Slabside Thunderbike: ’88 Suzuki GSX-R1100 Racer

Road-Legal Racer: Haxch Moto’s Ex-TT GSX-R…

When Suzuki released the original GSX-R in 1984, it was a revolution in sport bikes — the closest thing to a racebike with lights ever to emerge from the Japanese Big Four. The aluminum-framed machine was nearly 20% lighter than its rivals, and performed like a fugitive straight from the racing paddock:

“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, rather than vice versa, as the case often used to be.” –Cycle World

The original GSX-R400 — only available in Japan — was quickly followed by the GSX-R750 in ’85 and the GSX-R1100 in ’86. These first-gen machines quickly earned the nickname “Slabside” or “Slabby” for the large slabs of plastic below the seats, developing a cult following that continues to this day.

The GSX-R1100 combined the many innovations of the 750 with big-bore power, making 130 bhp and 76 lb-ft of torque in the ultimate ’88 J model — last of the Slabbies before the introduction of the second-gen Slingshot.

Recently, we got in touch with Marc Bell of London’s Haxch Moto — a furniture designer, fabricator, and racer with a love for Japanese sport bikes of the late 80s and early 90s. Two years ago, after a high side on his Yamaha R6 at Cadwell Park landed him in Hull Royal Infirmary, he decided to get back to his roots:

“Not being a fan of injected bikes or hospital, I decided to follow what I truly love about bikes and come back next year to race classic bikes.”

After picking up the 1988 GSX-R1100J you see here, he made some very exciting discoveries:

“I stripped the bike back and found some nice frame and swingarm bracing, and also scrutineering stickers from the Manx GP, meaning the bike had been previously raced at the Classic TT — pretty exciting as I’ve followed the TT since childhood and have been over to watch both the TT and Classic TT in 2019.”

Marc set out to build a street-legal racer capable of competing in the Classic Racing Motorcycle Club (CMRC)…with an eye toward one day returning to the Isle of Man to race the Classic TT. The TT engine had been swapped out for a standard road mill, but a flurry of upgrades — Mikuni flat slides, Yoshimura Cyclone exhaust, reground cams with heavy-duty valve springs, and more — yielded 131 whp on the dyno.

Marc went full-bore from an aesthetics angle, too, designing and fabricating the aluminum tail section and outfitting the bike with a road-legal asymmetric endurance headlight:

“Appearance wise I wanted the bike to look like a proper classic 80’s race bike, as good in terms of quality as the factory teams of the day.”

After three trackdays at Snetterton, Marc had the Öhlins rear shock and GSX-R750 SRAD front end dialed in for fast, predictable handling. Though he discovered the newer front end would disallowed the bike for CMRC racing, the Slabby is legal to compete in the pre-injected “Thunderbike Ultra” series with Marc’s local racing club, and he hopes to bring the big air/oil-cooled Gixxer for a run around the Nürburgring this summer.

This season, Marc will have his hands full racing his FZ600 — the first round is this coming weekend — and he’s also just wrapped a new GSX-R1000 “Slabshot” build, which we hope to showcase soon.

Below, Marc gives us the full story on the build in his own words, along with more shots courtesy of photographers Roberto Garagarza and Harry Blaise Fryer.

1100 Slabside: In the Builder’s Words…

• Please tell us about yourself and Haxch.

I’ve always been into late 80’s / early 90’s bikes, Japanese sports bikes. My first road bike was an immaculate Nc30 VFR400, which I went on to race after binning it at a trackway and rebuilding it as a track bike. I also had the CBR400, a Slingshot 750, CBR900, and probably some others I’ve forgotten. I’d always been on the look out for a Slabby and when the chance came I jumped at it!

Haxch is my fabrication workshop based in London where I make lots of high end furniture, along with metalwork fabrications for interiors, designers, architects, and artists. I started off as a furniture designer myself and over the years taught myself the skills to weld and make things for other people, so have the eye still for proportions and styling.

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

Suzuki GSX-R1100, 1988 J model.

• Please tell us about the build.

Two years ago I had a huge big highside at Cadwell Park while racing an R6, last lap of the last race, and ended up being airlifted to Hull hospital with suspected internal bleeding. Not being a fan of injected bikes or hospital, I decided to follow what I truly love about bikes and come back next year to race classic bikes.

