Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/128167
Alan Cathcart at speed on Chambon's version of the bike. Cathcart felt more comfortable on Fujiwara's mount, liking his softer suspension settings. and a titanium silencer. There's also a ported, flowed cylinder head which, for this season, incorporates revised valve seats and an altered shape for the team's own waisted valves, to allow a straighter hit of mixture from the 36.5mm throttle bodies. These valves are re-profiled to reduce them to the minimum weight allowed under Supersport rules, and are also fitted with new race springs that cure the valve float that was a limiting factor in revving the engine much over 14,000 rpm last season. Now, the engine's been dyno tested by Alstare to run for 10 minutes at 15,200 rpm I guess that's a fix! Alstare has also worked on increasing compression to 14.5: I , after countering initial overheating problems on some parts of the piston, and even went as high as 14.8: 1 in dyno tests before realizing they were sacrificing top-end speed in favor of improved acceleration - hence the cutback. They now have the engine tuned to the limit of the World Supersport regulations, to evidently good effect. It's worth noting that the intake stacks on the 36.5mm throttle bodies have differential length, even in standard form - though Bailly says Alstare uses 'different' ones that are shorter, with an altered shape for more top-end power. The most significant change this season was the adoption of a Magneti Marelli engine-management system to replace the Nippondenso/Mitsubishi ECU which comes as stock on the GSX-R600, and which the team employed last year. "This is much easier to remap and fine-tune, plus you can alter the revlimiter far more readily," says Bailly. "It has more break points for throttle position and engine speed, so you can refine the management system better, plus it's much easier to reprogram at the circuit. Last year, we used a Suzuki factory Superbike reprogrammer, which allowed us to remap the EFI cylinder by cylinder, injector by injector, as well as the two central sparkplugs which can be mapped together independently of the two outer ones. But this was very time-consuming - it took at least 45 minutes to make a new map, which eats up time at a track test or in practice at a race. So instead, we installed our optimum base map in the ECU for each circuit, and then used a Dynojet Power Commander to refine the settings. But adopting the Marelli ECU for this season has given us a much more sophisticated and capable real-time management system, which we can work on very quickly at the circuit." Riding Fujiwara's bike first at Zolder - exactly as he'd finished second on it four days earlier at Misano, just 86/1 OOOths of a second behind Foret's winning Honda after leading until the penultimate lap - before the Japanese ace took it over himself for some R&D testing, revealed how still more crisp and yet rideable the fuelinjected Corona Suzuki is compared to when I first rode it almost one year ago. Then, compared to the old 66.4 x 44.5mm carbureted GSX-R600 motor, the new 67 x 42.5mm Suzuki engine - the same ultra shortstroke format as the current CBR600 Honda - had felt notably sharper than the carbureted bike in accelerating from as low as 4000 rpm out of one of the Belgian circuit's trio of chicanes, even if the strong power kicked in only from 10,000 rpm upward. But there was a noticeable extra burst of power from 12,200 rpm - until the 14,300-rpm rev-limiter forced you to hit another gear and start over. What was effectively a pretty narrow, strong powerband made the Suzuki hard to ride to best advantage, since the engine cut-out felt to be set way too low - you could feel it still pulling hard as it fluttered the engine, asking for more revs to put the extra 8 hp it delivered over the previous carbureted bike to the ground. Frustrating. The 2002 Corona Suzuki is that rare thing - a bike which is more powerful than its predecessor, but also easier to ride. Not only is there 3 hp more than last year at the same 13,800-rpm power peak, the Belgiantuned engine now holds the power an extra 900 revs longer, thanks to the raised rev ceiling, and this wider powerband makes the bike much less work to ride hard. In fact, though it adopts exactly the same mechanical state of tune, the Fujiwara bike feels quite a bit different from the Chambon machine I rode immediately afterward. In fact, you'd swear they were two different models, there's such a difference. This is because Chambon prefers a bike which has a more aggressive power delivery, and to use the gearbox more to keep it driving hard at higher revs, whereas perhaps because of his 500cc GP background, Fujiwara likes a much more supple motor, which pulls well in midrange and where he can play the throttle to ride the torque curve up to peak rpm without changing gear nearly so much - but still flirt with the revlimiter in every gear. Yet his engine has a notably crisper throttle response and a sharper, though still controllable, pickup from 10,000 rpm upward, than his teammate's, which has a more aggressive nature and comes on stronger in the midrange, but seems to tail off slightly at higher revs compared to its sister bike. The Alstare Corona team has achieved these different characteristics exclusively via the engine mapping, says Bailly, which the Marelli ECU has permitted them to do at each circuit much more readily than before - basically, Fujiwara's engine employs less ignition advance and richer fuel settings than Chambon's. But the fact that the Suzuki engine's unique, three-way crankcase split allows them to tailor the internal gear ratios ideally for each rider is another factor. "We use a different gearbox for each circuit, and even so we still often change one or more ratios twice per race, on the Friday and Saturday nights," says Bailly. "But having collected the data we needed for the new bike at all the races last season means that we're in a much stronger position this year to achieve an ideal setup - engine as well as chassis." The benefits of the Superbike gearbox borrowed from the team's GSX-R750 works racer, whose rollerbearing ratios gain a crucial 1 hp on their own thanks to reduced friction, come into their own here in maximizing its Supersport kid sister's performance, allowing the team to swap internal ratios in just one and a half hours at a racetrack, choosing between any of up to six different options for each gear. The little Glxxer puts out 134 horsepower on the Alstare dyno. cue' _ n __ S • AUGUST 14, 2002 23