Riding the Difference: SUZUKI GSX1100S KATANA Custom by Custom Factory KATANAKAJI

• GSX1100S
• Katana

• Share:

• 
• 
• 

Custom Factory KATANAKAJI's GSX1100S KATANA

This KATANA, finished with a red frame and a red-and-silver SBE (1987) color scheme, features gold front forks and matching 18-inch wheels at both ends. It’s a beautifully composed machine built by Custom Factory KATANAKAJI, and the centerpiece of the custom work is the engine—an oil-cooled unit fitted in place of the original.

“The owner came to us saying he wanted to ride a KATANA with an oil-cooled engine,” explains Mr. Ishii of KATANAKAJI. “He already owns a completely stock KATANA, so this one was about experiencing the contrast—and having fun with a custom bike. At our shop, we already have data for mounting oil-cooled engines into the KATANA chassis, including engine position for optimal weight balance and component layout. Plus, we sell a dedicated engine hanger kit for installing these engines into the KATANA, so just like our previous builds, we were able to fit it without any issues.” True to its name, KATANAKAJI is a shop focused on customizing KATANAs and oil-cooled engine models—so naturally, a fusion like this is well within their capabilities.

Oil-cooled engines are more compact than the KATANA’s original engine, both front-to-back and side-to-side, and they also deliver more power in stock form. For reference, the stock KATANA engine produces 111PS, while early GSX-R1100 engines output 130PS and later versions up to 143PS.

“We built this engine using JE pistons to increase displacement to 1216cc and added a Yoshimura ST-1 camshaft, along with a close-ratio 6-speed transmission we had in-house,” Ishii continues. “It was a full overhaul with tuning included. The base is sort of a hybrid of a 1200 (like the GSF1200, with a bore and stroke of 79 x 59mm for 1156cc) and an 1100 (the early GSX-R1100 was 76 x 58mm/1052cc, later 78 x 59mm/1127cc). The top end is from the 1200, the bottom end from a late 1100, and the crankshaft is from the 1200.”

Why the 1200 crank? “Because the 1100’s cam chain tensioner guide is no longer available new, which means you can’t do a full overhaul with 1100 parts anymore. If you really want to use an 1100 engine, your only option now is to find a good used one. Also, even among oil-cooled heads, the intake and exhaust port shapes differ between 1100 and 1200, and the 1100 produces more power. So if you understand the characteristics of each component, you can change the performance traits by combining different blocks and parts. It’s flexible like that. That’s why we call it a hybrid.”

This build isn’t just a simple engine swap—it’s a carefully considered combination, accounting for parts availability and performance characteristics. Stock parts for KATANA engines are becoming harder to come by. Although oil-cooled engines face similar challenges, the ability to mix components across generations is a major plus.

The frame has been reinforced in 11 locations: the neck, the backbones, behind the carburetor (with added plates inside the curved sections), at the joints connecting both sides of the frame behind the engine, above the swingarm pivot, near the upper rear shock mounts, and more. The thicker front forks (upgraded from 37mm to 43mm) and the swingarm with a sway bar are both one-off parts fabricated by KATANAKAJI. The shop also crafted the custom battery box, rearsets, and under-seat tray for electrical components. Even the custom engine sliders fitted to the cylinder head are KATANAKAJI originals, and they can be installed on KATANA engines too.

This level of fabrication and data-backed chassis design is KATANAKAJI’s hallmark. Their approach to building oil-cooled KATANAs has been refined over more than 10 years of racing in the Hercules class of the Taste of Tsukuba (TOT) series with their in-house race machine, “KATANAKAJI KATANA.” Every lesson learned—whether about engine tuning, chassis setup, or airflow for cooling—feeds back into their custom builds. You can bet this Katana rides very differently from stock, and it would be fascinating to hear the owner’s impressions.

Handlebars

The windshield and twill-weave carbon windshield base are made by Magical Racing. The cowl lips are also carbon, and the headlight has been replaced with an LED.