Not long after the crash while laying up, I spotted a nice Slabside that wasn’t stock and had potential for a build; I didn’t want to start with a nice stock example. I went to visit the guy, liked the look of it, and offered a straight swap for my CBR900, which saw me returning with the GSX-R1100 in the van and googling which class I could sneak it into.

I stripped the bike back and found some nice frame and swingarm bracing, and also scrutineering stickers from the Manx GP, meaning the bike had been previously raced at the Classic TT — pretty exciting as I’ve followed the TT since childhood and have been over to watch both the TT and Classic TT in 2019.

Discovering this history gave me the dream to get the bike and myself back to the island one day and race it again in the Classic TT, a goal which will take a lot of work from my side and a bit of luck too — probably 3-4 years realistically, but it’s possible and would be a great dream to achieve.

Despite the bike being at the TT, when we stuck the bike on the dyno it was only making 116 HP, so the TT engine must have been removed and replaced with a standard road engine. The meant the first task was to get this figure up.

We started with a new set of Mikuni RS38 flat slides with 30mm Mikuni bellmouths and a Yoshimura Cyclone full system — this gained a few HP but not enough. We then reground the cams for higher lift, fitted heavy duty valve springs, ignition advancer, and EBC clutch with heavy-duty springs and a beautiful billet aluminium top end oil cooling kit from Grumpy 1260. That all did the trick and got it up to 131 HP!

For handling the bike has Öhlins rear and SRAD 750 front end, although the first track session it was seesawing mid corner — this was then fine-tuned and now rides nicely. Before the build I did three sessions at Snetterton, then got covered in oil from the top end, so not a huge test but enough to get an idea of how it rides.

Appearance wise I wanted the bike to look like a proper classic 80’s race bike, as good in terms of quality as the factory teams of the day. A lot of people say there’s no point making a club racing bike look good as it’ll be down the road soon enough, but I don’t want to race something that I don’t like the look of, so intended to go all out.

It’s as important to me for the bike to look the part as well as ride well and was always my dream to own / build a bike to that level. Maybe the design background and furniture making has made me particular about form and finish, but that’s what I wanted from the build.

For proportions I tried the stock fibreglass tail section. However, it just didn’t look right, so I set out to design and build my own, starting with several cardboard models to mock up the form, then flattening these to draw the net up in Auto CAD so that I could laser-cut the panels in 1.5mm aluminum. I then shaped these with the bead roller and welded them up to make the final form.

The single-sided endurance light was added for looks but also to make the bike road legal so I can use it between track sessions for a Sunday blast on the twisties. I wanted to be able to use it year-round and not just limited to track. The plan is to take it to the Nurburgring in August and for that you need a road legal bike, so there’s another incentive!

Paint job again was designed to replicate the old 80’s bikes of the day but without being overly complicated. I’ve seen people making builds from slabbies recently and trying wacky colour schemes and I just don’t get it. It was classic all the way for this one, and it will be classic on the next.

Other upgrades include a Scitsu racing tacho (made in Sheffield), steering damper, Brembo discs, custom stainless screen brace, oil cooler with CNC aluminium bracket from Grumpy 1260, braided lines, braced frame and swingarm, and on the way from South Africa some rear sets made by ACC, again in billet aluminum.

Halfway through the build I discovered the CMRC (Classic Racing Motorcycle Club in the UK) wouldn’t accept my bike because of the SRAD 750 front end, so I’ll go back to my old club and race in the pre-injected series called Thunderbike Ultra — this has a power-to-weight ratio to keep things more even, but still I’ll have a tough challenge against the first-gen R1’s!

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

It’s great to ride. Flat-slide carbs mean direct responsive power when it’s up to speed on track — not so great round town and in traffic compared to CV carbs due to the nature of the design, but perfectly manageable and worth it for the extra HP.

Handling wasn’t great initially but after three trackdays I had it dialed in nicely and could start to push on a bit more. They’re old heavy bikes no matter what you do with them, but this one will definitely perform better than a stocker!

• Did you make it to the Nürburgring yet — if so, how’d it go?

Unfortunately I’ve not yet made it to the Nurburgring, work and life got in the way. However, there are discussions and plans being made for me a road trip over there this summer — fingers crossed we make it!

The plan this year is to race an FZ600 with CRMC (Classic Racing Motorcycle Club). The first round is this weekend — not even finished prepping the bike yet! Will let you know how it goes!