Join Date: Apr 2015
Location: Murrysville, PA, USA. A pleasant, wooded suburb of Pittsburgh.
If you've just received your Duke, it would seem rather premature to conclude already that the stock exhaust needs to be swapped for an aftermarket unit. You don't appear to be giving the OEM exhaust much of a chance, or any credibility. Before you rush into spending many hundreds of $ on an aftermarket exhaust, consider this: The 390's factory exhaust is a carefully-engineered, highly-tuned unit that extracts excellent HP and torque from the motor - so much so that aftermarket 390 exhaust vendors struggle to match the stock unit. If you fit many currently-available aftermarket exhausts you are likely to experience power and/or torque loss; worse, you will be changing the engine's air/fuel ratio (AFR). For emissions purposes, the 390's engine is factory-mapped very lean. Fitting an aftermarket exhaust, aftermarket air filter or modified airbox lid will alter the bike's AFR towards a hyper-lean condition that can do serious engine damage. If you really feel the need to modify these components, these AFR-sensitive changes should be done in conjunction with fitting a fuel controller that can adjust AFR to a safe level.
Downsides to the stock exhaust: It is rather heavy (includes a catalytic converter); bulky; will make the underwhelming OEM shock perform even worse by transferring heat. Advantages: Makes good power; perfectly mass-centralized; invulnerable to damage in a crash; emissions controlled; it has a civilized, fairly quiet tone; it comes FREE, included with your Duke. For the price of an aftermarket exhaust, you can fit many upgrades that are actually useful. The 390's exhaust tone seems to be a source of controversy: many owners are happy with the controlled, unobtrusive exhaust note; others crave something more raucous. A 373 mono, realistically, is hardly the ideal bike to emulate a Harley. Does a loud exhaust convey some "macho" quality? To some, perhaps, but this sort of machismo is about as functional as oversized tires - ie, not at all.
The only aftermarket exhaust currently on the market that can match the stock unit for central location and compactness is the Werkes USA unit. The Werkes' main advantage is lightweight construction, yielding a significant weight savings over the OEM piece. There is no documented evidence of power gains with the Werkes, however, but the unit is reported to be VERY loud. Lightweight and loud would at least check two of your boxes (for a handsome price). But it would still be dangerous for your engine's health to run this unit without a fuel controller.
Why not just live with the stock exhaust for a few months before you decide that it has to go? It's the most compatible thing available for your engine, works very well, and you could do many good things for your bike for the price of an aftermarket exhaust that has dubious, possibly negative, benefits. You may come to appreciate that the KTM engineers who designed the OEM exhaust are no fools.
"If you don't know where you're going, you might wind up somewhere else."
2015 390 Duke
1980 Moto Guzzi V50 II (becoming a cafe racer)
1984 Moto Guzzi SP 1000
Last edited by Diploman; 03-28-2016 at 09:06 PM.