The creators of the 390 Duke, KTM, designed a compact, mass-centralized exhaust system that was carefully synchronized with the ECU's fuel mapping. As MalJohann notes, any change to the exhaust will perturb the air/fuel ratio programmed into the ECU: and this could lead to an excessively lean condition which could seriously damage your motor. KTM has approved the Akropovic exhaust as an aftermarket upgrade. But to use this exhaust also requires the ECU remapping reflash KTM offers.

I think your best bet is to leave the well-designed stock exhaust alone and not worry that it has a civilized exhaust note, as Mechanical_Vandal advises. A 390 Duke is never going to rumble like a Harley!

The Duke exhaust is one of my favorite features of the bike. It is centralized, compact, unobtrusive and effective. It does not require hanging a conventional-style can off the side of the bike - in addition to requiring a remap, this arrangement interferes with saddlebags, precludes (or burns) a pillion, creates extra aerodynamic drag to slow you, and is waiting to be mangled if there is a crash. The "cheap/safe/good" exhaust you are seeking is the one you already have!

 

This thread seems to perpetuate the myth that an open pipe or one with less internal obstructions merely needs fueling changes to outperform the stock design. It is not nearly as simple as that and even reputable companies only sell replacement systems that are dyno proven to produce the same power as stock. They may claim slightly more torque in parts of the rev range but can almost never produce significantly more top end power.


The standard exhaust is designed to have an effective length which is matched to cam timing and other engine parameters and it operates in a resonant way which is completely broken if you remove its internals or replace it with an open pipe.


The exhaust design of this bike is one of its best features for exactly the reasons described above and in my opinion even the factory approved alternative is no improvement except for a better sound.

 

If you want to be heard for safety, a better alternative to a loud exhaust is to fit a good set of aftermarket horns, such as FIAMM, Hella, Denali, etc.

 

I ended up buying a stock exhaust for peanuts from a guy who'd ditched it for an aftermarket one. The plan is to use it for experiments to see if anything can be done to improve the tone while making the least changes to the existing design, but life is getting in the way of being able to spend much time on it.

I have done some exploratory keyhole surgery already to see what the innards really look like & have some ideas to try... just need the time to do them.

 

Peter, I'm glad you had a chance to read the long thread by Formula390 documenting his prolonged but ultimately unsuccessful efforts to create an alternative to the OEM underbody exhaust. Knowledgeable people who have studied the stock exhaust are genuinely impressed by its engineering and effectiveness. This is a very cleverly designed piece that extracts excellent power from the engine, emits a civil exhaust note and meets developed country pollution standards, all in a compact, mass-centralized unit that is nearly invulnerable to crash damage and does not interfere with luggage.

Sadly, this highly-developed product of KTM's engineering team is underappreciated by a sector of 390 owners: it is most often maligned for being too quiet and vilified for not producing a more raucous exhaust note. (NB. I just learned from watching a YouTube evaluation of the new 2017 Duke by an Indian tester that the new exhaust reportedly was necessary because the 2013-16 exhaust could not meet Euro 4 NOISE standards - the outgoing stock exhaust was sufficient to meet the emissions standards but was TOO LOUD!!) Those who criticised the Gen 1 exhaust's moderate tone will find even more fodder for frustration with the new 2017 unit! Still, many 390 owners have been eager to spend large amounts of cash on aftermarket cannister exhausts that are only marginally lighter, produce little if any gains in power/torque, require an expensive fuel controller to protect the engine, and are very vulnerable to crash damage. The chief "benefit" of these exhausts seems to be that they are less successful than the stocker at dampening exhaust noise.

To my mind, really the only sin of the Gen 1 stock exhaust is that it is rather heavy - about 14 lbs (6.4 kilos). Likely for reasons of production costs, the whole unit is fabricated from mild steel, rather than alloy, resulting in a somewhat hefty lump - but still much lighter than the 2017 stock exhaust.

To date, the only worthwhile potential candidate to replace the Gen 1 stock exhaust - IMO - has been the Werkes Competition unit, a small underbody canister that fits in the OEM location. The Werkes is very simple and lightweight, reportedly saving about 10 pounds over the stocker. Reports about its effect on power are unclear, but certainly it will require a fuel controller. Until recently the Werkes was considered unacceptable because, as delivered, the unit has no sound packing and is extremely loud. However, some recent experiments with disassembling and packing the Werkes reportedly have been quite successful. Our colleague CDN Duke is presently testing a packed Werkes on his bike and appears to be pleased with early results. We will have to see how durable the packing may be. So if you are interested in saving weight over the stock Gen 1 exhaust, the Werkes, IMO, is your best candidate. Stay tuned. But you will have to be prepared to fit a controller.

