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Testastretta
After several years of experience and success in the Superbike World Championship, the engineers at Borgo Panigale started to work on the Desmoquattro project again, to introduce a series of upgrades which had turned it into a totally new engine. The design of the 998cc Testastretta (NarrowHead) represented the state-of-the-art of high performance, transversally mounted twin-cylinder engines. The introduced modifications mainly (although not exclusively) concerned the top-end. The achieved results had led to the new characteristics and performance listed below:
- improved performance (performance meaning not merely an increase in peak power, but rather, improved response to the rider's throttle response throughout the rev-range)
- optimised and rationalised weights, thermal stress and mechanical stress
- improved reliability and decreased maintenance requirements
The new features of "Testastretta", presented with the new 996R at the Munich show on September 12th, 2000, can be outlined as follows:
Bore and stroke
In order to increase the maximum RPM, characteristic dimensions have been modified from bore=98mm, stroke=66mm (in the 996) to bore=100mm, stroke=63.5mm, in the 998. The increased bore has allowed to introduce two pairs of larger-diameter valves: the intake valve diameter has been increased from 38 to 40 mm while the exhaust valve diameter has been increased from 30 to 33 mm.
Cylinder Head Assembly
This assembly has been completely redesigned, basing on a detailed FEM analysis, which enabled a more rational use of internal thickness and to improve heat behaviour. Additionally, the new assembly is much lighter.
The increased bore has made it possible to use two pairs of larger-diameter valves: the intake valve diameter has been increased from 38 to 40 mm while the exhaust valve diameter has been increased from 30 to 33 mm.
The angle between the valves has been dramatically reduced (from 40° to 25°), to obtain a flatter-shaped combustion chamber (more efficient in terms of mixture combustion), and more consistent performance at the intake and exhaust ports. The engine will "breathe" in more mixture and burn it better!
The head body proper has been completely redesigned a detailed FEM analysis, conducted with the support of a primary specialised organisation, has enabled us to considerably improve this part's heat behaviour, via a rational, carefully studied thinning of the inner water jackets (the walls through which the cooling fluid flows) The final result was a dramatic weight reduction, while maintaining exceptionally good rigidity, necessary to withstand the high thermal stress and pressure levels typical of these engines.
The angle between the valves has been dramatically reduced (from 40° to 25°), to obtain a flatter combustion chamber which improves the surface/volume ratio, resulting in more efficiency in terms of mixture combustion; this modification has also produced more space on the valves' outside, resulting in more consistent performance at the intake and exhaust ports for better overall performance.
Timing
The timing accuracy of the camshafts and belt has been improved with a new system which will also facilitate maintenance. A larger, single central cover opens a much larger window to access the tappet area , which makes access for maintenance much easier.
The camshaft timing operation, performed when the timing belt is led through the special pulleys, followed by belt tensioning, has been brilliantly improved: a new system is now used to divide in two the keyed pulleys on the camshafts, so that the toothed belt can turn idle during belt tension adjustment, without pulling the cam.
Rocker arms
They have been completely redesigned basing on finite element analysis, and a 50 to 20% weight reduction has been obtained without negatively affecting their working life and reliability. The new rocker arm arrangement, achieved by moving their centres of rotation, has resulted in optimised thrust on the valves: the valve guides and seats are now assembled and then machined in a single phase. All this without affecting strength (under both load conditions, static and dynamic), in other words, without any risk of shortening the rocker arm working life.
Thanks to the new arrangement of the rocker arm rotation axes (or, positions of the axles on which they pivot), it was possible to obtain symmetrical opening rocker arms, thus eliminating the distinction, still applicable to the current head, concerning their installation side.
This new arrangement of the centre of rotation has been the object of in-depth studies, leading to an important result:the thrusts applied to the valves have been optimised, eliminating the unwanted flexural components which interfere with the smooth sliding of the stems inside their bronze guides.
The rocker arm pad has been improved, too: by grinding with a specially shaped wheel, a single, continuous surface has been obtained which ideally connects the cam matching area and its corresponding rocker arm face area. Thanks to the same system, the slightly curved face, necessary in order to offset the chromium hard-facing outward migration, can now be engineered in a much more accurate and repeatable manner than has ever been done in our rocker arms.
