Engine Tuning Techniques: KAWASAKI ZRX1200/R Custom by TG NAKAGAWA
TG NAKAGAWA's ZRX1200/R
The ZRX series began with the ZRX1100 in 1997 and continued until the ZRX1200DAEG Final Edition in 2016. This ZRX1200R was built by Trading Garage Nakagawa (TG Nakagawa) based on the concept of "The stock look, but with a solid build inside." TG Nakagawa has developed many engine tuning menus for the GPZ900R series over the past 30 years since the opening of the shop. These menus can be applied to the ZRX as well since it has the same type of engine. Furthermore, they are designed to allow for high output while still being able to run smoothly for over 40,000 to 50,000 kilometers without damage. Then, the original surface treatment called R-Shot#M, which enhances the surface hardness and lubricity of the target object and extends its lifespan while also improving dimensional stability, is applied. For this bike, the treated cylinder was combined with a lightweight processed ZZR1200 stock piston to achieve high compression at φ79 x 59.4mm with a displacement of 1164cc, equivalent to the stock displacement. The other internal parts are also based on stock, and full R-Shot#M is applied to every moving part, including the pistons, piston pins, cam holders, valves, transmission, crank metal, and oil pump. Also, a TG Nakagawa ignition coil DIS (Direct Ignition System, which integrates the ignition coil and plug caps like modern motorcycles) and HIR (Hyper Ignition Reader, an ignition unit that allows the user to personalize the ignition map) are added to the system. The owner had an FCR φ39mm carburetor for this engine, but the stock CVK36 carburetor made it run very smoothly. The response is so high that the owner says, "This is good enough, I would have been a bit nervous with the FCR." This is an example of how the potential of the engine can be maximized and adjusted on the intake side, and it can be said that a new stage of engine tuning has been seen.
On the other hand, this bike also serves as an example of how to build a chassis for such a tuned engine. "We have reinforced what we consider to be weak points on the body of the ZRX series. The removable right down tube was replaced from aluminum to chromoly steel. The rear shock upper mount was reinforced and then connected to the left and right sides. Reinforcement is also added under the neck of the main frame and on the inside of the back (above the back of the carb). The front and rear axle shafts and pivot shafts are chromoly. The cowl is now frame-mounted and moved as close to the front fork as possible, and we made the brackets so that the line at the rear of the cowl is parallel to the fork. This body is quite solid and riders who run TOT (Taste of Tsukuba) say they can ride it with confidence." This method, which is based on a lot of experience, such as putting a 150 hp spec engine on a stock DAEG chassis, is one example of body tuning for the ZRX. This ZRX1200R is a bit smaller than the stock ZRX1200R, and its lightweight FRP exterior and aluminum fuel tank make it feel as light and compact as a 2020s mid-size model. With such a lightweight and solid body and a TG Nakagawa-tuned engine, the owner's words make sense. This bike is a true "modern version ZRX". It's the kind of package you want to aim for.
Handle
The handlebar is an Active Low Type, mounted on a Wheelie Street Evo Monoblock Stem (30mm offset), and the left and right master cylinders are Gale Speed VRC, which also enhance control. The gauges are stock units that are frame-mounted, just like the cowl. The mirrors are Magical Racing NK-1 Mirror Type-4, and the footpegs are by Striker.
Bodyworks
With the aim of enhancing the content while maintaining a stock look as much as possible, the bikini cowl and seat cowl are made in FRP (fiber-reinforced plastic) by tracing the stock shape. The bikini cowl is frame-mounted using original pipe brackets. The rear line of the cowl is kept parallel to the front fork, and the cowl itself is brought as close to the tank as possible (to minimize the common gap tendency in this model). The emphasis is on a good look without protruding forward and without putting weight on the handlebar.
The single-seat style seat is a TGN original seat that has been produced for 20 years and has earned a good reputation. The fuel tank is made of aluminum, also traced from the stock shape, and painted in the stock color. With these exterior weight reductions, the body of the vehicle looks and feels more compact than the stock body.
The frame itself is welded together with a bar connecting the inner left and right sides of the upper rear shock mounts (center of photo), and the front side of the bar (the two triangular shaped places seen on either side of the bar) is reinforced. This is a good idea when installing a tuned engine.
Engine
The engine is a φ79 x 59.4mm, 1164cc spec, which seems stock in terms of numbers, but it is a stock ZZR1200 engine with higher compression than the ZRX, and lightweight modifications were made to it. The pistons, piston pins, cam holders, valves, transmission, crank metal, oil pump, and other moving parts are all treated with TG Nakagawa's R-Shot#M. Additionally, there is a component welded under the neck of the frame body, and a triangular plate is welded to reinforce the area where the frame curves behind the carb. The stock aluminum right-side down tube is replaced with a Wheelie Chromoly to strengthen it.
The carburetor is currently a stock CVK36 + K-TRIC, which is more than enough to smoothly enjoy the power and response. Ignition is TGN's DIS (Direct Ignition System), which integrates the coil and spark plug holder as in modern bikes, and the TGN HIR (Hyper Ignition Reader) ignition unit.
Intake & Exhaust
The exhaust system with a full titanium 4-1 configuration and spiral collector is equipped with a special DLC (Diamond-Like Coating) silencer, customized by Nojima Engineering in collaboration with TG Nakagawa. This setup reflects the owner's particular preferences.
Chassis
The ZRX series utilizes parts with the highest-class specifications for naked bikes, such as φ43mm front forks and front φ25mm/rear φ20mm axles. However, for more upgrades, this bike uses Ohlins RWU forks and chromoly axle shafts. The front brakes consist of Brembo axial CNC4P Calipers paired with Sunstar Works Expand Discs.
The rear brakes are Brembo CNC 2P Caliper + Stock Disc. The rear axle is chromoly and the swingarm pivot shaft (φ20mm) is also chromoly. The wheels are Gale Speed Type-E in 3.50-17/6.00-17 sizes, with Bridgestone S22 tires 120/70ZR17 front and 190/55ZR17 rear.
The rear suspension features a combination of Ohlins Legend Twin Rear Shocks and a Wheelie BIG 7N01 Swingarm. The rear frame reinforcement, including reinforced shock upper mounts and left-right connections, enhances the benefits of the modified suspension and lightweight wheels. The rear sprocket is RK's H.C.S Premium Sprocket 01PS, and the drive chain has been converted to 520.
Gallery
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Specifications
About TG NAKAGAWA
TG NAKAGAWA is a cusom builder that deals GPZ and ZRX dedicatedly. They deal many complete cusotom and sell many dedicated parts. A rider hoping for further potential up to one's favorite vehicle is unmissable.
Original Source of this Article
Heritage & Legends
editor
Hakuyo
A foreigner who rides in Japan, Japanese call this "Gaijin Rider". Third year in the Webike global team. He feels and shares the real bike life in Japan then presents you how interesting Japanese customs are.