 

To date, the only worthwhile potential candidate to replace the Gen 1 stock exhaust - IMO - has been the Werkes Competition unit, a small underbody canister that fits in the OEM location. The Werkes is very simple and lightweight, reportedly saving about 10 pounds over the stocker. Reports about its effect on power are unclear, but certainly it will require a fuel controller. Until recently the Werkes was considered unacceptable because, as delivered, the unit has no sound packing and is extremely loud. However, some recent experiments with disassembling and packing the Werkes reportedly have been quite successful. Our colleague CDN Duke is presently testing a packed Werkes on his bike and appears to be pleased with early results. We will have to see how durable the packing may be. So if you are interested in saving weight over the stock Gen 1 exhaust, the Werkes, IMO, is your best candidate. Stay tuned. But you will have to be prepared to fit a controller.

Packing options are being discussed here: Packing Werkes Exhaust + Dyno!

Note that the Werkes pipe does come with packing from the factory, but the original packing doesn't tend to last long. Mine has been repacked by Competition Werkes with a ceramic material rated at 2300 degrees. Not sure if this is upgraded from when they first released the pipe or not. However, it is quite common for these to blow out the original packing in relatively short order. Competition Werkes will repack at no charge, you just need to pay for shipping. When packed, I think the pipe sounds great but it is admittedly on the louder side.

 

Buddy of mine had Dual Supertrapp's on his 1985 V-Max and a Dynojet Stage 3 carb kit done at local Dynojet facility here and when they had it on the dyno his neighbors started coming over to see what the H**L he was tuning ! I rode it and next to my K1300s it was the fastest bike I've ever ridden. Was definitely the loudest by far !

 

Hi Johann,

Any updates on fitting your SuperTrapp ?

 

I'm curious to see how the Supertrapp muffler works, too.

 

Inquiring minds want to know, Johann! The pressure is building....
We know you have other priorities, such as the O2 sensor. But if the SuperTrapp works (without being obnoxiously loud), and the fuelling can be correctly mapped with a piggy, I think many would be interested in that mod.

Despite its rather stifled tone and ample mass, the stock exhaust is so well engineered that - as Binoy the PowerTronic guy affirmed - it is extremely difficult to find any aftermarket exhaust that can beat the stocker for power.

 

Inquiring minds want to know, Johann! The pressure is building...

[DISCLAIMER] Super busy on all fronts of life at the moment, so projects and participation on the forum is less of a priority and not so desirable time allocation wise. I'll let you know how it turns out when I get to it, but there's no reason it shouldn't be the perfect tunable and tucked away solution. [/DISCLAIMER]

 

Unless there's a after market that tucks up like the stock I'll wait...

That said, very interested in the install...

 

GPR Ghost...

 

One drawback of any aftermarket company making a compact underbody similar to OEM is the short header length and its detrimental effects on power. I fully understand not wanting a can hanging off the side, but we're making over 40% more power in the midrange with the MIVV, so that's a trade off I'll gladly accept. It's just too fun.....

 

Funilly enough... yes ! Waxed once, washed, vacuumed & interior detail twice. Am I a clean-freak or what ! And then there's the 3D Printer.....

 

In creating the 390's underbody exhaust, KTM evidently did a thorough job of research and testing, ending up with a system that contributes in a major way to the engine's class-leading power output. The principal feature of this exhaust is a carefully-tuned header and exhaust length such that the resonant frequency of the exhaust pulse waves helps scavenge the exhaust gasses, leading to better cylinder filling/more power. KTM engineers did their homework and produced a very successful component in terms of power extraction from the motor. Unfortunately, very likely for reasons of cost, it was decided to build the exhaust cannister out of mild steel, resulting in a rather heavy lump which could have been significantly lighter if built with other materials.

The video posted by Sinha shows a Duke owner, in a quest for "better sound/more noise" amateurishly cutting a hole in the the exhaust cannister. The probable result of this uninformed intervention is to disrupt the resonant frequency of the tuned exhaust system. Undoubtedly, if this bike were tested on a dyno, first measuring power with the intact OEM exhaust, then comparing this with the altered exhaust's performance, the latter would show a power loss.

Exhaust design is a complex engineering project that draws on several sub-disciplines of physics. It is not for amateurs, or even for aftermarket companies without the necessary design and testing resources. Just to illustrate the difficulties of exhaust design, read the thread below from the RC forum, describing Formula390's efforts to build a lighter, better sounding, more powerful underbody exhaust for the 390 engine:

Exhaust development work

 

Understood Diploman, it's why I was asking if a hole was placed in the spot as shown in the video, what do we think would be the impact, after comparing to the dissection views previously shown. I need to take a closer look at the opened exhaust, it's possible a hole here actually bypasses the full reroute through the catalytic, but I can't be sure yet due to limited time to carefully review the pics.