Camshafts
Increasing their outside diameter has increased rigidity. Weight has not increased thanks to their hollow design. The camshaft roller bearings have been removed: the camshafts now revolve on plain bearings under hydrodynamic lubrication conditions. By removing the bulky roller bearings, a considerable weight decrease has been obtained, unnecessary revolving parts have been eliminated and mechanical noise has been considerably reduced. The cam lobes, which determine valve opening and closing times, have been redesigned using very complex calculation systems, combining cam lobe design software with fluid-dynamic ducting process analysis software (Wave). The camshaft steel is no longer casehardened and hardened, but hardened and tempered, and then submitted to nitriding after machining: in this way, the best response to operating stress is obtained, thanks to considerable core toughness combined with high surface hardness.
Special care has been given to camshafts: the camshaft plays a key role in creating the Ducati engine identity, because it gives the engine its characteristic features in terms of dynamic, prompt response.The first, immediately visible modification in this part is a considerable increase in the shaft outside diameter: rigidity to stress has been increased, without any resulting weight increase, thanks to an almost completely hollow design of the shaft inside.
As already anticipated in the section concerning the crankcase, to support the new camshafts, the old ball-bearings have been replaced by plain bearings, at the core of which a fresh oil jet, combined with rotation, supplies the required hydrodynamic lubrication. By removing the ball-bearings' dead weight, we have obtained a considerably lighter assembly; we have eliminated unnecessary revolving masses (causing inertia) and considerably reduced noise, by supplying, as explained, fresh, clean oil not containing any foreign matter.
The cam lobes, which determine valve opening and closing times, have been completely redesigned; this is one of the most important parameters to achieve pre-set performance targets: by selecting a matched pair of cam lobes, you consequently select the valve opening angle of duration produced by that pair, the extent of the valve lift and its opening and closing speed. Once the initial phase of the angular positioning for that pair of cam lobes has been fixed, the opening advance, closure delay and overlap angles for the camshaft are also fixed.
Using very complex calculation systems, combining cam lobe design software with fluid-dynamic ducting process analysis software (Wave),it was possible to determine the power curve with remarkable accuracy, given the flowing parameters.
This enabled real-time correction and optimisation of that curve during the designing phase, to make it as consistent as possible with rideability and power output pre-set goals. New calculation strategies for acceleration control during grinding have produced extremely high-precision matched cam lobes, with a high degree of continuity among the various circumference arcs making up the individual lobes.
These two factors together have considerably reduced the amount of clearance (structurally never equal to zero) between the valve adjusters and the rocker arms: this resulted in a further reduction of noise and enabled to achieve more "daring" angles for the opening and closing lobes.
The camshaft steel is no longer casehardened and hardened, but hardened and tempered, and then submitted to nitriding after machining: in this way, the best response to operating stress is achieved, thanks to considerable core toughness combined with high surface hardness, obtained through a simplified production cycle.
Bottom end
Crankcase
Manufactured by sand casting, it has a new shape with the lower section designed to ensure oil suction even under hard working conditions (heavy acceleration, wheelies and late braking). Lubrication circuit
Oil to be fed to the camshafts and rocker arms is now taken from a part of the circuit downstream from the oil cooler. Oil that has already been cooled is therefore fed to the cylinder head. Increased working pressure and new filter type.
Transmission
Keying between the primary gear and crankshaft is no longer achieved with a taper and key system, but with a spline, nut and lock washer; the transmission shaft is now supported with more rigidity thanks to a double-row ball bearing. The design of the new 998cc Ducati engine is a major step forward in the field of high-performance, transversally mounted twin-cylinder engine design. Most of the parts making up the earlier 996cc engine have been totally re-thought and changed. The purposes of this project were, clearly, the purposes of any upgrade in sports engine manufacturing: improving performance (performance meaning not merely an increase in peak power, but rather, improved response to the rider's throttle response throughout the rev-range), optimising and rationalising weights, thermal stress and mechanical stress, improving the output capacity (both in terms of individual components and as far as complete unit assembly is concerned), better running efficiency for the customer, improved reliability and decreased maintenance requirements.
All this has been achieved by modifying the elements and components which we are going to review. For better clarity, this paper has been divided in two parts: modifications concerning the crankcase and parts contained in the crankcase, and modifications concerning the top-end.
Massive changes have been introduced in the new engine crankcase, that also respond to the requirements of the new top-end.
