[Diploman]

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!

 

[Diploman]

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!

 

[Diploman]

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...

 

[Diploman]

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.

 

[Diploman]

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.

 

[Diploman]

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

 

[Diploman]

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.