Despite the current economic implosion, these are very good times to be sportbike riders. In the space of three months, we've been presented with two radically different alternatives to the sportbike status quo. First came the MotoGP-inspired crossplane-crank Yamaha R1. Now, hot in its tire tracks, comes the totally unique Aprilia RSV4, as fine a piece of clean sheet engineering as we've seen yet in the literbike class, with its ultra-compact 65-degree V4 powerplant. The fact that these two bikes proved so effective straight out of the box at the highest level, flanking the reigning world champion Ducati desmo V-twin—a third different option in superbike engineering—on the Qatar rostrum in the second race of the '09 World Superbike season, shows that each company did its sums right.
The chance to join journalists from all over the world at the Misano GP circuit in Italy to ride the production Aprilia RSV4 at the world press launch was initially subdued by the fact that it rained all day. Even in the dry, this is one of the MotoGP calendar's least-grippy tracks, and it becomes a skating rink in the wet. But close study of the weather forecast revealed that—just maybe—it'd be dry and bright the next day, and it was. Convincing Aprilia to let me have another go, this time in Italian spring sunshine, was the work of a moment. But at least this way I got to ride the Aprilia the way it was meant to be ridden, on a dry track.Having been conceived all along as an ultra-compact package ("The main objective was to make the bike as small and narrow as possible— we figured, ‘let's make a 250GP bike with a Superbike engine,'" said RSV4 designer Miguel Galluzzi) the Öhlins-equipped Aprilia RSV4 Factory waiting for me in pit lane looked dinky and small, as well as very beautiful. Just as beautiful was the ultra-distinctive growl when you thumb the start button on the RSV4. This is one of the most distinctive-sounding streetbikes ever made, sounding like a high-pitched twin at low rpm, but a deep-voiced four up high. "We did quite a lot of work on the sound," admits Galluzzi with a smile. "We made 150 different variations on the exhaust before we settled for this one. It had to have a different character in terms of the exhaust note, but of course there's also a lot of power there, so we had to balance those two issues with the question of Euro 3 compliance."
The Aprilia chassis offers acres of ground clearance thanks to the slim motor, and an ease of steering that is truly addictive; even Honda's nimble, sweet-steering CBR1000RR doesn't have the lithe feel of the V4 Aprilia, and that's some compliment. The RSV4's pressed sheet and cast aluminum chassis weighs just 22.2 pounds, and its ultra-lightweight forged aluminum wheels surely play a part thanks to their reduced gyroscopic weight. Only the KTM RC8R matches the Aprilia in terms of the ease with which it flicks from side to side through a series of slow switchback turns without feeling nervous, or sacrificing stability through the ultra-fast fifth-gear sweeper on Misano's main straight. And the Austrian V-twin hasn't got the power-packed Aprilia's engine and top-end speed.The multi-adjustability of the chassis will help you dial in an ideal setting for any condition, even if you don't go as far as adjusting the engine's position in the frame. Just as on Aprilia's limited-edition '99 RSV1000 SP homologation superbike, and various editions of its 250/500GP two-stroke racers, the position of the RSV4 engine can be moved up/down/forward/back within the chassis, although Aprilia team manager Gigi Dall'Igna says the factory race team has only experimented once with this…then ended up moving it back to the default location! In addition to this, the steering head angle, the swingarm pivot height, and the rear ride height can all be altered, too. Softening the Öhlins suspension settings helped with grip in the rain, while in the dry the wheelbase was shortened via the huge 40mm range of adjustment for the rear axle location to help the bike turn better in the tight first section of the circuit without compromising stability in the faster bends.But the most impressive aspect of the RSV4 is the performance of that wonderful engine offering the best of both worlds between a four and a twin. To design the new motor, Aprilia hired one of Italy's greatest living engine progettisti, Ing. Claudio Lombardi, 67, creator of the fabulous Lancia Delta Integrale racecar that won four World Rally titles between 1987 and 1992, before he moved to Ferrari. After a stint