1985 Suzuki GSX-R750F: REVOLUTIONARY, Part 1
Words: Jeff Ware Photography: Heather Ware, Keith Muir
There is little argument against the general belief that the Suzuki GSX-R750F, the very first GSX-R750, was the first true four-stroke street superbike.
When it was unveiled in late 1984 at the Cologne Motorcycle Show in Germany, it sent shockwaves through the motorcycle world. With a full race fairing, aluminum frame, light weight and 100 ponies, it was built beyond belief. It was a true racer with lights and still is.
The bike was an instant game changer. I mean, show just about any red-blooded sportsbike enthusiast over the age of 40 a photo of a ‘Slabbie’ (nicknamed due to the slab sided appearance) 750 and they will drool and then say, “I wanted one of those soooo bad when I was younger.” Or, “I had one of those I wish I kept it…” The GSX-R750 had the same impact that the 1992 Fireblade or YZF R1 had.
Mind blowing. Nothing had ever looked so serious, being so light or so powerful and true to a racer replica.
It was faster, lighter and better looking than any motorcycle available. It also out-performed the two-strokes and came in at a competitive price. The same year, Yamaha released the FZ750 and Kawasaki was still pushing the GPz900R. Honda had the VF750 and VF1000. All of those bikes were brilliant but in terms of performance and weight, they were owned by the all-new ‘Light Is Right’ concept GSX-R750F. Stunning.
The brainchild of GSX-R Project Leader Etsuo Yokouchi, the GSX-R750 rewrote the sportsbike rulebook. Yokouchi-San was a firm believer in pushing technology to improve the breed in an era when many Japanese engineers were being too conservative. He also loved racing – and was the brainchild behind the Hans Muth designed Katana.
These two things combined gave him the drive and direction he needed to produce a four-stroke supersport bike that could out-perform the two-strokes, which were getting increasingly difficult to market and get through strict global anti-pollution restrictions.
So how did Yokouchi-San and team make the GSX-R so good? What made it so special? To understand that we need to look at what was going on in Japan back then.
Most big four-stroke superbikes at the time were simply beefed up versions of the Universal Japanese Motorcycle. They were heavy, poor handling but reliable and over engineered. We were used to bikes like Suzuki’s own GS range, the Kawasaki Zeds, Honda CB900 and 1100s, Yamaha XS1.1, these were big heavy bikes, with small brakes and low rent suspension, packaged up in flexible steel frames and finished off with narrow tyres. All of that was about to change…
At Yokouch-Sans direction, the GSX-R was developed through experience racing the GS and GSX750R, with Kiwi Graeme Crosby and Aussie brother of Warren Willing, Len Willing, (who I did my mechanical apprenticeship under at his shop Willing Motorcycles), riding the GSX750R in the Suzuka 8-Hour in 1984.
While the GSX-R was being developed, Suzuki released the RG250WE two-stroke and GSX-R400 four-stroke. Both gave the public and the other big three Japanese manufacturers a preview of things to come from Suzuki.
Mr Yokouchi figured if the GSX-R400 could be made 18 per cent lighter than its competitors then the scale could be applied to the GSX-R750.
The horsepower limit at the time was already an agreed voluntary restriction of 100hp so he knew that lightweight was the only way forward.
Before the project began, he had his engineers strip a GS750 and paint any parts that had not failed in the field blue and any that had failed red. When the parts were gathered together almost all of them were blue.
“We were too conservative. Nothing ever broke. Everything was over engineered”…
He set the target at 20 per cent less than competitors 750s. 100hp and 176kg was the goal.
Chassis development began alongside engine development. Mr Yokouchi also insisted on using the racetrack dimensions. “What works on the racetrack will work on the street. The motorcycle does not know where it is being ridden”… He started by using the 1983 Endurance World Championship winning HB Suzuki GS1000R ridden by Herve Moineau and Richard Hubin as a base to build the GSX-R from.
Styling was in the hands of the amazing Tetsumi Ishii who took as many angles from the GS1000R as possible. He did a brilliant job…
Since the release of the GSX-R750 in 1985 sportsbikes have gone full circle – lightweight, heavy, back to lightweight again but one thing is certain. Motorcycling performance can be split into two clear eras – the era before the GSX-R750F and the era after the GSX-R750F…
35-years on and the GSX-R750F is still a stunning looking machine. In fact, I rate it as one of the best-looking motorcycles ever released. I may be biased, as I own the example you see here, having bought it as a basket case and spending three-years doing a full ground-up restoration to get it back to as new. I’m now doing my third blue and white Slabbie build!
I ride the bike and I love it. It still holds its own and having owned RZs, RG500, an FZ750 and ridden many GPzs and VFs, I can tell you none come close to the handling and performance of the GSX-R750F for the era.
