Cycle News - Archive Issues - 2000's

Troy Corser's Aprilia RSV1000 ~llt.~-~~t.lr~ ~111·~~,Yill Like the singleton bike raced in '99 on a prototype basis by Peter Goddard. Troy Corser's 2000 Aprilia Superbike is based on the limited-run RSV Mille SP. of which a single batch of just 150 examples - the minimum quantity needed to homologate the model for World Superbike racing . were manufactured in 1999. None have been built since. Compared to the volume-production RSVlOOO, the Mille SP is in many ways a quite different motorcycle, with a more sophisticated chassis design housing a special short-stroke version of the April· ia 60-degree V-twin engine, which is only used on this model. So whereas the volume-production RSVIOOO's Rotax-built 996cc 'otto valvole' engine with chain-driven DOHC measures 97x67.5 mm - its torquey longstroke architecture, compared to its 98x66 mm Ducati/Suzuki/ Honda 90-degree V-twin rivals, tailored more towards real-world road riding - for its race-orientated Mille SP Superbike sister Aprilia has gone to the other extreme and produced a shortstroke 100 x 63.4 mm 996cc engine developed in conjunction with Cosworth in Britain, with a potential appetite for higher revs to deliver the power that wins Superbike races. Together with the bigger bore comes an increase in valve sizes, operated by the pair of chain-driven DOHC race camshafts per cylinder - inlets are up from 36mm on the stock RSVIOOO to 40.7mm on the SP, and exhausts from 32mm to 36.5mm, set at a flatter included valve angle of 30 degrees, compared to 32 degrees. Corser's factory Superbike always runs titanium valves fitted with single valve springs compared to the double ones used on the streetbike - all for the reduced inertia that permits higher revs. Similarly, to reduce friction, the forged 12.5:1 Wiseco pistons are of a two-ring design, which Aprilia race chief Giuseppe Bernicchia says don't experience any oil blow-by problems, fear of which prevented them being adopted on the street SP. Those pistons are fitted via titanium rods to a nitrided crank, whose design can be varied from track to track to offer different engine response via an altered mass, while the lower crank-driven counterbalancer fitted to iron out the vibes of the narrow-angle V-twin engine on the street Mille is still retained on the works Superbike. Although the road bike's secondary balance shaft mounted on the rear cylinder head has been jettisoned, in pursuit of a little extra power at the expense of some increased vibration. Revised engine internals are fitted on an ongoing basis, with factory tester Alessandro Antonello the first to employ them before passing them on to his Aussie teammate, though at this stage the red and matt-black Aprilia is still a little down on power to its main rivals, making Corser's feat in turning it into a consistent race-winner aU the more cred· itable. While Aprilia claims the street SP delivers 145 hp at the crank at 10,700 rpm, and Goddard's prototype didn't have a lot more than that at the rear wheel last season, in the guise that Corser raced it to five race victories this season (and we tested it in at Valencia) the Aprilia produces around 165 hp at the gearbox at 11,300 rpm, with the engine limited to 12,200 rpm. That's an improvement partially brought about by the twin-pipe Akrapovic exhaust system adopted for this season, and worth 5 hp more at the top end than the '99 single pipe system. This comprises a mixture of titanium and stainless steel sections fitted with carbon cans, with the front cylinder's exhaust header intruding through the center of the not particularly large but quite deep water radiator the Aprilia engine must be thermodynamically quite efficient in order to produce so much power with such a relatively small single radiator, though the oil cooler beneath it is quite big. But it still gives away anything up to 10 hp to its Honda or Ducati V-twin rivals, though the exact output varies slightly from track to track, depending on the fuel injection mapping via which the team tailors the power delivery to suit each circuit. However, for the final race of the season at Brands Hatch in October, Corser raced with an Evoluzione version of the 60-degree V-twin engine revving to 12,700 rpm - heady going for a big-bore motor still employing valve springs, 16 JANUARY 24,2001 • cue I • n • whose greater revs and extra top end power should be the basis for improved acceleration next season. The Mille SP engine employs sandcast-aluminum crankcases rather than the RSVIOOO's diecast ones, aimed at increasing strength and rigidity at the cost of a slight hike in weight which is partially offset by the magnesium side covers - while the cylinder design is a stiffer closed deck format, compared to the RSV's open deck design. However, the drysump engine's bottom end design is the same as on the stock Mille, with a lightweight external stainless steel oil tank low down on the left just forward of the engine, but an uprated lubrication system with a second return pump. Aprilia completely redesigned the transmission for 2000, to deliver the slipper clutch that was absent from the bike aU last season when Goddard rode it. This is adjustable for the degree of slip and incorporates a conventional rear-wheel cush-drive, so is quite different from Aprilla's patented PPC pneumatic system employed on the street Mille, and is now proven to be reliable, says Bemicchiao "The slipper clutch is absolutely compulsory for a V-twin," he admits, "but though we had it under development in '9 it needed a lot of work to find the right setup and to make it reliable. I think Troy is very happy with it now - it was the improvement he wanted most to see on the bike when he signed for us." However, there's no provision for an extractable six-speed gearbox as was first envisaged, for fear of reducing crankcase rigidity with the verticallysplit engine: the race team has to open the engine to change internal ratios, a three-hour job. "I think