 

@Diploman; I followed your recommendation and spent the last 1-2 hrs studying the RC 390 "Exhaust development work" thread. (We can now we're retired). That is some amazing R&D and absolutely nails what you have been telling everyone. "The stock (2013-16) exhaust is a masterful work of very complex engineering". My interest isn't sound or power it is weight. I would like to get rid of the cat which is heavy and not required by legislation down here. Having read Formula 390's comments on his decatting experience I accept that's in the too hard basket for me. Going for a lighter product using the existing geometry just increases noise with zero performance gain and more likely performance decrease. What is really interesting is that the 2017 has this additional exhaust, clearly to meet Euro legislation, that can only be detrimental to performance and detracts from the original design genius..

 

I've been watching a stock exhaust on eBay for the purpose of modification. Any modification to it will change the power delivery and require fuelling changes. Without fuelling changes you risk blowing the engine.

 

I have to add that I wouldn't do what they did though, that's just heresy, might as well run a straight through.

 

can u suggest me a cheap / safe / good exhaust system?
i'm very much happy with the duke 390 except the exhaust note!
:crying:

 

There are lots out there that'll make it sound better. If I were you, I'd look at getting a PowerTronic and air filter first though.

Not so many that'll make it faster though. I'm keeping my quiet stock exhaust fitted to my bike and my money in my pocket and just laughing at anyone that thinks my bike will be slow because it's quiet.

 

I totally agree with all the comments above, Noise does not always = power & as mentioned changing the exhaust may not give you more power, More than likely with more flow you main gain power higher in the RPM range but you might actually lose needed torque & power down lower in the revs, This is the tricky part that needs to be worked out by a good exhaust manufacturer

1 of the main advantages though even if you dont gain any power is the weight loss, The stock catalytic converter is rather heavy so dropping the weight helps your power to weight ratio overall which not only helps acceleration but also braking & handling, Probably barely noticeable to most unless you are racing & going for those extra seconds per lap etc

I am waiting to get my hands on the new Austinracing Hi Slung GP1 exhaust as soon as it is available>

https://www.facebook.com/pages/Austinracing/654737234631379

 

don't forget the famous tunable Supertrapp

SuperTrapp: Performance Exhaust


These really work as advertised. I've had one on my Mini Cooper S for along time and will install one on my next motorcycle (last bike was a 2 stroke.)

 

i'm happy with the speed, not looking for any kind of performance boost..
only looking for a better exhaust tone...

 

After much research and consideration I've decided to go with the SuperTrapp S/C Elite 10" stubby in the OEM location in place of the original exhaust. This, only because I can adjust fueling with my aftermarket piggyback ECU, but having a flow adjustable exhaust will certainly help too.

http://www.supertrapp.com/product_sections/detail.asp?CatID=30&ItemID=443-2011

 

After much research and consideration I've decided to go with the SuperTrapp S/C Elite 10" stubby in the OEM location in place of the original exhaust. This, only because I can adjust fueling with my aftermarket piggyback ECU, but having a flow adjustable exhaust will certainly help too.

SuperTrapp: Performance Exhaust

MJ! One more thing for you to review for us! Will look forward to your install!

 

I'll be interested to see how this works for you. If you can fit it in the OEM location, it will retain all the "packaging" advantages of the original, plus likely lighter weight. Possibly might gain a HP or two if the fueling can be sorted. Nice choice!

 

4” Disc S/C Elites are a 3.5” body diameter which tapers out to a 4” opening. They’re available in a 10” length body with a 2.00” (50.8mm) inlet diameter (ID).

This is smaller than the original, and because its the same shape all around and exhaust gasses exit at the opening around its diameter, you just rotate it until the mounting bracket lines up (may need to bend the bracket a bit, but its SS so bending is fine) to the mounting point on the frame.

Also, in case you missed it, the exhaust can be tuned to your bike, or in combination with a piggyback ECU to how you want the power curve to look. Essentially because the discs are separated by a gap, by adding more discs at the opening, you increase the size of the opening. It helps to think of each disc you add as making another hole in the exhaust, or making the current one bigger.

Have a look at their FAQ: SuperTrapp: Resource Center

[EDIT] My thanks to @flyboy2160 for putting me on to the Supertrapp exhaust! [/EDIT]

 

I like that "tuneable" concept. Thank you for being the Guinea Pig! Hope it turns out to be a valuable upgrade. If so, I might emulate...

 

I like the GPR underbody exhaust.
looks even more compact and simpler than the OEM.

https://www.youtube.com/watch?v=UzMyanqmy0I

 

I love where the stock exhaust is situated, would happily keep it. But.....it's not loud enough. And my main reason is safety. Nobody can hear you.