Don’t get me wrong – things have come a long, long way in 20-years and the old Slabbie would not even get close to catching the new 750 on the street or the track – but in terms of era, the 1985 bike must have blown the others into the weeds… I was 10-years old then but still remember seeing them on the showroom floor of the Suzuki dealership up the street. I’d ride my BMX bike rain hail or shine to gaze at the bike through the window and dream of owning one – which is why I have one now, 35-years later…
The engineers got that motor right – the fact that the 2020 model GSX-R750 engine is the exact same bore and stroke of 70mm x 48.7mm proves that, despite a swing to a short stroke 73mm x 44.7mm engine for 1988 and 1989, the factory reverted to the 70mm x 48.7mm engine in 1990 and it has remained that ever since, yet with modern cylinder-head technology, tuning, EFI, metallurgy and electronics it is now a whopping 50 per cent more powerful. Incredible.
1985 GSX-R750 TECH TALK
While competitors moved to water-cooled engines, Etsuo Yokouchi headed the other way. He wanted lightweight and minimal complexity.
Using the GS1000 engine and racing experience from the GSX750E, the GSX-R750 engine was designed.
The DOHC 16-valve inline-four-cylinder four-stroke featured a bore x stroke of 70.0 x 48.7mm, 9.8:1 compression, a wet multi-plate clutch and six speed close ratio gearbox. Water-cooling was ruled out as casting was not yet optimised, so the team used the same technique they had used on the XN85 Turbo, oil cooling using jets to squirt oil onto the bottom of the large pistons.
More oil than normal was also directed throughout the valve-train and upper cylinder-head and added extra oil capacity. Dual oil pumps move this oil swiftly around the engine and special channels help with fast flow. This was Suzuki’s new SACS (Suzuki Advanced Cooling System) and it allowed 100hp with no overheating issues. Every part of the GSX750E engine was redesigned.
The pistons were 10 per cent lighter, conrods 25 per cent lighter, crankshaft 20 per cent lighter, cylinder-head 22 per cent lighter and made of cast magnesium, cylinder block 17 per cent lighter and gearbox and clutch also tested and redesigned to be much lighter than anything seen before.
Fuelling was taken care of by competition level VM29SS flat-slide carburettors and ignition was by transistor type, which was standard for the day. The large airbox was under the false rear of the gas tank and the exhaust system a lightweight tuned four-into-one system.
The frame was cutting edge for the day. A lightweight aluminium cradle frame with a cast alloy headstock and side swingarm pivot plates held a box-section ally swingarm and cast aluminium triple-clamps. The forks were trick, with hydraulic anti-dive, Posi Damp, compression and preload adjustment and were a large 41mm diameter with 130mm of travel. The shock was a Full Floater unit with rebound and preload adjustment and 127mm of travel.
Another impressive feature on the 1985 GSX-R for the day was the brake system. Dual 300mm stainless steel rotors, Tokico four-piston calipers were strong and controlled with a Suzuki master-cylinder.
The wheels were cast aluminium, both 18in, the front wearing a 110/80 tire and the rear a whopping 140/70.
The chassis team was led by Hiroshi Fujiwara and was based on the GSX-R400. Only five castings and 21 tubes make up the GSX-R frame and it only weights 8kg.
Styling was based as closely as possible to the XR41 racer, which is why the GSX-R has an unmistakeable racebike look. Wind tunnel testing was a main focus and the winglets and screen came directly from the factory racer.
Next Jeff rides the 1985 GSX-R750F, the very bike he painstakingly restored for three years. Luckily it is insured with Shannons, just in case!
SPECIFICATIONS: 1985 GSX-R750
Claimed power: 75kW[100hp]@10,500rpm
Claimed torque: 68Nm[52ft-lbs]@8000rpm
Dry weight: 176kg
Fuel capacity: 18.5L
Engine: Inline four-cylinder, four-stroke, oil-cooled, DOHC
Bore x stroke: 70.0 x 48.7mm
Compression ratio: 9.8:1
Fuel delivery & Ignition: VM29SS flat-sides, transistor ignition
Exhaust: Four-into-one steel
Gearbox: Six-speed close-ratio
Clutch: Wet, multiple-plate, hydraulic actuation
Final drive: 530 O-ring chain
Frame type: Aluminium cradle, alloy box-section swingarm
Front suspension: Posi Damp Fork, adjustable compression damping and spring preload, conventional 41mm, 130mm travel
Rear suspension: Full Floater, rebound and spring preload adjustment, 127mm travel
Front brake: Dual 300mm stainless-steel rotors, four-piston calipers
Rear brake: Single 220mm stainless-steel rotor, two-piston caliper
Wheels: Cast aluminium, 18in
Tyres: 110/80 – 18, 140/70 – 18
Ground clearance: 140mm
Seat height: 755mm
Overall height: 120mm
Overall length: 2130mm
Instruments: Analogue tacho and speedo, couple of idiot lights.