Join Date: Apr 2015
Location: Murrysville, PA, USA. A pleasant, wooded suburb of Pittsburgh.
The preceding comments by LNICK and Mikebet - two guys with many years, many bikes, many miles/kms on their moto resumes - largely reflect my views on the question of hot-rodding the 390 engine for more power/torque.
Certainly, it is possible to extract more power from the motor: Many competition-minded RC owners do extensive (and expensive) modding to make their bikes faster; a Full-Monty engine makeover from Chad Wells, plus a carefully-mapped fuel controller, airbox mods and high performance air filter, along with one of the (few of many) aftermarket exhausts that can actually make fractionally more power than the stocker - all of this can reportedly raise output to the vicinity of 50 HP, along with increased torque. The total bill will set you back somewhere in the neighborhood of $3k. For 7-8 additional peak horsepower and better mid-ran ge torque. For some, this investment is entirely worth the cost. On the Duke side, there are a few who go for the full power upgrade, but most focus more on smoothing out power delivery, seeking to eliminate the low-range power roughness that many perceive as a product of the lean factory fuel mapping. Whatever the degree of power enhancement, the per-HP cost is high.
To my mind, the KTM engineers did an admirable job of designing a sub-400cc motor that delivers class-leading power. The bike is satisfyingly quick and fast for this category - If more power and speed is required, it is far more cost-effective to simply buy a bigger, faster bike. I have studiously kept my engine completely stock: motor, intake, air filter and exhaust are as delivered. It starts, idles, runs well throughout its power range, never stalls and overall is a very entertaining (and to date, entirely reliable) little powerplant. Does its job. Delivers a consistent 61-63 Miles per US gallon. It's not perfect - could be smoother, but it's a single - but I am happy. KTM's engineers did an excellent job, and I don't feel particularly compelled to second-guess them.
I like this little engine so much, in fact, that I want it to last a long time. Any mods I would do to the engine/intake/exhaust system would be in the interest of reducing thermal/dynamic stress and prolonging engine life. The engine is already mapped, for emissions purposes, with a borderline lean AFR: In addition, its per-liter power output is phenomenal, and would cost a fortune to replicate in an automobile. This is where a fuel controller may eventually come into the picture for me: I can see the logic in reducing the engine's thermal stress by enrichening the AFR. A little fatter mid-range torque curve as a by-product would not be unwelcome, but I am wary of significantly increasing the peak power output of an engine already so potent from the factory. My principal objective is cooler running.
One of the most entertaining aspects of owning a Duke is that - as capable as the bike already is as delivered - it is endlessly amenable to modifications of every sort. For me, modding the bike has been almost as much fun as riding it. I don't begrudge anyone who wants to modify the bike's engine/intake/exhaust system. I just don't feel the need, and I think seeking more power from this mill has a very questionable cost/benefit ratio: big bucks for small gains.
When you are a card-carrying old fart like me, you have the privilege of being annoyingly opinionated. As Mikebet puts it, I should not be taken seriously.
"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