chinesium route, ensure the O.D. of the exhaust pipe outlet matches (or is within a few mm of) the I.D. (inner diameter) of the slip-on you purchase (if you buy the pipe and muffler separate).
The system I bought came with the muffler. The muffler that it came with is a very generic muffler that's found all over ebay on different exhausts for different bikes. But yeah, check the diameter as it's either going to fit an aftermarket full exhaust, or the OEM diameter which is tiny.

Regarding the packing, I've noticed a tiny bit of packing coming out the end of my muffler. Sometimes when I take the silencer out it will carry with it some of the packing debris. I'm hoping this is remnants/excess from the manufacturing process but I have my doubts. I haven't noticed any change in sound or heat (yet).
 

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The system I bought came with the muffler. The muffler that it came with is a very generic muffler that's found all over ebay on different exhausts for different bikes. But yeah, check the diameter as it's either going to fit an aftermarket full exhaust, or the OEM diameter which is tiny.
You're right about OEM being tiny... The downpipes (before the "collector" (which looks like a tweaker's bang up welding trick) and after the catalytic canister (I really don't even know if it's a cat)) are 1-1/8 inches which is 28.5mm (thank you RapidTables). However, I don't see that the aftermarket downpipes would be any wider than those, because these do merge at the collector, which usually converts to 51mm. On the product page, it does show the O.D. of your slip-on pipe is 51mm, so this (as I understand it) is what you must be referring to with regard to the "aftermarket full exhaust".

Hint: Maybe you can measure your Chienesium downpipes for the community and report back with the spec.

Regarding the packing, I've noticed a tiny bit of packing coming out the end of my muffler. Sometimes when I take the silencer out it will carry with it some of the packing debris. I'm hoping this is remnants/excess from the manufacturing process but I have my doubts. I haven't noticed any change in sound or heat (yet).
If some day you feel the need to, perhaps you could take some photos of the Chinesium pack job.

I appreciate the volume of the Delkelvic Stubby 14" Oval slip-on (204USD), and feel it would be the easiest to repack (perhaps using the Moose kit), and potentially will save me from becoming another obnoxious motorcyclist (noise annoys and deafens), so I will end up going with that if the diameters match up to the Chinesium mid-pipe. I emailed Delkelvic for the diameter on the Stubby 14" slip-on.

By the looks of it, I will need to purchase a 51mm slip-on adapter for the Delkelvic slip-on muffler; the picture has it legitimately connected to a stock system, which is 28.5mm; no bueno.

Hold the phone
By a mere click of a button, I found just the muffler: Delkelvic Stubby 14" Oval Muffler for a whopping 149USD. Now all I have to do is find a cheap slip-on 51mm adapter (maybe it's not even necessary). I can't keep track of my thoughts or my links, so I'm just going to link to a Yamaha R3 header pipe here.

Just discussing this makes me want to do the work just to see what it's like.
Essentially, I could have a cheap exhaust for 245USD (96USD header, 149USD muffler) and get it ceramic coated 130USD from Boneheads. That's without tax & shipping, of course - but I think it's worth the trial.

I've thought a little about the idea of just buying the Delkelvic system; I could probably have the shop where I get it ceramic coated to also install a M18x1.5-threaded bung for the Bosch wideband O2, since the bung placement on that system doesn't seem well-placed.

Exciting stuff here, @Dreadwil.
 

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Discussion Starter · #23 ·
I can measure the header pipe diameters for you in the weekend. From a glance they are definitely larger than OEM, but smaller in diameter than the later Akra / M4 / Graives headers. I believe the early Akra headers were smaller than they are now as they initially made them to cater for the R15 as well. They since increased the diameter after some R&D to get better performance out of the R3. If I were to guess, the Chinese copied the original (smaller diameter) exhausts, which is what I've ended up with.

I'm not going to open the muffler to check the packing but I know for sure they are very poor compared to a legit muffler. There are a few vids out there on YouTube where they cut open some Chinese mufflers to compare.
 

