KTM 790 Duke Project: Building A 790 R

Evans Brasfield
by Evans Brasfield

One man's vision of the perfect middleweight Twin

When I initiated this project with MO’s long-term 790 Duke, my goal was simple. I just wanted an excuse to keep the bike as long as possible before I would be required to give it back to KTM. However, even before I considered buying the 790 for myself, I hatched another plan. I was going to build my vision of what a 790 Duke R would look like. Now, KTM has let the cat out of the bag and proved that a 790 Duke R really was never planned, meaning that it decided on an 890 Duke R instead. While it is beyond my capabilities to bump up the engine’s displacement (and retune the counterbalancers or shorten the shifter throw, among other things), as I run down the list of changes I applied to my 790, I don’t think that, although I was just trying to craft my conception of the ideal naked middleweight Twin, I strayed very far from where KTM has taken the 890.

Building an R

The two places where KTM cut corners on the 790 Duke are pretty much agreed upon: the brakes and suspension. Fortunately, there were several good options available to address these issues. Rather than saying these were shortcomings in the Duke, I felt these were obvious clues as to where the next iteration of the 790 was heading. After all, Triumph has been quite successful with multiple variations of its Street Triples. Why wouldn’t KTM do something similar? At least, I was half right.

In the comments of the other articles I’ve written about this project, some of the more cynical readers have approached these changes as things that I needed to fix – as if there was something inherently wrong with the Duke. I see it more as I was excited by the platform’s potential. That’s why I ended up buying the 790. The desire to sharpen the bike’s performance simply makes sense for a rider of my background, and the fun of taking on this sort of project can’t be ignored. I’ve spent many happy weekends in my garage wrenching on the 790, but the real payoff is riding the bike that I’ve created.

Adjustable Suspension

The non-adjustable OEM suspension was the 790’s Achilles’ heel. Although it offered the compliance that makes street riding more comfortable, it could find itself out of sorts at track speeds. When I made my list of upgrades for the 790, finding new suspenders for it resided at the top of the list. Unfortunately, I had to wait quite a while before I could make the change because of articles we had planned for our long-term Duke.

The preload-adjustable only stock shock was swapped for a reservoir shock that has hydraulic preload adjustment, high/low-speed compression damping, and rebound damping.

Although I shopped around, I pretty much knew that I’d end up with the WP Apex Pro components. First, KTM owns WP. So, they belong together. Then there was Chris Fillmore’s record-setting run up Pikes Peak. WP’s reputation for quality components and the fact that I’d never ridden on non-OEM versions of WP suspension before and wanted to see how it performed played an important role in my decision. Also, WP markets the Apex Pro as street-focused, and that fits for most of what I do with the bike. The full-adjustability of the suspension allows me to tune the ride for the task at hand. I have three settings that I typically use: sporty, for every day rides and canyon runs; soft, for extended freeway time; and track, which varies for each venue. I couldn’t be happier with the WP suspension.

Yes, the WP Apex Pro fork is fully adjustable for preload, compression, and rebound damping. With the stock fork, you get nothing.

The cost of the WP Apex Pro components ($879 for the Apex Pro 6500 cartridges and $1099 for the Apex Pro 6746 shock with the optional hydraulic preload adjuster) is nothing to sneeze at, and this upgrade alone put the cost of my project over the base price of the 890 Duke R – $11,699. However, according to our contacts at KTM, the 890’s suspension slots in between the 790’s and the Apex Pro. For example, the 890’s fork has no preload adjustment, and the shock, while offering full adjustability, is of a different construction.

MO Tested: WP Apex Pro 6500 Cartridges And 6746 Shock For KTM 790 Duke

Better Brakes

Brake upgrades were among the first changes I made to the bike, and I’m happy with the progression throughout the course of this project. The baby step of fitting EBC Double-H pads delivered the desired initial bite of the brakes, while the KTM PowerParts/Galfer Wave Discs improved the overall stopping power with the added benefit of significantly reducing the weight. For a while, I was satisfied with this arrangement. That is, until I rode the 2020 Triumph Street Triple RS, with its Brembo MCS master cylinder and M50 calipers. This started me thinking.

The combination of EBC Double-H pads and the KTM PowerParts Discs delivered the additional braking power I was looking for.

At this point in the project, the combination of the OEM master cylinder, the EBC pads ($80), and the PowerParts discs ($458) provided more than adequate stopping power for hauling the bike down from speed. Still, I wanted more immediate application of the front brake with less free play in the lever. While I didn’t have the budget for a full Brembo system, including M50s, I decided to try a Brembo 17 RCS Costa Corta master cylinder to see if it would get me to where I wanted to be. Long story short, the 17mm piston was too small for the piston sizes of the J.Juan calipers, and I ended up using the Brembo 19 RCS Corsa Corta ($372). Now, I have the braking power, feel, free play, and adjustability I wanted all along. However, those M50s – or maybe some Stylemas – still call to me late at night, when I’m cruising the net…

The Brembo 19 RCS Corsa Corta master cylinder provides a wide range of adjustability to suit riders’ needs. The power and feel at the lever are worth the cost.

MO Tested: KTM PowerParts Wave Brake Discs

MO Tested: Brembo 19 RCS Corsa Corta Master Cylinder

More Midrange

Don’t get me wrong, one of the 790 Duke’s strengths is its ample midrange for its displacement. That said, the more familiar I became with the LC8c engine, the more I noticed a slight softening of power in the 4,800-6,000 rpm range. I even used this dip as my around-town shift point for extra-smooth clutchless upshifts. Then, also, there was the matter of pride associated with the loss of 0.8 peak hp after installing the Akropovič “Slip-On Line” ($860) from the PowerParts catalog. (A fact that several of you MOrons roasted me for in the comments.) So naturally, I explored power upgrade options. A quest for redemption? I’ll let you decide.

