An important bike for KTM in a highly competitive middleweight market
Story by Alan Cathcart
Photos by: Sebas Romero and Marco Campelli
KTM has made a key roll of the dice with the introduction of the 790 Duke, its first-ever parallel-twin powered by the all-new LC8c (liquid-cooled, eight-valve compact) engine.
Previously, KTM had only its 690 Duke single-cylinder niche model to compete in the significant segment that is the middleweight marketplace. Now, with the 790 Duke twin – aka “the Scalpel,” on account of its focused design and pared-to-the-minimum weight and bulk – KTM has a mainstream contender for marketplace supremacy, making this a vastly important bike for the company that’s both competitively priced and highly distinctive. What’s more, in transferring production of this and all other future middleweight KTM – and Husqvarna – models powered by the LC8c engine to China in 2020, KTM president Stefan Pierer will ensure that the 790 Duke, its forthcoming 790 Adventure due in a year’s time, and other later models will all be even more affordable.
With its typically sharp-edged styling by Kiska Design, the 790 Duke fills the gap between the 690 Duke single and 1290 Super Duke V-twins in the Austrian firm’s streetbike range, and in doing so brings an entirely new level of electronic sophistication to the middleweight sector, with features that some Japanese one-litre sport bikes don’t even have. Delivering a maximum power of 105 hp at 9,000 rpm with a dry weight of just 169 kg, it’s a typical KTM in terms of adding performance via reduced kilos. And in addition to a comprehensive and easily readable TFT dash and two-way quick shifter as standard, it features electronics previously seen only on bigger bikes, including inertial measuring unit-controlled traction control and cornering ABS.
A Serious Investment
Company engineers began creating the LC8c motor back in 2012; since then, the 250 people engaged with the project in research and development invested more than 111,000 man-hours (okay, several woman-hours, too), with 60 of them working full time on it, covering 604,800 km of intensive dyno testing and over 900,000 km on the open road. KTM doesn’t do things by halves, but even so, the fact that they invested so much time and money in getting this platform right indicates how important the project is to the company’s future growth strategy.
First, though, they spent two years considering whether to produce a downsized middleweight version of their larger capacity 75-degree V-twin family of engines, before settling on a DOHC eight-valve parallel-twin. “We had to get this right because it will be such an important platform for us for many years to come,” says Torsten Gaul, the Austrian firm’s head of engine R&D. Gaul says that after evaluating the two formats, it became clear the V-twin configuration would not be suitable, given he says their “main goal was to get the engine as compact as possible. With the V-twin, you have limitations regarding the seat height, because the rear cylinder sticks up into the seating area, and the engine is also longer, which means you must have a shorter swingarm for the same wheelbase, whereas we wanted a longer one for better grip. Also, the height of the engine with the throttle bodies between the vee also brings disadvantages for packaging reasons, so we decided to go with the parallel-twin format.”
Intuitive and Agile
KTM paid special attention to keeping the 88 x 65.7 mm, 799 cc engine not only light, but also narrow to help maximize cornering clearance, as well as to suit riders of all heights. “We wanted to make a bike that’s intuitive to ride, that’s light and responsive with the extra performance of a twin, but without sacrificing the agility of a single,” says Adriaan Sinke, LC8c product marketing manager. Also key was the fact that it centralizes the mass of the engine, enabling the engineers to design a more compact, easier-handling motorcycle. Plus, to be in line with the firm’s “ready to race” philosophy, they wanted to establish a visual link with their motocross bikes. Consequently, the parallel-twin concept won out.
The result is a lightweight, liquid-
cooled engine with its crankpins offset by 75 degrees with 435-degree firing intervals to replicate the gritty sound of a KTM V-twin’s irregular firing order, fitted with twin counterbalancers to eliminate vibration – one at the front of the engine and one in the cylinder head. Thus, the LC8c engine can be employed as a stressed member of the frame, which in KTM tradition is made from tubular steel, with a die-cast aluminum rear sub-frame and an “inside-out” swingarm operating the non-adjustable (except for spring preload) direct-action cantilever WP shock giving 150 mm of travel, matched up front by a 43 mm upside-down WP fork that’s equally devoid of adjustment, but gives 140 mm of travel.
Responsive and Compact Engine
The LC8c is tuned as much for mid-range torque as top-end power, peaking with 63 ft-lb at a relatively high 8,000 rpm for a parallel-twin, but there’s a broad spread throughout the rev range, with more than 59 ft-lb available at 6,000 rpm. The chain drive to the cams is offset to the right of the cylinders, while the six-speed gearbox allows clutchless quick shifting both up and down the well-chosen ratios, and is matched to a power-assisted slipper oil-bath clutch, which is cable-operated for easy maintenance and to save weight. The entire very compact engine weighs just 50 kg without throttle bodies or oil (53 kg with those included), Gaul says, compared with 41 kg for the 690 Duke’s single-cylinder powerplant on the same basis.
That’s pretty amazing for an 800 cc twin-cylinder engine, and you definitely feel the result when riding the bike. After being honoured with a brief getting-to-know-you ride last September on the prototype 790 Duke, the chance to spend a whole day on the grippy roads of Gran Canaria, Canary Islands, including a couple of hours riding the island’s Maspalomas circuit, allowed for a more intensive evaluation. As with the first time around, the 790 Duke felt small, slim, short and sporty, with a close-coupled riding stance that has your chin seemingly over the front wheel. It’s a responsive, eager-revving bike that’s not only thoroughly practical, but also hugely entertaining, and…