Back in the era of my misspent youth, things used to be so much simpler. You’d take your new motorcycle home, bolt-on a “Closed Course Only” aftermarket exhaust, and (if you were smart) install a jet kit in the carburetors. The result was significant power gains and weight loss. Today, things are a little more complicated. Carburetor jet kits are illegal in some states, and the OEMs are making it tougher for EFI piggyback systems to alter what the EPA dictates your air/fuel tuning should be. Additionally, it is much more difficult to get aftermarket exhausts in some places.
While exhaust manufacturers have responded by building EPA-legal slip-ons that meet noise restrictions, the result is the limiting of easy power gains. My experience with the Akropovič “Slip-On Line” ($860) from the KTM PowerParts catalog highlights this challenge. After the slip-on was bolted in place, a trip to the dyno revealed the sad news: a 0.8 peak horsepower loss. While the muffler, IMO, looked and sounded better (not to mention the 2.1 lb. weight savings), some MOrons mocked me for my folly. At that moment, I vowed to increase the power output of my KTM 790 Duke.
Because I was out of my league with this challenge, I reached out to KTM guru and head honcho at Rottweiler Performance, Chris Parker, to see if he could help me with my challenge. While on the scale of products/services that Rottweiler provides, my request is relatively small. After all, Rottweiler builds adventure bikes capable of finishing fourth in the six-day Sonora Rally Against purebred race bikes. My requirements were simple: no excess noise (i.e. I was keeping my slip-on legal), no reduction in streetable rideability, and no Check Engine light (a common side effect of circumventing an EFI system’s anti-tampering features by disconnecting O2 sensors).
During my initial conversation, Parker said that he would free up the intake and adjust the tuning within the EFI’s restrictions to achieve my goal. I just needed for him to finish developing his new intake kit, the Power Plate, before we could proceed.
Rottweiler’s Power Plate replaces the solid cover of the airbox with one that has a large opening. Because this opening is behind the air filter (which remains in use), some means of cleaning the incoming air had to be incorporated. For that, Parker turned to oiled foam filter material, like that used on many dirt bike intakes. The final kit includes the plate and three different filters, one for street use and two for race applications. Installation is as easy as oiling and installing the filter, then bolting the Power Plate to the airbox. Total time was just 10 minutes.
To get the most out of this intake change, the fueling needs to be adjusted to match the exhaust being run. That poses its own set of challenges.
Before we dive into the review of the Power Commander V, we need to establish what closed loop and open loop portions of the EFI are. In its most basic sense, the closed loop is a table with one axis being the rpm range and the other the throttle positions at which the end-user has no control over the air/fuel ratio. These are dictated by the combination of the ECU and the O2 sensors in order to achieve the mandated emissions standards. Unfortunately, the ideal air/fuel ratio for emissions is not the same as for maximum power output. The good news is that in the open loop portion of the rpm range the ECU surrenders its control, giving tuners free range over the mixture to find more hidden horses.
For those interested in making the maximum power available (read racers), the ECU’s iron fist can be circumvented by disconnecting the O2 sensors and using a Power Commander to control the entire EFI table, but that leads to the aforementioned Check Engine light – or worse, limp home mode on some bikes. And the bad news is that with each new model year, the clamp on tuning gets tighter. Never fear though, the tuners have an active cat-and-mouse game with the OEMs to wrest the best performance possible out of a motorcycle’s engine.
If you’ve been riding for any length of time, you’re probably already familiar with Dynojet and its ubiquitous piggyback EFI tuner, the Power Commander V. While many riders think that, on bikes, like the 790 Duke, which have a large closed loop section of the rpm/throttle range, the Power Commander won’t do anything until the open loop is reached, they’re forgetting that the PCV also controls ignition timing.
Parker used this trick with his maps for the PCV on the LC8c engine. Then he optimized the air/fuel ratio to ease the transition from closed loop to open loop on up to redline. The result is the power that riders like me are looking for: more power with no error message (since the O2 sensors are still doing their job in the range that the EPA has total control of).