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Aloha, here are a few measurements for you:
Stock header outside, near head 28mm
Stock header outside going into muffler 31mm
Full exhaust header outside, near head 32mm
Full exhaust header outside, going into muffler 51mm

I wouldn't worry too much about the muffler, as they do little to quite on the stock system (the cat does 90% of sound reduction.) Best for looks and weight reduction.
And back pressure is needed for performance, and considering how much back pressure is produced in the stock system smaller diameter header pipe, restricting Cat, and small pipe going to the header, you can afford to put baffles into the full exhaust. In fact some full exhausts work better with baffles.
I prefer baffles that REDIRECT the exhaust all around and to the glass-pack of the muffler, rather than a baffle that just blocks the exhaust.
 

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So I experiment with baffles, knowing making back-flow may not be a big problem. I had one homemade baffle and the power was a bit more (or maybe not) and a little quieter.
But I did notice a significant power gain by using 2 Ebay baffles.
I will follow in your footsteps; I will buy two baffles and remove the Delkelvic baffle in the muffler.

I'm looking into the rolled baffle cones; there is a 51mm (probably good for the mid-pipe to slip-on, and perhaps I could find another for the downpipe to mid-pipe, but I feel this would cause the O2 from accurately reading the AFR. Tell me I'm wrong.

Aloha, here are a few measurements for you:
Stock header outside, near head 28mm
Stock header outside going into muffler 31mm
Full exhaust header outside, near head 32mm
Full exhaust header outside, going into muffler 51mm
Confirmed; the Chinesium exhaust has a similar diameter for the downpipes, @Dreadwil, as the stock system.
So the exhaust sort of acts like a cone; I wonder what diameter downpipes come with the brand name exhausts. I emailed GravesSport.com for more information regarding the Graves WORKS 2 full exhaust system.

I wouldn't worry too much about the muffler, as they do little to quite on the stock system (the cat does 90% of sound reduction.) Best for looks and weight reduction.
It sounds as though everything I read about mufflers this morning, you're claiming is wrong! Does it even make sense? The sound of a Coffman DeCat must be much louder than the sound of a muffler that is packed with fiberglass, right? Maybe I'm wrong, but I feel like you're wrong here.

You're right; I misread the message.


And back pressure is needed for performance, and considering how much back pressure is produced in the stock system smaller diameter header pipe, restricting Cat, and small pipe going to the header, you can afford to put baffles into the full exhaust. In fact some full exhausts work better with baffles.
I prefer baffles that REDIRECT the exhaust all around and to the glass-pack of the muffler, rather than a baffle that just blocks the exhaust.
A-firm. I sense you are right about this; it doesn't make sense to completely delete all restrictions with a completely straight-thru full exhaust. I once drove my truck without any pipe from the header downpipe (canceling out the two catalytic converters), and there was no torque. It was loud and annoying, however.

I emailed Delkelvic, asking them for diameter of their downpipe on this full system.
 

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Discussion Starter · #26 ·
Benny, Jesse has done a comparison of a newer full exhaust compared to an earlier full exhaust designed for the R25, but also sold for the R3 at the time. The older exhaust is much more similar to my chines copy.

Image of comparison: https://www.norton-motorsports.com/wp-content/uploads/2015/05/m4-vs-akra-pipes.png

Full article: Yamaha YZF-R3 / MT03 exhaust dyno test and superbike build. How much power does the R3 make?


I recommend having a read of some his blogs. There's no other freely available information out there that's as comprehensive and as knowledgeable.
 

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Chinesium header is much larger 30% larger.
Doubt baffles will affect the AFR reading.
Choosing a baffle to divert the exhaust to the glass-pack and re-directing rather than just Backing-up the exhaust to me is key. Gives best back pressure to silencing ratio.
Historically, mufflers with chambers and not glass packed are more quiet.
You want to put a baffle in a place right after the pipe gets bigger (expansion), (so the back pressure caused by the baffle does not cause the exhaust to slow or "stiffle") but the cuts the sound down.
 

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I am missing something here, why is the bung hole location not optimal with the Delkevic? Can the bung hole register O more accurately further downstream of the collector? Is there data to support that?
 

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I went on a tangent and compiled a motion of quotes from the article you linked, @Dreadwil. It took me a minute to get through it all, but **** - that was a good read.

