Yoshimura history – 20

Yoshimura History #20: The Arrival of Tsujimoto, Schwantz and Suzuki GSX-R750

New Kids on a New Weapon

Coincidence or fate, in 1985, a group of “extraordinaries” appeared on the scene that would change Yoshimura and the world road racing scene. The “extraordinaries” were Suzuki’s revolutionary oil-cooled GSX-R750, Satoshi Tsujimoto and Kevin Schwantz.

The GSX-R750 was homologated for World Endurance Championship and All Japan Road Race Championship TT-F1 Class in 1985, and for AMA Superbike in 1986. The bike was equipped with a unique air and oil cooling system called SACS (Suzuki Advanced Cooling System) which removes waste heat from the engine not only by air cooling fins but also by spraying high volume of engine oil into the head cover ???? from the special orifice which locates right above the top of the cylinder head combustion chamber casting ???? as well as onto the underside of the piston crowns.

The cylinder block does not have water/oil jackets but has narrow pitched cooling fins, which are much narrower than those of typical air-cooled engines. The engine uses a dual chamber oil pump which provides low-pressure oil line for cooling the cylinder head and a high-pressure oil line for lubricating the crankshaft and other engine components, and is equipped with an oil cooler as large as a radiator on a water-cooled bike. This configuration is simpler and lighter than a water-cooled system, and is far more efficient than an air-cooled system.

The GSX-R750 featured a double-cradle frame made of square-section aluminum tubing and a square-tube aluminum swingarm with a monoshock rear suspension. While this was not much of an advantage in TT-F1 where modifications to the chassis are permitted, the lightweight and highly rigid frame was a great advantage in Superbike where all frames must be stock.

Yoshimura riders #30 Shosuke Kita, #55 Satoshi Tsujimoto and #01 Kevin Schwantz on Suzuki GSX-R400’s in the pit getting ready for the 1985 All-Japan Road Race Round 6 Suzuka 200km TT-F3 race. Fujio (in black cap) and Kevin’s father Jim (in black jacket) anxiously stand beside Kevin who broke his collarbone in the race just prior to the TT-F3. This was Kevin’s Suzuka debut and first visit to Japan. The GSX-R400 features an aluminum double-cradle frame and a water-cooled parallel four-cylinder engine.

Satoshi Tsujimoto, born on February 19, 1960 in Osaka, was an unknown racing rider with a height of 180cm (5.9ft). His most notable achievement then was an 11th-place finish in the 1984 Suzuka 8 Hours as an International B-class rider, riding a Kawasaki GPz750 in a frame built by Osaka’s Daishin Kogyo. In this race, he and his senior teammate Shinichi Kaneda had decided to complete the race without a tire change, and the strategy had worked brilliantly. It was the first race in which Tsujimoto won prize money.

It was mechanic Noboru Sakai who introduced Tsujimoto to Yoshimura. Chief mechanic Kunio Asakawa saw Tsujimoto racing in TT-F3 at the final round of the 1984 All-Japan Road Race season (on October 28 in Tsukuba Circuit). His first impression was that Tsujimoto was just a hulking, tall man and not at all flashy. Asakawa assumed that Tsujimoto with his height would be good at handling the big and heavy TT-F1 machines (Yoshimura’s however were the most compact and lightweight). Although Asakawa was vaguely planning to hire a tall foreign rider for the 1985 season, it didn’t matter where the person came from.

Also, Yoshimura already had Shosuke Kita, who had just switched from Kawasaki, for the 1985 All-Japan Road Race season. Kita was small in stature but had a great sense of riding and was able to handle the big Kawasaki TT-F1 machine very well. Yoshimura therefore hoped that Kita would be a good fit for the more compact Yoshimura race bikes.

Tsujimoto (in his race suit) waiting to enter the track for the TT-F1 race. His bike #50 and the mechanic in charge of it are next to Kita’s bike #3 and mechanic Takenaka, and in front of Kawasaki Team Green’s GPZ750R.

Thus, Kita became Yoshimura’s ace rider and Tsujimoto the backup rider. The team thought that Tsujimoto may turn out to be a great rider, but even if he doesn’t, that’s OK. They didn’t expect that much from him. Kita was contracted as a racing rider, but Tsujimoto was contracted as an employee of Yoshimura. So, Tsujimoto commuted daily to Aikawa, Kanagawa, like any other Yoshimura Japan employee, and worked on the machines (just did the polishing actually since he could not do any maintenance work).

