A Real Catapult: 1300cc Suzuki GSX-R Slingshot Turbo

Pro Street 51: KOS’THOR’s Turbocharged, NOS-injected “GSX-R1300” Slingshot…  

When Suzuki introduced the original GSX-R1100 in 1986, it sent a shockwave through the motorcycling world. The boys from Hamamatsu had put an absolute unit of a 1052cc engine in their revolutionary aluminum-framed GSX-R chassis. Motorcycle reviewer and historian Roland Brown remembers: “The Suzuki GSX-R1100 was so fast, I had to recalibrate my brain.”

In 1989, the new Slingshot model replaced the original Slabside GSX-R1100, boasting a more rigid frame, more powerful 1127cc oil-cooled engine, larger “Slingshot” carbs, and more.

“For 1989, Suzuki built the bike that everyone knew it was going to build. And what a bike it is. Light, powerful, and almost sinful in purpose… The new GSX-R isn’t a race-only bike, but it’s close. That’s part of the GSX-R manifesto: to design racebikes, and then adapt them to the street…” –Cycle World

Today, these 1100 Gixxers are still revered as some of the stoutest air/oil-cooled superbikes ever made, capable of producing and withstanding massive amounts of horsepower. That’s where a man like Yohann “Yo” Kostrzewa comes in. Yo began modifying bikes at the tender age of 18, and he went straight to the limit:

“My first custom build was an 1100 ZRX pumped with NOS — a real road-wrecker.”

Yo also developed a passion for American V8s, particularly Pro Street machines — drag-style street-legal cars tubbed for massive rear rubber. 

“Since the French are very passionate about US vehicles, I decided to import vehicles from the USA and resell them in France. To establish my business, I created KOS’THOR in 2009. This project, along with the logo, had been in my mind since I was 18.”

Yo picked up two GSX-R1100’s from a friend. The first he built into a Yoshimura-style endurance racer (pictured below), with a 1216 Wiseco engine, racing carbs, and endurance camshafts.

The second had been in an accident, but the 1990 GSX-R1100 engine was undamaged…and what a unit it was. The 1300cc stroker motor was prepped by none other than legendary UK tuner Dave Dunlop of Fast By Me Turbo Systems, who added an FBM turbo kit with a Garrett GT2860. 

Yo salvaged the engine from the wrecked machine and built an entire bike around it, utilizing an ’89 GSX-R750 Slingshot frame.

“I decided to rebuild it entirely as a Pro Street bike, keeping the original details. I went all-out with a NOS kit — a drag bike enthusiast since childhood, I wanted to build a signature KOS’THOR motorcycle.”

The bike has a dual-bottle NOS kit capable of 25-100 hp, with a lock-up clutch to transfer the power to the ground. The swingarm was extended 16cm to try and keep the nose down — good luck! 

The forks come from a ’92 GSX-R750, the wheels from a ’93 GSX-R1100, and the rear shock is a YSS unit. Yo rewired the bike from scratch, installed a steering damper and racing radiator, and much more.

“All the hoses are braided stainless steel. I modified the fuel tank to have two separate high-flow lines to feed the fuel rail during normal operation, and a separate line for the NOS kit’s fuel pump.”

The fairings, which comes from German specialists Ricambi-Weiss, were painted by Yo’s friend Loic Clément in ​​a “750RR” style.

Nicknamed Pro Street 51 or simply PS 51 for the year of Yo’s late father’s birth (1951), this turbocharged, nitrous-boosted monster is capable of over 400 hp at maximum boost (2.3 bar / 33 psi). Yo is currently running the bike at a “modest” 0.8 bar (270HP) with a 50-hp shot of NOS. 

For an experienced rider like Yo, it’s still unlike anything else on two wheels…or four:

“I’ve ridden a lot of pretty powerful vehicles, like I was saying, I ride a 2018 ZX-10R on various tracks in Europe and I also own a Porsche 997 Turbo, but honestly, I’ve never experienced anything like this… It’s like a giant elastic band is pulling you forward when the turbo kicks in. It’s a real catapult.“

We believe it. And know 18-year-old Yo, who had the idea for KOS’THOR even then, would be damn happy and proud of what his elder self has accomplished, both with this bike and his business in general. Bravo, Yo! 

Below you’ll find our full in-depth interview with Yo about the build, along with many more photos and details. We look forward to featuring more machines from his kustom kulture heaven in Lorraine, France.

Turbo-NOS GSX-R1100 Slingshot: Builder Interview

• Please tell us a bit about yourself, your history with motorcycles, and your workshop.

My name is Yohann Kostrzewa, aka Yo, I’m 48 years old and I live in Lorraine, France.