You can see my notes here

On my dirt bikes I experimented several different ways to reduce noise while not impacting performance. The best results I ever achieved was to purchase some expanded metal and roll it into a coil like in the photo above. I then secured it into the muffler outlet with a piece of wire across the diameter. The expanded metal had a length of about 65mm about 2 1/2" if I remember. The upside to the DIY application is that you could roll the expanded metal in a tighter roll for more noise suppression if you wanted.
I have a few tests in mind with the method @kiko used with 65mm DIY baffling rolls, and the method @R3Wheelchair used with baffle inserts, knowing what I do about the R25 and asian pipes repackaged for the R3, thanks to @Dreadwil.

Here's an anecdote from The Man himself:
...I, and other tuners have seen over and over again, which is the fact that the R3 performs better with the noise restriction silencers installed in the exhaust, and always seems to be down on power with exhausts that are completely unrestricted in the end.
excerpt from his article
I'm still considering going the Delkelvic full exhaust route. I'd have to re-place the bung further down the pipe, closer to the slip-on; doing this should also provide clearance for the collector beneath the oil pan and allow for me to place the O2 bung according to Bazzaz's and aRacer's AF1 spec'd angles. Pictures in below spoilers (best viewed on desktop).

 

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Discussion Starter · #30 ·
I am missing something here, why is the bung hole location not optimal with the Delkevic? Can the bung hole register O more accurately further downstream of the collector? Is there data to support that?
Possibly? But I'd say it's more likely the fact that they use the same mid pipe for many bikes, so it's not going to align the same for all.
 

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I understood to keep the sensor as far from the exit of the exhaust as possible to keep the fresh air from mixing in and messing with the readings.
 

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From what I can tell so far is that
  • Muffler packing is not the same as baffle wrapping
  • Wrapping baffles is dependent on the type of baffle being used
    • All baffles are designed to be placed inside the muffler baffle
    • Some baffles may fit in exhaust tubing
  • I think "silencer", "baffle", and "db killer" are all the same things

Here's an article on Pros & Cons of Exhaust Baffles, where they summon the mythical "back pressure", which to them is "bad". From what I've learned, "back pressure" is a myth; a more correct term is "restricting exhaust flow rate". The restriction of exhaust flow isn't necessarily a bad thing (unlike what most sources of information will have us believe).

As far as I understand, restricting the flow of exhaust allows slower air & fuel delivery systems to match the standardized rate of vacuum in the exhaust (or the exhaust flow rate), thereby maximizing torque based on this equalized vacuum throughout the engine.

@R3Wheelchair claims:
"You want a baffle before an expansion point where the tubing is greater diameter, such as
  • downpipe to collector, or
  • collector to mid-pipe, or
  • mid-pipe to slip-on
Placing a baffle before the expansion should prevent the exhaust flow rate from being affected."

What I believe @R3Wheelchair is suggesting (where the "expansion point" might actually be a "condensing point" (where the exhaust pipe diameter changes)):



What I'm seeing is, baffles that are designed to be wrapped should never be placed inside the exhaust tubing; they should only be placed inside the muffler baffle.

These are baffles designed to be wrapped in muffler packing:


Placing the baffle inside the (for instance) collector or mid-pipe will cause two things:
  • Burnt baffle wrap, and/or
  • Annoying rattling
I've drawn up a basic diagram showing the difference from the "muffler baffle" and the "baffle insert" to show where the (above) baffles should be installed.
  • Wrapped baffle (blue)
  • Baffle insert
  • Muffler baffle
  • Muffler packing
 

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Because I got the ominous error:



I will just write another post...
And I'm sorry for thread jacking, but I swear it's all well-intentioned; it's not lost.