As it turned out, however, Tsujimoto was faster on track than Kita. He rode tirelessly and responded faithfully to the instructions given during the test. He has cheerful and positive personality, which is not what one would call Japanese but rather foreign. Pop, Fujio, and the mechanics liked Tsujimoto.

Schwantz wheelieing #289 Yoshimura Suzuki GSX750E out of the final corner of the 1985 AMA Superbike Round 7 in Laguna Seca, in which he grabbed his second pole position of the season. Due to a delay in homologation for the GSX-R750, Yoshimura team had to extend the useful life of the GSX750E, but even with this air-cooled bike Schwantz was still able to achieve 3 wins out of the 12 rounds against its biggest rival, the water-cooled V4 Honda VF750F. He was then an unknown rider with only a 15th place finish in the Superbike Round 12 (riding Kawasaki GPz750F) at Mid-Ohio in 1984.

Kevin Schwantz, born on June 19, 1964 in Houston, Texas, was also an unknown racing rider until he participated in a rider audition held by Yoshimura R&D of America at the end of 1984 at California’s Willow Springs Raceway. At the audition, Schwantz performed a high-speed wheelie on the back straight of the Big Willow while displaying a carefree confidence as if he was enjoying all of it, along with a perfect control of his bike.

By having good kinetic (dynamic) vision, Schwantz can maintain a wide field of view even at high speeds, which consequently provides him the ability to control the bike with precision. If the dynamic vision is not as good as it should be, the field of view becomes narrower, and because the images cannot be recognized clearly, one falls into a kind of panic state and everything becomes hectic. Although kinetic vision improves with adaptation, it is no match for someone with a high level of kinetic vision from the beginning. Kevin Schwantz thus joined Yoshimura. His technique was crude, but he was absolutely fast and could be even faster.

This was how Yoshimura and Suzuki coincidentally got hold of the “3 tools” in 1985, but it was an unexpected team who scored the first success with the GSX-R750. In the opening round of the All-Japan Road Race Series, Suzuka 2&4 Race on March 10, rookie Tsujimoto finished in 3rd place, ahead of senior teammate Kita in 4th. In the following All-Japan Round 3 (the 2nd round for TT-F1) at Suzuka on April 21, Tsujimoto finished 4th.

The podium of the 1985 All-Japan Road Race Round 6 “Suzuka 200km” TT-F3 International A&B Class, where Schwantz (right) finished a very strong 2nd riding his first-ever 400cc racer, a GSX-R400. The winner was Yoichi Yamamoto (center) on a Honda RVF400, and International B-class rider Tadashi Fukumoto (left) on a Moriwaki ZERO X1 (powered by a Honda CBR400 engine) in 3rd place.

Meanwhile, at the 1985 Le Mans, which was out of the World Championship calendar (the 24 Hours of Le Mans and the Bol d’Or 24-Hours at the time alternated annually in the role as championship round), French privateer Team Zone Rouge of Marseille Moto Service (Guy Bertin / Philippe Guichon / Bernard Millet) took the victory riding a GSX-R750 by turning the tables on Honda RVF750’s. The Suzuki Endurance Racing Team (Herve Moineau / Richard Hubin) finished in 2nd place after Moineau crashed while running in 2nd. The result was a 1-2 finish for the new oil-cooled Suzuki GSX-R750’s. Both of these two GSX-R’s had a TT-F1 chassis and suspension built by Suzuki HQ, and were powered by a Yoshimura-tuned engine.

Yoshimura’s first result in the 1985 All-Japan Road Race TT-F1 Class came at the 5th round in Sugo (the 3rd round for TT-F1) on May 19. After setting the pole position in the qualifying session, Tsujimoto took the lead from the first lap and rode alone to victory. It was his first pole position and first win in the International A class. Both rider and bike were in top form.

Behind this victory was a new technology. From 1980 until then, Yoshimura’s first choice of exhaust for domestic races had been the Cyclone 4-into-1, which is ingeniously designed in correspondence to the firing order of inline 4-cylinder engine, but with Tsujimoto’s bike for Sugo they went with a 4-into-2-into-1 setup. The fabrication was done by mechanic Asakawa.

