[CDN Duke]

has anyone tried this on the duke 390 ?

https://www.youtube.com/watch?v=TAk1ABgcO04&app=desktop

How does the hole cut in this video match up with the structure in the 390 mufflers that have been dissected?

It actually sounds decent to me and with Akra map, maybe there won't be too many negatives?

 

[CDN Duke]

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.

 

[CDN Duke]

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.