I got two emails back from Delkelvic and as an update to the section of this post:

I appreciate the volume of the Delkelvic Stubby 14" Oval slip-on (204USD), and feel it would be the easiest to repack (perhaps using the Moose kit)...so I will end up going with that if the diameters match up to the Chinesium mid-pipe. I emailed Delkelvic for the diameter on the Stubby 14" slip-on.
Regarding the silencer packing and slip-on piping diameter
bennyrides:
I'd like to know all the tech specs on the KIT04DY, at
Stubby 14" Stainless Steel Oval Muffler to fit YZF-R3 (2015-2020)

Specifically, muffler packing material & method, and slip-on pipe diameter.
Thank you for your time.
Delkelvic:
Thank you for your interest in Delkevic products. Our mufflers are fiberglass packed and they are repackable. Blind rivets are used to secure the inlet and end caps to the canister. We sell repacking kits on our website that include packing material, replacement rivets, sealant, and clamps. The link pipe and internal muffler diameter is 2 inches [which is 50.8mm or simply 51mm].
Regarding the downpipe diameter of their full exhaust
I emailed Delkelvic, asking them for diameter of their downpipe on this full system.
bennyrides:
I have a question regarding the COM09BB.

What is the diameter of the downpipes used in this kit?
Full System to fit YZF-R3 (2015-2020) with Stubby 14" Carbon Fiber Oval Muffler and Stainless Steel Header

If there a technical spec sheet, I'd like to share it with a public forum if I could have your permission for that.
Thank you for your time
Delkelvic:
Thank you for your interest in Delkevic products. The down pipe diameter is 35MM. I have attached dyno graphs for various silencers. The length of the silencer is indicated on the graphs.
Delkelvic downpipe dimension
The downpipe from Delkelvic starts at 35mm. This was data to enhance this response:
Aloha, here are a few measurements for you:
Stock header outside, near head 28mm
Stock header outside going into muffler 31mm
[Chinesium] Full exhaust header outside, near head 32mm
[Chinesium] Full exhaust header outside, going into muffler 51mm
...
This data confirms
  • (what @Dreadwil mentioned) the Chinesium exhausts were designed to be used on the YZF-R25 (250cc) (as also mentioned in Jesse's write up here:
    Early tests of the stainless steel Akrapovic full system were a bit underwhelming, and I came to soon learn this was because the exhaust was originally developed for the R25 in Asia, which is why it was first to market. A couple years later, Akrapovic redesigned the system for the R3 and the new system also features a carbon fiber muffler can, so it’s easy to distinguish which system you are getting.
    Yamaha YZF-R3 / MT03 exhaust dyno test and superbike build. How much power does the R3 make?
    • The Chinesium R25 exhaust features a 32MM downpipe
    • Many Chinesium exhaust designs may have been copied from the early Akrapovic Stainless Steel for the R25 (theory originally claimed by @Dreadwil)
    • Interesting fact: Akrapovic full exhaust systems for the R25 and R3...are the same exhaust models (see below):

      Technically: All R25 exhausts should fit on the R3 (as we already are aware with the Chinesium exhausts @Dreadwil and @R3Wheelchair use on their bikes)
  • The Delkelvic full exhaustis actually designed for the YZF-R3 (321cc)
    • The Delkelvic downpipe features 35MM
  • And taking from the data you'll see below: The size of the silencer (muffler/slip-on) produces nearly identical results to maximum power output on de-cat systems
    • Size of slip-on doesn't matter (from Delkelvic)
    • I replied in the email asking if the dyno results included any ECU modifications or fuel map tuning
  • Here's a theory: These exhausts (the ones designed for the YZF-R3), whose downpipes are at least 35mm in diameter, may provide better low-end, as restricting such exhausts with proper baffles should provide a greater reduction to exhaust flow rate, while still providing the volume for more efficient scavenging.
bennyrides:
...My research has led me to the realization that a chinese knock-off may dramatically increase performance, based on the fact that OEM downpipe & collector are 30% smaller than the Chinese knock-off (32mm).

Which means the dyno Delkelvic de-cat results will be inferior to the repackaged Chinese exhaust designed for the YZF-R25 (a 250cc motor). There will also be better flow, due to the engineered design of the R25 exhaust system, whereas the R3 OEM exhaust isn't designed with efficiency.


The Delkelvic full exhaust (whose downpipes are 35mm, as you've told me) may increase performance further, but because these exhausts are designed for racing, it may not actually benefit riders who want their R3s to excel in low-end and mid-range torque.

However, as enthusiasts have regarded (such as Jesse from Norton-Motorsports): The R3 doesn't perform well without exhaust flow rate restrictions.

