Total Motorcycle Website – 2005 Ducati 999R Exclusive – Page 4

Valves

The Testastretta engine of the new 999R uses titanium valves, both on the intake and exhaust. The weight saving is considerable, especially if we consider the strong accelerations imposed by the high engine speed. The valve diameter is 42 mm on the intake with valve lift of 13 mm, and 34 mm on the exhaust with lift of 11.5 mm. On the previous 999R’s engine the intake valve diameter was 40 mm with 11.71 mm lift and the exhaust valve diameter was 33 mm with 10.5 mm lift. The use of titanium has obliged Ducati to use special valves seats and guides.

The timing diagram has not been substantially changed relative to the previous 999R engine, although the cams are of a completely new shape. The intake valves now open by 21° before the TDC, compared with a previous value of 16°, and close 53° after BDC relative to the previous 60°. The exhaust valves open at 60° before BDC as before, while they close 20° after TDC compared to a previous value of 18°. The inclination of the intake and exhaust valves on the new 999R is no different from that of the old version, at 12° and 13° respectively off the cylinder-head axis. In line with Superbike race engines, the retaining system on the closing register valve stem has been changed. This register is acted on by the desmodromic timing rocker to close the valve, and its thickness determines the play between its surface and the fork-shaped ends of the rocker itself, with which it contacts. This play must be adjusted with great precision, since it greatly affects the mechanical stress on the timing components, as the valve returns to its seat. It also affects the timing diagram, which must be close to the nominal diagram.

The closing register retainer system normally used on series Ducati engines exploits the action of two half-rings seated in a cavity machined near to the upper end of the valve stem. These two half-rings engage the register. However, this system has evident limits on a race engine which is often run at its top engine speed. In these conditions the half-rings are severely stressed and tend to deform plastically (they are crushed) and hence do not guarantee a constant play between the register and the rocker. For this reason the Testastretta engine of the 999R uses two titanium half-cones which encircle the valve stem. They have a circular section bump on their inner surface which engages with the groove machined near to the end of the valve stem itself. This groove is however not as deep as that used for the half-ring system. Furthermore, the two half-cones, when the steel closing register is pressing against them, grip the valve stem under friction, thus considerably reducing the stresses around the groove. This enables the valve stems of the new 999R to be not 7 mm (as used on the other Testastretta engines) but 6 mm, resulting in a further weight saving. It is also worth noting that the half-cones, since they perfectly couple with the register, are not subject to deformation even though they are highly stressed. This means that the valve closure play remains constant for a longer time when the engine is running.

As already indicated, the valve centre distance has been increased over that on the previous 999R’s Testastretta engine. It has thus been possible to use parts with a larger diameter head. Each valve has been moved outwards (orthogonally to the ducts) by 0.75 mm, for an overall increase in stem centre distance of 1.5 mm (the new centre distances are 43 mm between the two exhaust valves and 46.8 mm between the two intake valves). The valve seats also have a higher position relative to those of the previous engine. It follows that they protrude more into the head combustion cavity, which has been completely redesigned along with the larger squish surfaces. The volume of the cavity is thus less than that in the heads of the previous model engine. As already indicated, the consequent increase in the compression ratio has been limited by reducing the height of the piston head.

The intake and exhaust systems

Nothing has changed in the new 999R’s intake and exhaust systems compared to the previous version. There is a single, large volume silencer, and the manifolds have no intersection points. In particular, the difference in length between the front cylinder manifold compared to the shorter rear cylinder manifold has been compensated for with a number of differing cross-sections (varying from 45 to 55 mm for the front unit, constant at 45 mm for the rear unit), so as to ensure identical fluid-dynamic behaviour of both exhaust systems. Furthermore, the rear cylinder manifold penetrates into the silencer.

The Testastretta engine used on the road version of the Ducati 999R is equipped with catalytic converters. Each cylinder assembly has a dedicated three-way catalytic converter. The one on the front cylinder is fitted about halfway along its exhaust manifold, while the rear cylinder unit is integrated into the initial section of the silencer. The airbox has a large volume (12.5 dm3 ) and is not closed off by the lower surface of the fuel tank. The ducts which lead the intake air from the dynamic scoops on the front fairing to the airbox are equipped with a Helmholtz resonator to reduce intake noise without penalising engine performance. The RH duct is integral to the coolant tank.

.

Page 1, 2, 3, 4, 5, 6, 7