Installing a Power Commander V is pretty straightforward. While you’ve got to be an accomplished enough mechanic to gain access to the fuel injectors and the ignition coils, the actual installation is a simple model-specific plug-and-play. You may have to use a Posi-Tap or two, but typically, no wires need to be cut. The most common challenge people face is mixing up wire color combinations. A red/yellow wire is different from a yellow/red one.
After 90 minutes of wrenching, I thumbed the starter, and the 790 burst to life. The next morning, I was off to the dyno for verification. The dyno numbers were clear, and at every engine speed above 4,200 rpm, the LC8c made more power. Most importantly, the dip in the midrange was almost completely gone. However…
In a symptom that neither Dynojet nor Rottweiler could initially explain, the engine fell on its face from 3,000-4,200 rpm. It was awful. Much troubleshooting ensued, and Dynojet’s tech support was extremely helpful. The decision was ultimately made to make a warranty replacement of the PCV. I copied the Rottweiler maps to my PC and waited for the new unit.
And the same thing happened again.
Because he is a generous soul (and he likes a challenge), Parker offered to troubleshoot my bike, and honestly, at this point, I was hoping that I’d done something stupid in my installation. Well, the bike did the same thing on Rottweiler’s dyno as it had done on the MotoGP Werks’ one we do the bulk of our MO testing on. So, out of curiosity, Parker pulled a Power Commander from his inventory and installed it.
And it worked like a charm.
I can’t say how freaky it is to get two faulty units in one product review (I even checked serial numbers to make sure that I hadn’t had the first one returned to me by accident), and Parker says that, out of the thousands of Power Commanders he’s sold, his returns have been in the single digits.
With the Power Commander finally working, the next step was to get a baseline run with the stock airbox and no map on the PC. We then ran the Rottweiler street map along with the Power Plate. While I expected the combination of the freer breathing airbox and the ability to control the fueling to deliver an improvement in the top end, I was surprised to see the bulk of the effect in the midrange, which showed improvement from 4,000-7,000 rpm, with the biggest gain at 5,400 rpm, where the increase was 3.5 hp or 7%. The torque saw a similar gain of 3.3 lb-ft. but 1,100 rpm sooner. The modified system delivers increased power throughout the entire rev range, with the exception of a couple of hundred rpm between 7,000 rpm and 8,000 rpm. Peak power is only up by a negligible 0.9 hp to 96.0 hp. Although the power curve isn’t completely straight, the primary effect of this modification was to negate the soft spot in the midrange while slightly improving power everywhere else.
When riding the 790 with the Rottweiler map and Power Plate in place (even while troubleshooting the Power Commander issue), I was impressed by how the midrange felt tighter and more responsive – although I have to admit that the placebo effect (and perhaps the additional growl coming from the airbox) had me believing that the peak power was improved, too. Dynos don’t lie, and the Rottweiler dyno showed that I got the change that I was seeking in the midrange. A 7% gain is pretty good for a modern EFI/ECU system and its myriad of constraints on a tuner – particularly while maintaining street-legal sound output. There’s even more power available for riders who are willing to mount a louder, freer breathing race system and run with the check engine light on constantly, but I’m unwilling to do either. My 790 is a street bike first, and I like my neighbors.
So now, as I roll on the throttle exiting the corners of my favorite winding road, my smile is even bigger. Fueling is hiccup-free, and the engine feels more spritely as it rips from 5,000 rpm up to my next shift point. Even with the challenges I had along the way, this pair of modifications is, I believe, worth the cost. The Dynojet Power Commander V retails for $420, and if you buy it from Rottweiler Performance, you get the maps and any future upgrades to them for free. The Power Plate costs $100 and probably holds even more potential when paired with a less restrictive exhaust than I am willing to run.
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