Exhaust flow rate restrictions for the R3 require vacuum via scavenging to produce its torque; the Delkelvic exhuast system (35mm downpipe) without restrictions will ultimately decrease low-end and mid-range torque.

What are your thoughts?
All the Delkelvic Representative could reply with is, "I am of the opinion that the dyno results are sufficient evidence that the complete system increases power throughout the RPM range."

De-cat dyno sheets
These dyno graphs of de-catting show nearly identical max power increases, but also it appears there are variations through the power curve (which may or may not be caused by the different silencer lengths).

Also, here's an important detail on Delkelvic's dyno sheets: they are charted with the STD measurement, not SAE (industry standard).

Jesse goes into detail on his lengthy post, and here's the first part regarding this marketing "gimmick":

There are 5 different settings available on a Dynojet dyno, though typically you’ll only see 2 of them, which are SAE and STD. SAE is the current industry standard, but a lot of tuners will still print dyno charts in STD correction because the numbers are always higher, which is a bit misleading to customers.
Yamaha YZF-R3 / MT03 exhaust dyno test and superbike build. How much power does the R3 make?
So technically speaking, Delkelvic is sharing charts that don't represent an accurate power increase readings - and that's throughout all of their product pages - all of their dyno charts have a Correction Factor in STD.

Being that their readings are from using de-cat and slip-ons (and they haven't told me if they've tuned the motor), these charts are pretty much useless.


Food for thought.

File PR2735 200MM
"Delkelvic de-cat 200mm"


File PR2735
"Delkelvic de-cat 350mm"


File PR2735 450MM
"Delkelvic de-cat 450mm"
 

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This pretty much sums up everything I've learnt about exhaust (in regards to the YZF-R3) in the past three days:

It really doesn't matter which silencer (muffler/slip-on) you use. What does matter:
  • the diameter & design of downpipes, collector, and mid-pipe
  • how much exhaust flow is restricted with baffles and db killers, and
  • how it's tuned to that adjusted rate of vacuum
  • oh, and reference to "back pressure" is a line of crap
Sorry @R3Wheelchair and @Dreadwil and @kiko for thread jacking...
This concludes the extent of my research and confusion regarding exhaust.
 

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You are scratching the surface and getting somewhere ... (and I don't claim to be a subject matter expert myself, although perhaps I've been scratching that surface for a while now)

Intake and exhaust system flow is not steady state - far from it. It is a train of pulses that travel at the speed of sound inside whatever chamber or pipe is containing them. Complicating that ... especially on the exhaust side, the speed of sound is not a constant. It is a function of temperature (specifically, it is in proportion to the square root of the absolute temperature), and that means it's high near the cylinder head and drops off as the gases lose heat as they pass down the pipe. So the diameter matters but also the length of each pipe section matters. The length affects the amount of time a pulse travels down the pipe, reaches a junction or expansion which reflects it back up the pipe as an expansion wave, and then travels at the speed of sound against the direction of flow (important!) back up the pipe towards the engine, and hopefully that pulse arrives back at the engine at some time that is useful (e.g. during the short period of time when the exhaust valve is not quite closed and the intake valve has just started opening - "overlap" at TDC between end of exhaust stroke and start of intake stroke).

The header pipe generally has a length such that near the maximum-power RPM, that negative pulse arrives near the end of the same exhaust stroke that initiated it (roughly half a crankshaft revolution - perhaps a little less).

The complication is that this isn't the only thing going on in there. After the pressure wave passes that junction in the collection, it may be reflected back up that header pipe as a negative wave, but it continues down the mid-pipe and up the OTHER header pipe as a positive wave. When that positive pressure gets to the closed valve in the other cylinder, the pressure wave has nowhere to go, and gets reflected back down the other cylinder's header pipe as a weaker positive wave. Meanwhile the one going down the mid-pipe reaches an expansion in the stock exhaust system's collector/catalyst box and that gets reflected back upstream as a negative wave. An aftermarket exhaust doesn't have that collector-box but eventually that pulse gets to the muffler which acts like an expansion as well.

