The arrival of the Kawasaki Ninja ZX-4RR in the summer of 2023 heralded one of the most exciting new models of the last several years. Throwing a curve ball into the modern-day sport bike market, the bike featured a liquid-cooled inline four-cylinder 399 cc engine, which immediately became a viral topic of discussion amongst track day enthusiasts and road racers alike.
Inside Motorcycles original test of the ZX-4RR in 2023 saw this reviewer falling head over heels and proclaiming it as a home run on the part of Kawasaki, thanks in large part to the inclusion of top shelf features such as dual disc front brakes, traction control, selectable power modes, an up/down quick shifter and slipper/assist clutch with auto blip.
Click here to read IM’s original review of the Kawasaki Ninja ZX-4RR.
While the ZX-4RR is an amazing track-ready motorcycle right out of the box, admittedly, there were some items holding it back from being a full-on grand slam home run (apologies for all the baseball analogies, but as I write this, game 4 of the World Series is playing out on the television in front of me). Topping this list would be the status of the of the engine when it arrives at the dealership.
Thanks to the reality of emissions/noise requirements, the ZX-4RR has been essentially neutered for the North American market. While horsepower or torque specifications were not available for the Canadian model, our initial track test left no doubt that real numbers were well below the 75 horsepower and nearly 28 ft-lb of torque that Kawasaki advertises in markets that are not subject to the same regulatory restrictions.
Despite this shortcoming, the Ninja ZX-4RR has proven to be a great success for Kawasaki with customers lining up to purchase this unique sport bike. Among those who were lucky enough to purchase one in the first year, was my track day colleague, Claude Bergeron. Anxious to unlock the full potential of his new motorcycle, Claude’s first stop was at Redline Motorsports Calgary where it was fitted with a Graves Performance slip on exhaust along with an ECU flash and some quality time on Redline’s in house dyno.
Conversation with Redline head honcho James Carlin revealed that while it sounds great (more on that in moment) the Graves slip on had minimal impact on the engine’s output with the real win coming from the ECU flash. As depicted in this graph where the green lines are the fully stock, blue is with just the Graves Performance slip on and Red is the Graves with full ECU flash and dyno tuning, the ECU flash provides a dramatic increase in performance, completely eliminating the dead zone that we discovered in our original test when pushed beyond 12,000 rpm.
With the flash complete, Claude’s ZX-4RR continues to produce power well past 14,000 rpm, leaving me envious and wishing for a chance to take this newly uncorked model for a test ride. Well, sometimes wishes do come true and this fall Claude was kind enough to bring his ZX-4RR to Rocky Mountain Motorsports and let me spin some laps on the same track where I did the original test.
Flipping the starter switch the first thing that catches your attention is the auditory sensation of the Graves exhaust can. Where the stock setup has a nice little growl, this aftermarket option emanates a sound that will be right at home on racing grid and subliminally induces the rider into blipping the throttle. Yes, by itself it may not provide a dramatic change in performance, but man does it ever sound good.
Out on the track with a couple of warm up laps completed, it was time to open up the ZX-4RR, and simply put it was an absolute blast. Where the stock setup loses steam around 12,000 rpm leaving you in search of the next gear, Claude’s ZX-4RR pulls hard all the way until the motor is literally screaming at you to shift. The change in the bike’s character is so dramatic that it actually catches you off guard the first couple of times that you crack the throttle wide open. There was a notable, albeit brief, dip in the powerband just beyond 9,000 rpm – the graph from the dyno run also highlights this – but with the ECU flash, the ZX-4RR’s fun zone rarely sees the bike spend anytime below 10,000 rpm so it really isn’t a factor.
With a few sessions completed, I reluctantly decided it was time to give the bike back to Claude before I changed my mind and tried to make a run for it. Sitting in our pit talking about the amazing impact of the changes Redline made to this motorcycle, it is hard to imagine anyone leaving this bike in the stock setup.
Of course, the big question for many will be the cost, which is really something where you must consider the cost of the overall package. Listed on the Canadian Kawasaki website, the Ninja ZX-4RR has an MSRP of $11,199 (2025 model pricing). Add on the cost of an ECU flash and dyno tune in the range of $700 plus another $800 or so for an aftermarket exhaust and you are starting to move into the same zip code as the MSRP for the 2025 Ninja ZX-6R ($14,099 per the Canadian Kawasaki website). This is where personal preference and intended use comes into play. Keep in mind that the real performance gain on the ZX-4RR comes from the ECU flash, so for under $12k you can have a lightweight sport bike pushing close to 70 hp at the rear wheel. For a tight technical track like Rocky Mountain Motorsports the ZX-4RR may very well be the perfect bike, and believe me when I say that it will leave you smiling for days.
A major league (sorry one last baseball reference) thank you to Claude Bergeron for the use of his amazing motorcycle as well as the team at Redline Motorsports Calgary (www.redlinecalgary.com) and Rocky Mountain Motorsports (www.rockymotorsports.com).
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