Ducati Desmosedici GP7, Yamaha YZR-M1, Honda RC212V - MotoGP Rides - Special Section

Fiat Yamaha YZR-M1 800 Tech
Yamaha's R&D team, headed by YZR-M1 project leader Kouichi Tsuji, developed a contender for the new 800cc category that was substantially based on the previous 990cc bike, aiming to retain the advantages of its inline-four-cylinder format and especially the proven chassis design. Rossi struggled for much of 2006 with midcorner chatter problems that were only resolved with the introduction of a new Deltabox frame design with altered rigidity specs for the final five races of the 990cc era. "After we found a chassis that performed satisfactorily, we were reluctant to discard it for the new formula," says Yamaha race boss Masao Furusawa. "So we retained the same essential format and developed an engine which took many lessons from our final-version 990cc power unit."

The DOHC 16-valve, inline-four-cylinder engine's overall dimensions are naturally reduced compared with the 990, but the overall bore-and-stroke ratio is less oversquare than the bigger motor's ultrashort-stroke layout, according to Tsuji, to regain some of the torque sacrificed by the smaller displacement. The new engine is 3.5kg lighter and physically smaller than the 990, measuring 8mm narrower overall and 18mm shorter from the top of the cylinder head to the crankshaft, which is also 5mm closer to the swingarm pivot cast into the crankcases. The Nikasil cylinders carry two-ring aluminum pistons machined from solid metal, mounted on titanium conrods. As before, the aluminum crankcases are likewise machined from solid billet. The complexity of the CNC programming necessary to carve all these components from solid lumps of metal is obviously significant.

Yamaha retained the so-called "long bang" format of the 990cc bike on the 800cc motor, with the firing pulses on two cylinders closed up to around 60 degrees of crankshaft rotation, followed by a space of around 300 degrees before the next pair fire close together, intended to enhance traction and tire life. Like the 990, the YZR-M1 800 motor's crankshaft rotates backward, with an intermediate shaft located between the crankshaft and dry clutch. This is also fitted with weights to act as a counterbalancer, thus eliminating undue vibration resulting from the uneven firing order. The Termignoni titanium exhaust is now the only one on the MotoGP grid to be fitted with a silencer, because Rossi claims a loud exhaust robs him of concentration. Yamaha can afford the weight penalty this entails; the YZR-M1 800 weighs 328 pounds with oil and water (no fuel) just like its big brother did, 1kg more than the MotoGP weight limit-and for the same reason. "We need to be sure it is this way at the start of a race, since by the end when weight is checked, we will lose up to 0.8kg from tire wear and oil consumption," Tsuji says.

Yamaha used conventional valve springs in the engine for most of the '07 season with the belief that engine revs for the new-generation 800cc bikes would be limited by fuel consumption. "We believed that the new 21-liter fuel tank regulation would mean that engine speeds could not exceed 18,000 rpm without running out of fuel in a race," Furusawa admits, "and at these rpm it is still OK to use valve springs instead of a more complex alternative technology." This explains why Yamaha got smoked in the first race of the season at Qatar, when computer projections for fuel consumption caused them to back off engine speeds to 17,500 rpm, resulting in Stoner's D16 GP7 being timed at 202 mph down the Losail pit straight, against just 192.6 mph for Rossi's Yamaha. When it was discovered afterward that Rossi's bike still had more than a liter remaining in the fuel tank-against just a third of a liter for Stoner-Yamaha realized its mistake and raised revs to 18,000 rpm for the next race in Jerez, which Rossi duly won.

But even more revs weren't sufficient to keep up with the flying Italian bike that ran 209.4 mph versus the YZR-M1's 202.5 mph at Shanghai, where the Honda and Kawasaki were both faster, too. This forced Yamaha to accelerate development of a pneumatic-valve version of the motor, which debuted in postrace testing at Brno in August and was judged sufficiently promising for Rossi to race it two weeks later in Misano, only to DNF with a blown engine.

When a repeat failure occurred in testing in Japan, the decision was taken to park it on the sidelines for the time being, especially as Yamaha had by now developed a fourth version of the existing valve-spring motor, whose revs had been raised to 19,000 rpm without affecting fuel consumption and seemingly without any ill effects in terms of reliability. This proved a wise decision when Rossi won in Portugal using that uprated motor, delivering four percent more horsepower than at the start of the season.

The full ride-by-wire electronic throttle Yamaha introduced on the 990 last year is retained, but the lighter and more compact Magneti Marelli Marvel 4 ECU used this year delivers enhanced engine management that now includes the ability to alter engine mapping for every corner, as well as for each gear ratio selected. Tsuji confirms the ECU now recognizes each individual turn on the track, via an onboard GPS receiver. And most importantly, the Marelli ECU is now programmed to make extremely precise calculations for fueling the motor, which are thought to include the facility to automatically lean the engine out in any given corner to save fuel, before richening it up again for speed down the straight, as Ducati is known to do via the same ECU.

Comparative telemetry from Jerez of relative performance between the 990 and 800cc Yamahas showed that on the smaller bike, Rossi brakes 30 meters later and opens the throttle 15 meters earlier than on its more powerful predecessor, using about 10 percent more throttle overall than on the 990. And while this had a 3-5 percent faster top speed-about 6 mph quicker down a long front straight like the one at Mugello-the 800 is anywhere from 2-6 mph faster in turns. This underlined the critical ingredient of chassis design in creating the new bike. "The YZR-M1 frame is designed to keep the vertical stiffness and reduce lateral stiffness and torsion," Tsuji explains. "This is because when the bike is banked, the frame must also act as suspension. That is why we focus very much on this element with many tools and simulations, and why in 2005 we removed the cross-member of the frame. This reduced lateral and torsion stiffness and gave much improvement for agility and stability."

After thick 47mm Ohlins forks were also debuted at Mugello in an effort to give Rossi better feel during braking, overheating problems resulted from the big forks cutting off cooling airflow to the radiator. A new fairing was introduced at Brno to fix this, and that's what was on the bike at Valencia. The long swingarm delivers not only enhanced stability and traction in what is understood to be a relatively short wheelbase by current MotoGP standards, but also helps improve grip from the front 16-inch Michelin adopted this season, mated to a 16.5-inch rear. The reason for using a 220mm ventilated steel disc at the rear, in contrast to the big 320mm carbon discs up front, is a simple one, according to Tsuji. "Both riders use the rear brake, but not often enough to keep it warm if it is made of carbon," he explains. "So we must use a steel disc for immediate response-and because we are already on the limit, the extra weight is not a problem."