the chance to change the gearbox like on a GP bike is an Important option we must study for the future," admits Bernicchia. "For sure, because we have a problem with acceleration at the moment, we feel the absence of this more than if we had a very torquey bike - we can't close up the gearbox to get maximum drive out of important turns, and this compromises our top speed, because it takes longer to get there. Even on a V-twin, it's absolutely desirable to have this option, so although it will require the bike to be re-homologated, because it will entail a modified engine casting, this is something we must strongly consider in future." Ducati teams have been saying the same thing for years. The SP Superbike's Cosworth-developed cylinder heads are quite different from the stock RSVIOOO design, with the larger valves necessitating a single central sparkplug instead of two, plus revised porting and a smaller combustion chamber, which incorporates Cosworth's trademark five-axis machining process to optimize turbulence and cylinder filling, aided by inlet ports which for this purpose are quite straight. However, there's a longer intake length compared to the road bike, aimed at improving torque on this shorter-stroke motor. Compared to the single injector/51 mm throttle bodies used on the RSVIOOO and Mille SP streetbike's Nippondenso EFl, the Aprilia Superbike runs a fuelling package homologated in accordance with SBK regulations via a 50-off customer racekit, featuring bigger 60mm throttle bodies now with twin injectors per cylinder - one in a FormuVII' S la I-type external location directly above the intake trumpet, the other positioned just after the throttle butterfly. Chassis-wise, the Mille SP follows in the short-stroke engine's path of being tailored for racing, but in doing so breaks new ground both on the street, and for any Superbike racer. Basically, what Aprilia chassis guru Gaetano Cocco has done here is to bring the multi-adjustable chassis geometry of his World Championship-winning GP bikes to the Superbike grid: none of Aprilia's four-stroke rivals offers the opportunity to dial in such a wide choice of alternative chassis geometry. To achieve this, Cocco has produced a heavily-revised version of the RSVIOOO's aluminum twin-spar frame, with the V-twin engine located 5mm higher than in the stock Mille, to further compact the mass and reduce the polar moment, for more stable yet still responsive steering. But just as on Aprilia's GP two-strokes, the position of the engine within the chassis can be altered to optimize weight distribution and handling - 5mm up or down, 2mm forward or back. This, for example, avoids the problem that Honda had to grapple with throughout the life of the four-cylinder RC45, in having the engine essentially in the wrong place for ideal handling, but unable to alter it without building another batch of streetbikes to re-homologate the altered geometry. In addition, while 20-percent stiffer than the stock Mille frame for the same weight, the SP Superbike chassis has an adjustable pivot at the rear for the heavily braced twin-sided swingarm. This uses an Ohlins shock, while up front the reinforced steering head allows the fork angle to be altered one degree either side of the stock 24.2-degree rake. The adjustable triple damps housing the 42mm Ohlins racing forks also allow trail to be varied 6mm either side of the stock 95mm setting, while at 1405 mm the stock wheelbase is quite contained for a big V-twin - though Corser's preference for different chassis geometry compared to Goddard, meant the team had to basically throwaway all the settings they'd acquired in '99, and start again. "To begin with, we made constant changes in testing," says Bernicchia, "especially the swingarm pivot position and rear link. But now we alter it very little from one track to another - Troy likes a more balanced setup, with a longer swingarm, slightly wider head angle, less offset and lower rear ride height. But after we got the right setting for him in testing before Misano, we only fine-tune it for each new track." Thanks to copious use of carbon fiber, the Aprilia presently weighs in at 365.2 pounds half-dry, 6.8 pounds over the World Superbike minimum weight limit - "But we're getting there!" insists Bemicchia, "although we'd like to have the benefit of fitting an electric starter, like Honda - they must have worked very hard to make their bike light enough to afford this luxury! In fact, I think this is the future of Superbike racing - it should be compulsory to carry one." Thanks to the compact mass of the 60-degree motor, weight distribution is excellent by V-twin standards, with a 54/46-percent frontal bias which helps glue the front 16.5inch Dunlop tire to the track. 320mm Brembo twin discs are fitted up front, gripped by the Italian firm's latest radially mounted four-piston calipers. The Aprilia looks quite the most voluptuous - okay, bulbous - machine on the Superbike grid, a fact reflected in the bike's aerodynamic qualities, for the stock Mille SP is the first production streetbike to break the benchmark 0.30 Cx barrier in wind tunnel testing. "People say it looks porky, but it doesn't feel that way when you ride it, and in fact we've got it steering a little better than the narrower Ducati," says Corser. "I reckon it's a visual deception caused by the color scheme, which makes it look wider than it really is, especially at the front. And for sure you can tuck away better behind the screen than on the Duke, which probably explains why our top speed isn't so bad when you eventually get there. It's top-end acceleration that's our problem, even on the Evo-bike - midrange is fine, which is why it works so good on tighter tracks. But I hope the new Evo motor will do the trick - it's got every promise of doing so." Corser and Aprilia to put a third kind of V-twin at the head of the Superbike World Championship standings at the end of the coming season? Don't bet against it.

• Cover