First of all, the engine lubrication circuit has a totally new design: oil suction by the pump pick-up is now carried out from a much lower position. The pick-up area design ensures total covering of the suction port under all working conditions, including the hardest conditions, such as heavy acceleration, wheelies and late braking typical of road racing.
The oil filtering system has also been improved by using a new, more efficient filter. This modification was necessary because of the changes introduced in the top-end, as we will see in the next section. The camshaft roller bearings have been removed: the camshafts now revolve on plain bearings under hydrodynamic lubrication conditions. Clearly, this requires the greatest cleanliness and total absence of foreign bodies in the lubricant: this is vital for correct operation of this mechanism, otherwise, matching parts would soon wear out.
If we examine the system which delivers lubricating fluid to the cylinder heads, we will observe that, while in the previous engine (996), oil to camshaft and rocker arm lubrication was taken upstream from the oil cooler, in the 998, oil is taken from that part of the circuit which feeds fluid from the cooler to the crankshaft: oil fed to the cylinder head has already cooled down, and is therefore more viscous and more efficient at helping the cooling fluid dissipate heat (it should be remembered that a few parts, sliding against each other during the delicate operation of the cylinder head mechanism, are hardly reached by any cooling fluid at all...).
Thanks to different sizing of the hydraulic parts of the pump, it was possible to obtain a considerable increase in the oil pressure throughout the circuit. This pressure is kept constant by using extremely reliable, purpose-built sealing parts.
The gear train operation from the crankshaft has also been considerably improved. This will have positive effects on both engine assembly and engine operation. These parts must necessarily comply with very strict standards of accuracy and rigidity. Keying between the primary gear and crankshaft, which was obtained with a taper and key system in the 996, is obtained, in the 998 with a spline, nut and lock washer. For an even better accuracy of the positioning of the drive gears, both parts have been submitted to super-finishing (honing) with a wheel shaped like an internal-toothed gear, which grinds all forms of this complex shape at the same time, and ensures a much quieter, more even mesh than the traditional grinding technique for case hardened gears (one tooth at a time).
Considerable advantages have also been obtained in the engine assembly phase, because the consistency achieved in drive shaft centres saves the assembler having to select a matched pair of gears that suit the production tolerances: any of the gear pairs available on the production line can now be used.
The transmission shaft, which transmits drive outside the engine to the driving wheel via the sprocket and chain, is now supported with more rigidity by using a double-row ball bearing; additionally, the chain and sprocket assembly is now fixed by means of a nut, instead of the earlier splined plate mounted out-of-alignment with the shaft spline. All this minimises the risk of slight misalignments of the chain and sprocket, which used to affect chain operation.
Finally, to complete the picture of the modified engine internals, a new neutral indicator sensor has also been used. The traditional electromechanical sensor, whose end would detect the presence of a "pip" in the gear selector drum, has been replaced by a simple electrical contact sensor: a resin split-ring (obviously, an insulating ring) is fitted in the gearshift drum. The sensor will only detect current flow at the point where the ring is split, by making contact with the metal from which the gearshift drum is made: this point obviously corresponds to the "neutral" position.
Careful redesigning of the pistons ensured an approximately 30 gram reduction in weight; the piston rings have not been spared either: slight modification of their thickness has considerably reduced air leaks from the combustion chamber, a phenomenon commonly known as blow-by.
The correct positioning of the lobes, with respect to the camshaft initial position (traditionally coinciding with the top dead centre of the horizontal piston, under maximum compression conditions) is thus obtained to a ±2° accuracy.
This enables to safely reduce the minimum clearance between the piston and valves during the "crossing" phase, and, especially in the racing version, to slightly increase the compression ratio if so required.
From the point of view of (scheduled or unscheduled) maintenance, the parts contained in the head assembly are now more easily accessible, thanks to a head architecture including a larger, single central tappet cover to replace the previous twin side covers. This opens a much larger window to the tappet area , which makes access for maintenance, replacement or adjustment much easier. Finally, a few words about the new suction manifolds, now manufactured from Viton®: this is an especially valuable polymer, highly corrosion resistant (and therefore not affected by contact with petrol or external agents). A labyrinth seal directly modelled on the manifold rubber enables us to eliminate any other seals between the above-mentioned flange and head body.
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Originally Posted by Ozboy 
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