All these waves get superimposed on top of each other and the net result is a really, really, really complex hard-to-analyse mess. On top of that, you have the fact that this engine has an uneven firing pattern. One cylinder fires, then the next one half a crank revolution later, then there's 1.5 revolutions until the next one. These wave reflections don't just affect the end of the same cylinder's exhaust stroke, they also affect the next cylinder in the firing order, and the one after that ... It's complicated. Something about this complicated mess leads to some of these wave reflections turning out to be undesirable, which may have something to do with why these engines seem to like having a quiet muffler on them.

As an aside, the Hindle exhaust system on my bike uses header pipes with a nominal diameter of 38.1mm (1.5 inches), and after the collector 50.8mm (2.0 inches). I am quite convinced that these diameters are chosen for one simple reason, "that's the way they build all of their exhaust systems unless it absolutely can't be done that way". Yamaha R1? Same diameters. Yamaha R6? Same diameters. It's easier to manufacture. I suspect something with enormous cylinders, like a Ducati twin, might differ. But by default ... that's the way they're built.

A decently-healthy R1 or other 4-cylinder superbike makes about 45 horsepower from each cylinder (the horsepower is very close to in proportion to the mass-flow-rate of air/fuel/exhaust through the engine). We make half that. I'm pretty sure Hindle's diameters are too big for the engine. A header diameter that is too small will restrict the flow out of the cylinder, which is very bad. A header diameter that is too big will weaken the effect of the pressure waves, which is sub-optimal but not horrible. So, Hindle makes them somewhat too big by default.

The right configuration is probably stepped or tapered, starting at whatever the diameter is at the port in the cylinder head, and then stepping up at carefully-chosen positions down the pipe to manage what the pressure waves are doing. But that is not simple to manufacture...

Some exhaust systems have a little cross-over pipe partway down the header pipes ... that acts like a controlled expansion point. I've seen some for the R3 that are clearly using smaller-diameter header pipes than the Hindle uses, but with a cross-over pipe. I've seen some stepped/tapered ... I think the Graves is like that, but no Graves exhaust for me, $ $ $ $ in Canada. (I chose the Hindle because they are built locally, there is ample local support, and they are a long-time sponsor of Canadian roadracing.)

Yamaha put reasonable design effort into the stock exhaust system. They have emissions and noise constraints to keep in mind, but also driveability, mid-range torque, etc. For a street bike ... if you are not necessarily in search of every last bit of top-end horsepower ... "leave the darn thing alone" will not be far wrong. And it's certainly cheaper ...
 

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Yamaha put reasonable design effort into the stock exhaust system. They have emissions and noise constraints to keep in mind, but also driveability, mid-range torque, etc. For a street bike ... if you are not necessarily in search of every last bit of top-end horsepower ... "leave the darn thing alone" will not be far wrong. And it's certainly cheaper ...
After reading many threads about exhaust options, I decided tonight to remove the OEM muffler and fire the bike up so I could listen to the sound with only the CAT and OEM header. A very nice deep tone without all of that other rattling noise in the background. 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. I drilled out about six 8mm holes in a circular pattern around the 25mm outlet tube. I thought if the experiment went bad, then I could always plug those holes or pack insulation under the cap to block the 8mm holes.

Then I reinstalled all of the parts and fired the bike up again. I do not do track days or chase tail lamps of R1 riders so no need for me to try to squeeze out 2 hp with a $400 full exhaust. But I do really like the new deep tone of the modded exhaust.

I appreciate all of the hard work and info that I have found on this board to learn about how exhausts are engineered. A fascinating topic.
 

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First of all - thank you @GoFaster for sharing your beautiful brain with the rest of us. I love the contents of your grey matter.
This is going to prolong the thread jacking, but still, @Dreadwil; it's all well-intentioned, and might I add - I appreciate you making this thread, because without doing so, I wouldn't have been able to learn so much about the dastardly YZF-R3 exhaust system (and all the aftermarket shenanigans that come with it).

I without a doubt thank you for all the information you've provided on exhaust gas pulsation and the complicated mess it all is - there are many great points you've brought up that seem like sound evidence.

