The 150cc class is becoming increasingly popular in Japan, thanks to a character that is compact and easier to handle than the 250cc class, and can also be ridden on motorways, despite having a vehicle size equivalent to 125cc. Although Yamaha has a road sports model, the YZF-R15, there has been a void in off-road bikes since the production of the Serow250 was discontinued, but there is an attractive model for the overseas market, the WR155R.
Yoshimura Japan took note of this and developed the full exhaust type machine tune GP-MAGNUM Cyclone EXPORT SPEC. Here we present Constructor Yoshimura's latest muffler impressions and installation procedure.
Full exhaust for public road use with improved peak power and increased torque for city riding.
The 150cc class, a major player in Asian countries, has enough momentum in scooters, road, and off-road models to make the 250cc class, which has long been the mainstay of the light motorcycle class in the Japanese domestic market, hazy.
Against this backdrop, the Yamaha WR155R is one of the hot models expected to be introduced in Japan. Yamaha's line-up for the Japanese market includes a variety of road sports models ranging from 125cc to 1000cc, but no off-road models are officially sold in Japan, with the last being the Cerro 250, which will be discontinued in 2020, so the WR155R is being sold in the Japanese market as an imported model.
Although manufactured in Indonesia, the engine, chassis and various equipment do not give the impression of a low-cost version of the former Asian models. Rather, it has been developed with a much larger market than Japan in mind, and the average rider will have no major complaints about its basic performance, either in the city or on forest roads.
One of the few weak points of the WR155R is the factory muffler. While sound deadening and emission purification performance are of course important for a muffler, the appearance is also important to satisfy the user's desire to own a vehicle. The steel OEM exhaust with the silencer laid out on the left side of the chassis is not a quality product, although there are no complaints in terms of performance.
Several brands have released replacement exhausts for the WR155R, but because the main market is overseas, until now there have been no products for Japanese public roads. The Yoshimura Kikaikyoku GP-MAGNUM Cyclone EXPORTSPEC, released in this situation, is a highly satisfactory muffler in terms of quality as a part, as well as engine performance improvement, using over half a century of engine tuning know-how.
The Yoshimura Kikaikyoku GP-MAGNUM Cyclone EXPORTSPEC is a three-piece construction consisting of an exhaust pipe, tail pipe, and silencer. The silencer body is available with a satin finish cover as shown in the image, a polished stainless steel cover or a titanium blue cover with a beautiful burnt colour.
The catalyst is catalyzed in the middle of the exhaust pipe. The multi-stage shape of the exhaust pipe gradually increases in diameter from the exhaust pipe to the rear of the tailpipe.
The OEM exhaust pipe is made of steel and is bent with a small radius towards the catalyst located on the left side of the cylinder. The pipe in the catalyst area has to be straight, which is why it is shaped like this.
As the Yoshimura catalyst is located in the middle of the exhaust pipe, the shape of the exhaust pipe is flexible. The curve from the exhaust port to the left side of the cylinder is beautiful and does not protrude too much (note the position of the left side flywheel cover), so no protector is needed.
A two-piece protector is bolted to the silencer section of the OEM exhaust, taking into account the body design. As well as being practical, they are very plastic-like and do not have a high-quality feel.
The satin-finish-covered silencer body is matt and the riveted Yoshimura emblem is of high quality. The lines and clearances with the side covers and rear wings (the fitted vehicle has been replaced with an external wing race kit) are exquisite.
The pulsing exhaust sound and high-rpm extension are breathtaking!
The stainless steel exhaust pipe has a larger pipe diameter than the OEM steel one, and its design bent in a larger radius, gives it a simple yet powerful appearance.
On the other hand, the round silencer, available in stainless steel or titanium body, is a GP-MAGNUM type with straight exhaust and is an effective point of appeal against the stock silencer.
The exhaust has also been developed as a catalyzed specification with a catalyst built into the middle of the exhaust pipe and has been commercialized as a government-certified muffler that also complies with noise regulations.
In terms of sound, the Yoshimura Cyclone is characterized by an exhaust sound with the pulse of a single, thanks in part to the GP-Magnum silencer with its straight structure.
The clear, single-like pulse is different from a mere blast and gives a statement that is typical of a custom vehicle.