Although the Cyclone 4-1 produces more power than the regular 4-1 exhaust and has excellent output characteristics in the high-rpm range, there is a torque dip ???? a torque loss ???? in the mid-range. To eliminate the torque dip, Asakawa decided to try out a 4-2-1 setup, which would sacrifice some of the maximum output, but would produce more low and mid-range torque. The 4-2-1 pipe worked wonderfully in Sugo, where there were many mid-speed corners, and the final section of the track was all about accelerating out of the chicane.

On the day after the Sugo victory, Asakawa, Tsujimoto and others brought the winning trophy to the hospital where Pop Yoshimura was being treated for lung disease. It made Pop happy, but as soon as he heard about the 4-2-1 exhaust, he just said, “Ah,” and fell silent after that. Asakawa and his colleagues knew why.

Schwantz came to Japan for the first time to compete in the 1985 All-Japan Road Race Round 6 “Suzuka 200km” TT-F1 and TT-F3 races which were held on June 9. Schwantz was puzzled by Suzuka Circuit’s high mu (coefficient of friction) surface, saying, “It’s like riding on sandpaper,” and that his American style of riding, in which he slides the rear to turn, did not work at all. Schwantz crashed in TT-F1 (qualified 6th) but finished 2nd in TT-F3.

Team Yoshimura’s Japanese pair for the 1985 Suzuka 8 Hours, Kita (right) and Tsujimoto (left), with their #37 GSX-R750. The team decided to take off the lower fairing to prevent heat sag in this endurance race (but went with a full fairing in All-Japan Series). Kita, the senior of the team, qualified 6th with a 2:23.120 (the fastest of all Suzuki’s) and placed 6th in the final. He scored one win each in the All-Japan TT-F1 and TT-F3 in the 1985 season.

Before the Suzuka 8 Hours, Kita took his first victory since his transfer in the Round 7 of the All-Japan Road Race (Tsukuba, June 23), and Tsujimoto won the Round 8 (Sugo, July 7). From the spectators’ view, the oil-cooled GSX-R750 and Team Yoshimura seemed to be on the upswing, and their performance was improving as they prepared for the Suzuka 8 Hours.

Then an incident occurred during the race week of the Suzuka 8 Hours (the 3rd and 8th round of the World Championship). Pop, who had just left the hospital, complained about GSX-R750’s slowness on straights and demanded to increase the compression ratio of the engine. Normally such a thing would never be done in the field, but this time Pop was adamant. The engine was brought to Moriwaki Engineering HQ in Suzuka to mill the cylinder head. As a result, the straight speed seemed to have slightly improved.

Fujio knew what was happening. The oil-cooled GSX-R750 was losing power due to heat sag. This became more apparent during the 8-hour endurance race in mid-summer. Even if a slight power increase could be expected by raising the compression ratio, the heat generated by the engine would also cause a loss of power. It is meaningless unless the heat sag is fundamentally solved.

The final race was held on July 29 with clear skies, 32 degrees Celsius, and 156,000 spectators. With the entry of Kenny Roberts / Tadahiko Taira aboard Yamaha’s first TT-F1 factory machine, the FZR750, the competition was at an unprecedented level of excitement. The Yamaha Factory initially took the lead, but, at 6:58 PM, a valve dropped and blew their engine. Wayne Gardner / Masaki Tokuno aboard a Honda RVF750 took the win from behind. Team Yoshimura’s Kevin Schwantz and his senior teammate Graeme Crosby finished on the podium in 3rd place, and Shosuke Kita / Satoshi Tsujimoto finished 6th. Two SERT machines powered by Yoshimura-tuned engines finished 5th and 7th, and Team Suzuki Sweden finished 8th. Even with the heat sag, five oil-cooled GSX-R750’s finished within the top-10, proving that they have a good balance of speed and durability.

Tsujimoto had not forgotten what Pop had said to him shortly after the contract was finalized (presumably during his second visit to the company headquarters): “If you win the championship, I’ll take you to Daytona.” Tsujimoto repeated the word “Daytona” in his mind like a mantra as he ride through the 1985 season with the goal of becoming the All-Japan TT-F1 champion.

Yoshimura’s All-Japan series transporter filled with parts, wheels and weapons. From left to right: #30 Kita TT-F3, #55 Tsujimoto TT-F3, and #50 Tsujimoto TT-F1.

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Published on August 17, 2022

Stories and photos supplied by Yoshimura Japan / Shigeo Kibiki / Takao Isobe / Tatsuo Sakurai

Written by Tomoya Ishibashi

Edited by Bike Bros Magazines

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