The key to more midrange: Dynojet Power Commander V and Rottweiler Performance Power Plate.

In the end, I settled on a Dynojet Power Commander V ($420), a Rottweiler Performance Power Plate ($100), and Rottweiler’s Street Map (Rottweiler maps are included with purchase of a Power Commander V from them) for my exact setup (Akra slip-on with Power Plate). The initial results were promising – with an extremely large caveat.

The increase in midrange performance is visible on the dyno graph. What’s hard to see is that the torque peak has moved 1,100 rpm lower.

The good news was that, at every engine speed above 4,200 rpm, the Duke made more power. However, there was a puzzling flip side to my power modification that no one was initially able to explain. The problem was that from 3,000-4,200 rpm, at anything above 1/2 throttle, the engine fell flat on its face. Neither Dynojet nor Rottweiler have experienced this with any other 790 Duke. Long story short, the problem was caused by bad Power Commanders – yes, plural. Once a good one was swapped in, the 790 Duke put out the dyno graph shown here. The midrange received a 7% (3.5 hp) bump in power while the torque curve grew by a similar amount and had its peak come in 1,100 rpm earlier. Oh, and the Power Plate gives the engine a nice growl I can hear from the saddle without frightening the horses.

The Akropovič slip-on looks and sounds nice, but it doesn’t provide any increase in power in it’s EPA-legal form.

MO Tested: Dynojet Power Commander V And Rottweiler Performance Power Plate For KTM 790 Duke

Weight Reduction

While I could clearly stand to lose a few pounds (like 20!), I would be remiss if I didn’t mention that many of the modifications I made to the 790 Duke also shaved off excess poundage. (Some changes, like the Evotech-Performance Crash Bobbins and Front/Rear Spindle Bobbins, added weight in exchange for their crash protection.) Some upgrades, like the PowerParts Discs and the Akropovič Slip-On, shaved pounds, 2.9 lb. and 2.1 lb., respectively, while most losses were in the ounces. Still, the changes add up and make a performance difference in every riding situation. Notably, the biggest weight savings on the 790 came from installing a Full Spectrum Power Pulse IPT P10L lithium battery ($219) that subtracted 4.9 lb. I left a couple of other weight reduction items on the table, though. Removing the catalyzer saves 6.0 lb., but makes the bike too loud for my tastes (that’s without considering the legality). Swapping out the stock wheels for forged ones saves weight and rotational mass, but this mod is beyond my means, right now. In the end, the bike weighed in at 398 lb. – down from the original 411 lb. – on the official MO scale.

The Full Spectrum Power battery slots into place with a minimum of persuasion. The leads just barely fit the battery’s different bolt orientation. A nice addition to this project.

The Hard Numbers

790 Duke R Costs

WP Apex Pro 6500 Cartridges$879.00
WP Apex Pro 6746 Shock$1,099.00
AF1 Brake Line Adapter$35.00
Brembo 17mm RCS Costa Corta with Reservoir and Mirror Mount$450.00
EBC Double-H Pads (2 sets front and 1 rear)$117.00
KTM PowerParts Wave Discs$458.00
Akropovič “Slip-On Line”$860.00
Dynojet Power Commander V$420.00
Rottweiler Performance Power Plate$100.00
Full Spectrum Power Pulse IPT P10L$219.00
Performance Total:$4,637.00

The first thing you will notice is that the cost of these changes is significantly more than the price difference between the 790 Duke and the 890 Duke R (even when you add the additional cost of the Quickshifter+ and Track Mode for parity). This doesn’t surprise me since the economies of scale work in KTM’s favor. Go ahead and tease me about how I could have waited a year and just gotten an 890 Duke R. My coworkers certainly have with great enthusiasm. Still, making the bike I thought KTM should have built was never really the point. Instead, my goal was to build the naked parallel-Twin I’d always wanted, and the KTM 790 Duke turned out to be an ideal platform. I just wanted to spice it up a little. Plus, I had the pleasure of installing most of these parts myself.

Am I done with my 790 Duke Project? I think so.

Then again, the 890 Duke R’s flatter handlebar looks intriguing…

Evans Brasfield
Evans Brasfield

Like most of the best happenings in his life, Evans stumbled into his motojournalism career. While on his way to a planned life in academia, he applied for a job at a motorcycle magazine, thinking he’d get the opportunity to write some freelance articles. Instead, he was offered a full-time job in which he discovered he could actually get paid to ride other people’s motorcycles – and he’s never looked back. Over the 25 years he’s been in the motorcycle industry, Evans has written two books, 101 Sportbike Performance Projects and How to Modify Your Metric Cruiser, and has ridden just about every production motorcycle manufactured. Evans has a deep love of motorcycles and believes they are a force for good in the world.

More by Evans Brasfield

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3 of 34 comments
  • B Andy B Andy on May 23, 2020

    I recently bought one of the last "New" '18 790's left here in Australia, its my first Naked bike after riding super sports for 20 years, my question is would you consider adding Woodcraft clip-on's?

    • Evans Brasfield Evans Brasfield on May 24, 2020

      I moved the bar mounts to the forward position and rotated it slightly forward. I may add the 890 bar, but I don’t think I’ll go as far as clipons. I know of riders who have done it and are happy, though.

  • Eddie Eddie on May 27, 2020

    Love the bike! Always feel special when you build it vs just buying it. Having said that, KTM’s are good value from the factory. I can see why KTM has become the largest European manufacturer.