The meter box housing the stock gauge is also from Magical Racing. The stem is a one-off made by KATANAKAJI. The clip-on handlebars are from BABYFACE, and both the brake and clutch master cylinders are Brembo RCS models. The fuel tank is now made of aluminum.

Bodywork

The seat is styled after the SBE color scheme, with red front and rear sections. The tail cowl is made of carbon, the rear turn signals are in the stock position, and the front turn signals have been moved next to the oil cooler.

Engine

The engine is a hybrid combining oil-cooled 1100 and 1200 components, now built to 1216cc with JE forged 81mm pistons and a 1200 crankshaft featuring a 59mm stroke. The camshaft is a Yoshimura ST-1, and the 6-speed close-ratio transmission is by KATANAKAJI. The engine sliders—with aluminum bases and Duracon slider pieces—are KATANAKAJI’s original parts. The frame has been reinforced at 11 locations: the neck, the backbones, at the left and right bases of the connecting bars, behind the carburetor, above the pivot, near the upper mounts of the rear shocks, and other points. It has been repainted in red.

The carburetor is a TMR 40mm, paired with Smooth STREAM oval-type air filters. The red filters match the red color scheme of the bike.

Intake & Exhaust

The exhaust is a Techserfu titanium 4-into-1 system. Its routing and power delivery reflect KATANAKAJI’s oil-cooled tuning expertise.

Chassis

The rearsets are custom-made by KATANAKAJI. The aluminum engine mounts, visible above and below the pivot area, allow the oil-cooled engine to fit into the KATANA frame. The front mounts are also KATANAKAJI originals.

The front forks are Ohlins RWU for the CB1300SF SP, allowing radial Brembo GP4-RS calipers to be used. The discs are SUNSTAR Custom Type.

The rear brake uses a Brembo P2-RS84 2-piston caliper and a SUNSTAR disc. The wheels are GALE SPEED Type-N, forged aluminum, in 2.75-18 front and 4.50-18 rear sizes.

The aluminum swingarm, thicker than stock with a robust rectangular cross-section and an added sway bar, is a one-off by KATANAKAJI. It’s paired with Ohlins Legend Twin rear shocks.

Gallery

Specifications

Part	Details
Engine	JE Pistons Forged Piston Kit Φ81mm YOSHIMURA ST-1 Camshaft KATANAKAJI 6-Speed Close-Ratio Transmission KATANAKAJI Engine Sliders
Carb / Intake	Yoshimura MIKUNI TMR Φ40mm Smooth STREAM Air Filter Oval Type
Exhaust	Techserfu ALL TITANIUM Exhaust TYPE-1, Solid Titanium
Frame	KATANAKAJI Aluminum Swingarm KATANAKAJI Oil-Cooled Engine Mounting Kit for GSX1100S
Brake	brembo RCS Front Brake Master Cylinder brembo GP4-RS Front Calipers SUNSTAR Custom Discs for Front & Rear brembo P2-RS84 2P Rear Caliper
Wheels	GALE SPEED [TYPE-N Front] Aluminum Forged Wheel GALE SPEED [TYPE-N Rear] Aluminum Forged Wheel
Suspension	OHLINS Upright Front Fork RWU for CB1300SF SP OHLINS Rear Suspension Legend-Twin
Drive System	D.I.D 520ZVMX Drive Chain
Handle / Steering	BABYFACE [RaceConcept] Handlebar Kit, Flat Type, Short, Offset brembo RCS Clutch Master Cylinder YOSHIMURA PRO-GRESS1 Temp/Volt Meter Magical Racing Meter Cover, Twill Weave Carbon Magical Racing Meter Box
Bodyworks	Magical Racing Windshield Base Beater Aluminum Tank
Electrical	BS BATTERY BS Lithium-Ion Battery BSLi-06

Original Source of this Article

Heritage & Legends