I’ve been passionate about motorcycles since I was very young. I started modifying my first bikes at 18, after getting my license. My first custom build was an 1100 ZRX pumped with NOS — a real road-wrecker. Very quickly, I also developed a passion for American V8s, and I acquired a 1967 Camaro Prostreet, registered with the NSRA, which I imported from Florida. Since the French are very passionate about US vehicles, I decided to import vehicles from the USA and resell them in France. To establish my business, I created KOS’THOR in 2009. This project, along with the logo, had been in my mind since I was 18.

Today, KOS’THOR has a strong presence in France and internationally within the KUSTOM KULTURE scene. From custom motorcycle builds, cafe racers, drag bikes, and track bikes (I ride a ZX10R on the track), to restoring VW Buses and Bugs, drifting, and gripping with the Legend Car, KOS’THOR is involved in all areas.

I’m not a professional, just a passionate enthusiast who lives and breathes his passion.

• What is the make, model, and year of the donor bike?

SUZUKI 1100 GSXR 1990 (engine).

• Why was this bike built?

I bought two Suzuki 1100 GSXRs from a friend who was selling his bikes.

The first one wasn’t in very good condition, so I completely rebuilt it in a “SUZUKA Yoshimura” style, with a 1216 Wiseco engine, racing carburetors, and endurance camshafts.

The second one (the turbo) had been in an accident, but the engine was barely broken in. I decided to rebuild it entirely as a Pro Street bike, keeping the original details. I went all-out with a NOS kit — a drag bike enthusiast since childhood, I wanted to build a signature KOS’THOR motorcycle.

• What was the design concept and what influenced the build?

A turbo engine isn’t common, so I wanted to push the envelope. Since I was 18, I’ve been passionate about drag bikes, NOS kits, turbos — I love and collect Simpson helmets, etc.

I’ll be 50 soon, and the goal was to show young people that there’s more to life than Ducati Panigales 😂😂😂. When I embark on a custom build, I go all the way — when I build a chopper, for example, I push it to the limit: suicide controls, rigid suspension, etc.

• What custom work was done to the bike?

I only salvaged the engine and built a complete motorcycle around it. The engine was just broken in; it was prepared by Dave Dunlop in England. It’s a 1300 stroked engine with Hayabusa pistons and connecting rods. It has an FBM TurboSystems (Dave Dunlop) turbo kit with a Garrett GT2860 turbo. The turbo pressure can vary from 0.4 to 2.3 bar.

• I decided to add a NOS dual-bottle kit to emphasize the Pro Street look.

• The clutch is a lock-up type to allow for power transfer.

• It has Nology spark plug wires.

 

• I decided to mount this complete engine in a 1989 750R frame.

• The forks are from a 1992 GSXR 750.

• The swingarm from an 1100 GSXR was lengthened by 16 cms.

• I added a YSS shock absorber.

• The front and rear wheels are from a 1993 1100 GSXR.

• The radiator is a KOYORAD racing radiator.

• All the hoses are braided stainless steel. I modified the fuel tank to have two separate high-flow lines to feed the fuel rail during normal operation, and a separate line for the NOS kit’s fuel pump.

• The fiberglass fairing from Ricambi in Germany was completely painted by my friend Loic Clément – ​​a 750RR paint job.

• I completely rewired the bike, starting from scratch with the original components: turn signals, horn, high beams, etc.

• I fitted a steering damper to the right side for those lightning-fast accelerations.

• Does the bike have a nickname?

PS 51, or Pro Street 51.

1951 being the year of my father’s birth; he passed away in 2014. It’s the signature number at KOS’THOR. It’s on my personal vehicles and it’s my race number.

• Any idea of ​​horsepower, weight, and/or performance figures?

Turbo pressure can vary from 0.4 bar to 2.3 bar (180HP to 400HP)
With 4 NOS levels (25-50-75 or 100HP)
Currently I’m at 0.8 bar (270HP) with 50HP of NOS

• Can you tell us what it’s like to ride this bike?

I’ve ridden a lot of pretty powerful vehicles, like I was saying, I ride a 2018 ZX-10R on various tracks in Europe and I also own a Porsche 997 Turbo, but honestly, I’ve never experienced anything like this with this Turbo motorcycle. It’s very impressive. It’s like a giant elastic band is pulling you forward when the turbo kicks in. It’s a real catapult.

• Was there anything done during this build that you’re particularly proud of?

I think the final result makes me very proud. Everything, actually 😎

• Is there anyone you’d like to thank?

• Yes, I’d like to thank my friend, the painter Loic Clément, who did a fantastic job painting the bike.
• And also my friend Jean Damien from SPIRIT OF FIRST GSX-R.
• The Circuit of CHAMBLEY in Lorraine was used for testing.

More Photos

Follow the Builder

Web: www.kosthor.com
Facebook: KOS’THOR Motors
Instagram: @kosthormotors
YouTube: @kosthor736

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