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Class4 Engineering Established Modern Style with Distinct US Taste: Z1000R Custom

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 7 min read

Class4 Engineering's Z1000R


Class4 Engineering has been active in Yokohama since its opening in 1988. Their custom motorcycles, known as "Yokohama-Style," feature abundant use of imported American-made parts. These machines are reminiscent of American drag racing and AMA Superbikes. Prominent features include raised tails and fender eliminators that emphasize the style, which became a classic trend popularized by Class4 Engineering at the time. This modified Z1000R, created around 1993, exemplifies that style. It is based on the 1982 model R1, with an engine that has been increased to 1135cc using Wiseco pistons, incorporating drag racing know-how.


The technique of combining oil-cooled GSX-R series wheels, large-diameter front forks, and a high-strength aluminum swingarm became firmly established as a common style in street customizations. Additionally, numerous drag racing techniques are applied to the motorcycle, such as using an outboard bearing support to accommodate the wide rear wheel offset and reinforcing the engine mount. Of course the wide rear wheel, which was a prominent feature of the air-cooled Z series of the time, aims to evoke the image of a drag racer. However, what Class4 Engineering advocated was not merely a replica of a drag machine specialized in straight-line acceleration. It was a street custom with a wide rear tire and American-style colors that also made cornering enjoyable. This bike's theme revolved around that concept, and the ability to handle the high power of a drag machine served as its foundation.



The meter is stock. To create an upright posture, the handlebar is largely bent towards the rider's body.


High throttle is installed due to the change in carburetor. The throttle case is painted in the same color scheme as the bike.

Intake & Exhaust


The carburetor is a MIKUNI RS Φ36mm that has flat valves. The engine was increased to 1135cc using Wiseco Φ74mm pistons. The compression ratio has also been changed from 9:2 to 11:1. The camshaft is made by Mega Cycle, and the Serck Speed 13-row 9-inch oil cooler used to be popular in the Z1000R's era. The fuel tube is on the right side.



Rearsets are set further back than the stock. The handlebar and these rearsets contribute to a great riding position. The drive sprocket is covered to hide the 15mm offset due to the wider wheel.


SHOWA Φ43mm front forks are mounted using an '89 GSX-R1100 stem. The front brake consists of Class4 Engineering's original Φ320mm rotor and NISSIN 4 piston caliper. The wheels are GSX-R1100 (3.50-17 / 5.50-17).


Kruger&Junginger's aluminum swingarm and SHOWA rear shocks. The rear brake system also consists of GSX-R1100 parts. The exhaust system is KERKER 4-1 Megaphone, which matches the US Style.


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Part Details
Engine WISECO Φ74mm Big Bore Piston Kit
Carb / Intake MIKUNI RS36 Carburetor Import Product
Exhaust KERKER B2194 MG Exhaust
Frame Kruger&Junginger Aluminium Swingarm
Brake CLASS FOUR Original Φ320mm Rotor
Suspension ADVANTAGE SHOWA RS Rear Suspension (Hydraulic Initial Adjuster)
Handle / Steering CLASS FOUR Original Super Bike Bar
NHK Steering Damper ODM-3160
Oil Cooler SERCK SPEED 9 inches 11 Low Oil Cooler

About Class4 Engineering

The price of the billet parts handled by Class4 Engineering are reasonable, and you can readily customize your beloved motorcycle. Their stylish parts are popular among Japanese fans as well as its homeland fans.


Class4 Engineering brand page

Original Source of this Article

Heritage & Legends




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.