As a government-certified exhaust, both the near exhaust noise level of 92 dB and the acceleration noise level of 82 dB meet the noise regulation values, but it has a crispness that exceeds that of the genuine product from the low rpm range, and there are indeed occasions when you feel you need to be considerate of your surroundings when riding in residential areas at night.
On the other hand, as evidenced by the power and torque that exceeded the OEM engine at under 5000 rpm and at 8500 rpm during development, the engine is powerful and rises sharply when accelerating with the clutch engaged when starting in first gear.
Furthermore, the WR155R's characteristic variable valve timing switches at higher rpms, so you can feel the power increase even more.
It is the review of the long-established Yoshimura exhaust that combines the attractive sound of an aftermarket product with a solid increase in engine performance.
The clear pulse sound of the single engine, without being grating on the ears, is the result of Yoshimura's technical expertise in exhaust development. The layout and bending of the pipes leading from the exhaust to the silencer are also beautiful.
Can be replaced using only common hand tools.High accuracy is expected from Yoshimura.
The machine tune GP-MAGNUM CYCLONE EXPORTSPEC can be bolted on with standard hand tools. As the exhaust is attached on the left side, it is easier to work with it upright on a maintenance stand or similar than on a side stand where the vehicle body tilts to the left.
To remove the tailpipe fixing bolt, remove the frame protector covering the bolt.
Loosen the bolts on the clamp between the exhaust pipe and the tailpipe and remove the silencer and tailpipe fixing bolts, then pull the silencer to the rear of the vehicle.
The tailpipe and silencer of the OEM exhaust are one piece.
Remove the clamp at the front end of the tailpipe as it will be reused on the Yoshimura exhaust. The cylindrical gasket inserted inside the tailpipe is often damaged when pulling it out, so replace it with a new one.
Remove the exhaust nut from the cylinder head section and remove the exhaust pipe. The exhaust nut can be removed smoothly using a socket spanner fitted with an extension bar.
The Yoshimura exhaust pipe is larger in diameter than the OEM exhaust pipe and has a beautifully curved shape. The protector bolted to the OEM exhaust pipe also serves the purpose of blocking the heat from the catalyst placed inside.
The exhaust gasket (right) and tailpipe gasket (left) prevent exhaust leaks by collapsing when the bolts and nuts are tightened during assembly. Once crushed, they must be replaced with new ones when attaching or detaching the muffler, as re-use can cause airtightness to deteriorate and exhaust leaks to occur.
Temporarily fix the exhaust pipe, taking care that the exhaust gasket does not fall off. A trick not mentioned in the manual is to apply a liquid gasket to the exhaust gasket before setting it on the cylinder head to prevent it from falling off.
Insert a new gasket in the tailpipe.
The tailpipe clamp removed from the OEM muffler is set so that the fingernail part indicated by the finger is in contact before inserting it into the exhaust pipe.
The tailpipe fixing bolts are re-used from OEM parts, while the nuts on the back side of the bracket are supplied with Yoshimura Exhaust. The bolts should be temporarily fastened at this stage.
The grommet rubber and collar are fitted to the silencer stay, which is temporarily fixed to the silencer. The bracket riveted to the silencer is also stamped with the Yoshimura logo.
Insert the silencer with silencer stay etc. into the tailpipe. At this stage, the position of the silencer bolt is perfectly aligned with the nut position on the seat rail side.
This precision is Yoshimura's quality.
While setting the supplied spacer collar between the silencer stay and the seat rail, temporarily fix the silencer with the supplied cap bolts.
An exhaust spring with the Yoshimura logo connects the tailpipe to the silencer. A special hook for hanging the spring is also included.
Before tightening the bolts and nuts on each part, check that the exhaust pipe and silencer are not interfering with the vehicle body. The fitted vehicle was close to the rear turn signals and navar plate due to its fenderless specification, but did not come into contact with them.
Tighten the exhaust nut, tail pipe bolt, and silencer bolt in this order from the front of the vehicle. Tighten the tailpipe bolt while holding the nut on the stay side with a spanner.
Degrease and clean the engine with parts cleaner before starting, as starting the engine with oil that has adhered during the installation process can cause staining and burning.
The engine is driven in actual operation after checking that there are no exhaust leaks from any part of the engine while idling. As the engine rpm rises, it is a great attraction to feel more powerful than the OEM one.
