Many will not understand the endless fascination this engine/project has; and continues to generate, for me.
There are so many technical innovations, encapsulated within this engine, it isn’t difficult to see why it took Alfa so long to bring it to market.
I think I understand why the Vauxhall and SAAB, 2.8T versions are probably more reliable, not least because they have VVT on the inlet valve timing, whilst the exhaust timing remains fixed. Their Turbos provide an external EGR function, which is much more predictable and their twin rotors whilst utilising spent exhaust gas energy, also simplify the exhaust system.
But, it is what it is! An Alfa; and much more sophisticated than all my previous Alfa’s.
I have just spent many hours researching “Engine Braking” and the effect NVO has on drag. It is clear to me it has a tremendous influence on braking efficiency and it leads me to believe I need to update my brakes.
For engine braking to be effective, the engine, when the throttle is closed, must exert a counter force upon the drive system. In doing so, this must transfer energy to the rear faces of the timing chain system and thus place considerable force on the timing chain tensioners - trying to drive them back into their housings.
Under normal circumstances, these tensioners are simply taking up slack! However, whenever there is “Reverse drive” - force coming back from the gearbox - the pressure is enormous and on inspection the internal “ratchet” of the tensioners, which adjust as the chains stretch, do not seem man enough. Indeed, I have seen pictures where the “Pin/Peg” inside the tensioner has sheared off.
This scenario is exacerbated by virtue of Alfa’s choice of valve timing, ie. NVO.
Beyond knowing what the static valve timing angles are when the engine is switched off, I cannot hazard to guess what they may be dynamically. All I can say is, with conviction, it creates a great deal of drag when lifting off the throttle.
But, according to a lot of research material, NVO can play a great role in reducing pumping losses, increase engine efficiency by 7% - according to one eminent study - and improve performance on light load, whilst reducing emissions.
PVO however, is not so good at dealing with emissions. But that can be effectively dealt with by Catalytic converters and constant Lambda monitoring of exhaust manifolds. It seems also, Alfa got it wrong wrt pumping losses as the valve timing creates substantially more than when NVO is replaced by PVO. Throttle response is dramatically improved.
I have watched so many YouTube videos of 159/Brera, where the sounds of various exhaust systems have been compared. Whilst many have been “Aurally Impressive”, everyone that I have viewed have demonstrated varying delays in engine “Pick -up”: where the driver, stabs the throttle, the engine responds meekly, pausing, then finally getting going, picking up.
To what do I attribute this too? So many things are interrelated, all having a knock on effect and all, in this instance; imho, having a detrimental effect on performance.
1.) Poor VVT response time - unless valve timing changes rapidly, the engine will not respond quickly to throttle inputs. This is categorically due to poor oil flow/pressure within the engine.
2.) Manifold Cats - the restriction they present to exhaust gas flow, guarantees any potential for scavenging is greatly reduced.
3.) Twin Cat - neglecting the appalling fabrication work, conjoining the two paths after the catalysts, where the exhaust diameter increases, ensures no negative pressure can exist to assist in scavenging. Furthermore, the restrictions, the canisters present to the forward flow of exhaust gases, is applicable also to reverse flow, further attenuating whatever scavenging Alfa’s choice of valve timing could create.
4.) A performance engine, such as the 3.2 JTS; particularly given its 11.2:1 compression ratio, should have a healthy VVT range, to generate good torque characteristics across its range. Valve timing of the order of - inlet 6deg. to 10deg. BTDC: exhaust the same, ATDC. However, the 3.2 JTS Exhaust static is 9deg. ATDC, their Inlet is 11.5deg. ATDC.
The VVT range of the 3.2 JTS inlet is 50deg., from -11.5deg. ATDC to 38.5deg. BTDC. Thus as far as performance is concerned, 11.5degs. do not come into the equation. And if one accepted a static timing advance of 6deg. for the inlet valves, the effective range of the inlet VVT is 32.5deg. compared to a fixed valve timing engine, not very impressive at all!
However, the Exhaust VVT angles by comparison seem almost normal, from 9deg. ATDC to 41deg. BTDC. Also, it is undestood, the exhaust camshaft is disproportionately advanced on start - up, to assist in Cat warm up, via the NTC sensor in the water jacket of cylinder 2 exhaust port.
So it appears to be the inlet camshaft that is the main culprit with respect to NVO and its lack-lustre range.
5.) Poor VVT alignment of rear bank exhaust camshaft position sensor.
"Fact" - Bosche Specify their Position Sensors, which are "Hall Effect Devices", should be within +/- 0.5deg. of cutting the sensor field at 90deg. The rear bank is somewhere in excess of 10deg. out of limit. This has come about because the front cover to which it is mounted was not recast with the provision for vvt on the exhaust camshaft and thus the "Boss" is obstructed by another fixing which restricts correct alignment. The two front bank sensors and the rear bank inlet camshaft sensor are correctly aligned!
If they are not aligned to within this tolerance, the output levels quickly fall, resulting in timing errors and potentially the ECU failing to detect the "Trigger Pulse". Combine this with timing chain stretch and poor rear bank oil pressure and it is hardly suprising it is always the rear bank exhaust camshaft that signals failure first!
6.) Flats" cut across the dividing walls of the VVT Solenoid Supply, Advance and Retard Ports. The consequence of this is, the inability of the ECU to "Lock the Angle" chosen, such that the correct valve timing angle can never be maintained.
This causes the exhaust camshaft to be driven away by the internal spring pressure forcing oil from the advance port and into the drain, ably assisted by the rotating face of the cam lobe exerting pressure on the camshaft phasor sprocket.
This is equally true of the inlet camshaft which, although having a weaker internal spring - because cam rotation normally drives it in the retard direction, but in this instance is more readily "Shifted" from its position by vitue of the cam face/valve inertia forcing the oil out of the rotor, across the flats and into the VVT drain.
"So the valve timing angles, if they are ever set by the ECU locking the ports, are never held in position because these flats allow the oil to be forced out and their angles change from the optimum."
Compounding this - and a hint of the consequences of it can be detected in video clips; whereby there seems to be a delay before the engine revs up is: whenever the ECU is operating the solenoid valves, the flow rate into the vvt rotors is reduced as hydraulic oil from the inlet port, bridges these flats and goes straight to the drain and back to the sump, via the head. This occurs, regardless of whether the ECU wants to advance or retard either the inlet or exhaust camshafts!
I shall not advance the case for fitting Colombo Bariani camshafts other than to say, I believe they recognised the issue of Valve/Piston interference is no different from that of any fixed valve timing engine, ie, there is sufficient clearance to enable a greater range of valve timing without interference, thus they increased the duration from 254/250 to 278/278, whilst maintaining the lift as standard. This has eliminated the NVO and created an inlet valve timing advance of 50.5deg. Maximum.
At the same time the range of the exhaust timing is now 23deg. ATDC to 27deg. BTDC. By the same token, increasing the static angle from 9deg.ATDC to 23deg.ATDC has meant that, on start - up, the NTC sensor needs to use a greater proportion of its temperature range, before the ECU finally rotates the exhaust camshafts back to a normal angle, and thus the "Noisy Period" of pre - heating the Catalytic converters is somewhat longer. Componding this is of course, the fact that there are no longer any Manifold cats to preheat and thus it is more noisy than hitherto, where the cats would tend to muffle the sound during pre-heating.