as its Formula 1 race team manager, he then served as Technical Director until ‘94, where he moved to Ferrari's GT and sports car engine department, becoming responsible for creating the V8 engines powering many Ferrari automobiles today. The RSV4 is his first motorcycle engine design, created entirely in Aprilia's Noale base where he works full time.The result of Lombardi's efforts is a unique 65-degree V4 engine, with horizontally-split crankcases and the Nikasil cylinders cast integrally with the upper crankcase half for greater stiffness. "When we started work on the project in September 2005, the intention was to design a 60-degree V4," says Lombardi. "But it soon became clear that the intake tract was flawed. By opening the cylinder angle out slightly to 65 degrees, we had the straighter run that was needed to obtain our design target of 180 horsepower in street form." A single gear-driven counterbalancer in front of the cylinders consumes an estimated three horsepower in canceling out the vibration caused by the narrow cylinder angle. "It's slightly better balanced now than a 90-degree V4 engine," declares Lombardi with satisfaction, although he admits, "I don't pretend it's ideal, but it isn't an unduly tall engine package, either," referring to the fact that the bank of four 48mm Dell'Orto throttle bodies can't be sunk any lower between the cylinders owing to the narrow angle. "It's perfectly satisfactory in terms of height, and allows us to produce the narrow, compact motorcycle we were seeking."Despite the 999.6cc engine's seemingly radical oversquare 78 x 52.3mm bore/stroke dimensions, Lombardi says he'd have preferred an even shorter stroke, but was forced to settle on this configuration by the World Superbike rules then in effect. "At the time we were designing the engine, the FIM had imposed a 1.5:1 bore-to-stroke limitation on four-cylinder machines, to protect the 1000cc twins," he says. "By the time this restriction was removed from the SBK rulebook for ‘08, to allow 1200cc twins, it was too late for us to change. I would have preferred to have a shorter stroke, for more power at higher revs, while still retaining valve springs. I had experience at Ferrari with high-revving non-pneumatic valve engines, and it would have been good to adapt this technology to the RSV4."The RSV4's forged pistons deliver a high 13:1 compression ratio, with twin oil pumps ensuring adequate lubricant pressure at all rpm. To make the chassis as narrow as possible, Lombardi has adopted a modular cam-drive arrangement, with a chain driving the intake camshaft for each cylinder block, which in turn drives the exhaust camshaft through an idler gear, permitting a narrow 250mm cylinder head width across the top—less than the RSV1000 V-twin, according to Aprilia. The pairs of 32mm titanium inlet and 28mm nimonic steel exhaust valves for each cylinder sit at a very flat 22-degree included angle, and here once again Lombardi's F1 experience came to the fore. "At Ferrari, we experimented with an included angle of everywhere from 16 to 28 degrees," he says. "We found this was the best angle. I used titanium intake valves because you aren't allowed to change the valve material for superbike racing, and for 15,000-rpm engine speeds, you need titanium. Retaining steel exhaust valves was for economic reasons." Two springs are fitted per valve, and it's worth noting that the RSV4's water radiator is very small, indicating that Lombardi has achieved a high degree of thermodynamic efficiency for such a compact engine design. "I'm quite proud of that," he admits. "It was also an important issue in keeping the bike as narrow as possible. For a 180-horsepower engine, it runs very cool." He also reveals that Aprilia is already working on a bored-out 1200cc version of the engine. "Another advantage of the V4 layout is that you can easily change to a bigger bore," said Lombardi.
The Aprilia engine lulls you into thinking it's not revving very hard, until you look at the analog tach and discover that it is revving higher than you thought, thanks to that gruff exhaust note. It'll pull cleanly from as low as 3000 rpm on part throttle, helped no doubt by the Magneti Marelli engine management system that controls the throttle valves, the variable-length intake trumpets, and an exhaust powervalve. Similar to the Yamaha system, the Aprilia intakes use a 265mm-long intake trumpet for low rpm, with a servo motor separating the upper 35mm half at 10,000 rpm for better top-end performance.
source:http://www.sportrider.com