I'm really interested in a few particulars:
...the speed of sound is not a constant. It is a function of temperature (specifically, it is in proportion to the square root of the absolute temperature), and that means it's high near the cylinder head and drops off as the gases lose heat as they pass down the pipe.
I feel like you're merely referring to high pressure and low pressure here. Sensibly, the highest pressure in an exhaust system should be just outside the exhaust port on the engine's cylinder head; while the lowest pressure should be at the outlet of muffler leading to the atmosphere (outside air). I read you - on the bits of where the exhaust gas is never ceasing to find the low pressure areas, thereby complicating exhaust gas flow directions and doubly-so when there's more than one head pipe in the mix.

and hopefully that pulse arrives back at the engine at some time that is useful (e.g. during the short period of time when the exhaust valve is not quite closed and the intake valve has just started opening - "overlap" at TDC between end of exhaust stroke and start of intake stroke).
How could an exhaust pulse that arrives back at the cylinder head be "useful" to scavenging (overlap)? Am I even using the term "scavenging" correctly (I don't know anymore)?

The header pipe generally has a length such that near the maximum-power RPM, that negative pulse arrives near the end of the same exhaust stroke that initiated it (roughly half a crankshaft revolution - perhaps a little less).
...
All these waves get superimposed on top of each other and the net result is a really, really, really complex hard-to-analyse mess.
...
which may have something to do with why these engines seem to like having a quiet muffler on them.
I quoted this just because it's interesting. Bite me.

"that's the way they build all of their exhaust systems unless it absolutely can't be done that way".
...
I'm pretty sure Hindle's diameters are too big for the engine.
So I just realized this is the same case with Akrapovic; the R25 and R3 exhausts are the same product, granted the difference between 250cc and 321cc is negligible compared to the 2015+ R1 at 998 cc (source) and the 321cc of the YZF-R3. However, Jesse claims the following:
A couple years later, Akrapovic redesigned the system for the R3 and the new system also features a carbon fiber muffler can, so it’s easy to distinguish which system you are getting. I picked up a carbon Akrapovic system to retest.
Yamaha YZF-R3 / MT03 exhaust dyno test and superbike build. How much power does the R3 make?
A header diameter that is too small will restrict the flow out of the cylinder, which is very bad. A header diameter that is too big will weaken the effect of the pressure waves, which is sub-optimal but not horrible. So, Hindle makes them somewhat too big by default.
Is it possible that the larger Hindle could produce better low-end torque with a number of baffles and db killers to reduce the exhaust flow rate, thereby enhancing the scavenging effect (slowing down exhaust pulse velocity to match the stock R3 air & fuel delivery systems)?

The right configuration is probably stepped or tapered, starting at whatever the diameter is at the port in the cylinder head, and then stepping up at carefully-chosen positions down the pipe to manage what the pressure waves are doing. But that is not simple to manufacture...
I agree; the R&D for a custom R3 exhaust would simply be too costly for what the R3 is.

if you are not necessarily in search of every last bit of top-end horsepower ... "leave the darn thing alone" will not be far wrong.
But that's no fun, @GoFaster.

It's interesting to know a Hindle header has
  • a nominal diameter of 38.1mm (1.5 inches)
    • The "stock" and "Chinesium" dimensions were spec'd by @R3Wheelchair, see post
    • The stock header is 28mm
    • The Chinesium edition headers are 32mm (designed for YZF-R25s)
    • The Delkelvic headers are 35mm (designed for the YZF-R3)
  • and after the collector 50.8mm (2.0 inches)
    • This is the diameter of most aftermarket slip-on pipe diameters, so it makes sense they've designed their pipe work to connect with other aftermarket slip-on
    • The "stock" and "Chinesium" dimensions were spec'd by @R3Wheelchair, see post
    • The stock mid-pipe to slip-on fitment is 31mm
      (51mm to 31mm adapters come with most slip-ons, as seen in the image below)
    • The Chinesium edition mid-pipe to slip-on is 51mm
    • The Delkelvic link pipe (mid-pipe to slip-on) and internal muffler diameter is 50.8mm or (simply 51mm)
I suppose the real test would be similar to what @R3Wheelchair is doing with the collection of baffles and header pipes he's got.

I feel like I should be joining in on the madness, developing a street exhaust system that is tuned to preserve fuel & perform on-demand.
Maybe I could fabricate a high-flow catalytic converter. I dunno - but this all seems worth it.
 
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