Technology of the new Ducati engine

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Technology of the new Ducati engine

Technology of the new Ducati engine
Now it’s getting tight

13 years ago, the four-valve twin of the Ducati 851 opened an unprecedented success story with many model updates. Now an engine with a radically changed head layout is opening a new chapter.

Jorg Schuller

12/27/2000

The time has come: After 13 years of conceptualism, it makes its debut Ducati with a new engine called the “Testa Stretta”. It initially replaces the four-valve V2 known as the “Desmo Quattro” in the top model 996 R to then drive all four-valve models step by step.
In principle, a lot remains the same: 90 degree cylinder angle, vertically divided housing, positively controlled (desmodromic), timing belt-driven valves. Compared to the previous top Desmo, the 996-SPS engine, the Testa Stretta gains strength over the entire speed range. A maximum of 135 hp at 10200 / min and 105 Newton meters at 8000 / min should be available, which roughly corresponds to the punch of the strong twin competition. In superbike trim, Ducati promises about ten horsepower more than its predecessor.
Testa Stretta means »narrow head«, which refers to the valve angle of only 25 degrees (previously 40 degrees). This creates space for larger valves (inlet / outlet new: 40/33 millimeters; old 36/30 millimeters), which are even somewhat larger in the superbike. Especially on the inlet side, the mixture now “falls” even more straightforwardly through larger ducts, and accordingly the throttle valve diameter increases to 54 millimeters as with the 748 R. With this, the new one also shares the remote nozzle principle of injection: one nozzle per intake pipe that goes directly into the intake funnel injects. It goes without saying that the top engine management from Marelli is used in the 996 R..
Thanks to the acute valve angle, the new combustion chamber and the valve pockets in the otherwise flat piston crown are flatter, which makes it easier for the flame front to move through the burning mixture. In turn, rapid combustion is unavoidable at the desired high speed level. Ducati is silent about the opening stroke of the valves, but certainly the flow cross-section, i.e. the area that is released by the valves for the gas throughput, is significantly larger than its predecessor.
One of the biggest problems with the new design was to design the desmodromic around the narrow valves and the renovated sewer system. Whereas in the old head the closer rocker arms and opener rocker arms were equally positioned towards the inside of the head, the bearings of the opener rocker arms in the new head moved outwards, while the closer rocker arms remained in their inner position around the spark plug hole (only M 10!) . What reads like a rime makes the less cramped desmodromic system more resilient and its advantages more usable: speed stability on the one hand, extreme valve kinematics on the other.
As a reminder: The desmodromic system opens and closes the valves without any spring support, so that the limit of the valve train’s capacity lies solely in its mechanical strength. In addition, particularly sharp valve opening and closing curves and correspondingly sharp valve timing can be achieved ?? which ultimately benefits the load exchange and thus the performance. In conventional valve trains, the springs struggle at high speeds to move the valves in a force-fit manner along the cam track, that is, to prevent them from “over-opening”, “late closing” or even oscillating.
The larger bore, which is accompanied by a sharper stroke-bore ratio: 63.5 to 100 millimeters compared with 66 to 98 millimeters, also creates space for the large valve disks, which are also widely spaced. Since the Aprilia mille SP and the Honda VTR 1000 SP-1 already feature this crank geometry, Ducati ?? “We have to remain pioneers” ?? already thought about a further tightening of the stroke-bore ratio. But even so, the speed level increases by around 600 rpm, which at least for the superbike should mean around 13400 rpm. Grown camshaft drive wheels take the higher speeds into account by reducing the load on the toothed belt during deflection. As usual, the crankshaft is roller, the connecting rods are still with slide bearings.
If the old head was made in one piece, the roller-bearing camshafts and bearings were pushed in from the side, the new one would mount its camshafts in directly milled-in plain bearings with bearing caps, with a conventionally screwed valve cover covering the whole. This also minimizes noise emissions. On the cast side, the new head has more filigree, more uniform walls, despite the supposedly higher strength, and also has more voluminous cooling channels. Assembly is easier, but the entire production process is a bit more complex.
Casting: As before, the oil pan is cast onto the housing halves, its shape is now strongly funnel-shaped, so that the suction opening of the oil pump is always in the oil, even during strong accelerations. The “Testa Stretta” is wonderfully five kilograms less than the “Desmo Quattro”. This is not the only reason why the development work seems to be paying off. In any case, Troy Bayliss has pulverized all lap records in the latest tests with the new superbike.

Technical data – DUCATI 996 R

Engine: Water-cooled two-cylinder four-stroke 90-degree V-engine, transverse crankshaft, two overhead camshafts with plain bearings, toothed belt-driven camshafts, four valves per cylinder, desmodromic, valve diameter inlet / outlet 40/33 millimeters, angle between inlet and outlet valve 25 degrees, opener rocker arm outside, closer rocker arm inside, wet sump lubrication, electronic intake manifold injection with one remote nozzle each, throttle valve diameter 54 mm, engine management Marelli 5.9, no exhaust gas cleaning, electric starter, three-phase alternator 520 W. Bore x stroke 100 x 63.5 mm Displacement 998 cm³ Compression ratio 11.4: 1 Rated output (DIN) 99.5 kW (135 PS) at 10200 rpm Max. Torque 105 Nm (10.7 kpm) at 8000 rpm Power transmission: primary drive via gear wheels, hydraulically operated multi-plate dry clutch, six-speed gearbox, O-ring chain, secondary ratio 36:15. Price including VAT 26,200 euros

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