Found a badge
for your car that was assembled in Pomigliano d'Arco by F.I.A.T SPA 
Let's be clear. Pomigliano d'Arco was never a 'Fiat' plant pre-takeover. It's the spiritual home of Alfa Romeo Avio and the place where the RA 1000 RC.41 engine was built (in the first factory), powering the Macchi C.202 in my avatar!. Might not be Arese, it's not Milan, but it's Alfa heritage.
I don't have any issue having Fiat Powertrain Technologies product (the TBi) under my hood.
Serious admiration for the technical knowledge conveyed in this informative thread. If only you were actually consulting to FCA...
Thanks, just relieving the boredom. Retirement isn't all it's cracked up to be.
OK, so now the 159 goes like she just lost 400 kilograms! However, she sounds like a German Panzer. Above 3000 rpm it really sounds great. Below, absolutely awful.
She always suffered from droning at 2500 rpm. So, with Autodelta Headers, the increased flow just exacerbated it. It didn't move, just became more obvious.
Cue - Supersprint Central section; no Resonator - droning now gone. But Alfa back boxes struggling with the level and starting to break - up, become ragg -ed. But at least it confirmed the issue surrounding the drone was related, if not entirely due to the resonator. However, having a spare Alfa twin cat, I long had my suspicions about that too!
Cue - New rear boxes. Dear me! An explosion of noise, filthy, scrambled noise and God, the level! But at least it confirmed my suspicions about the Alfa Cat. It can heard producing spurious products across the "Reed", which is formed by the way Alfa have crushed the twin cat outlets into one.
I reasoned, at low revs, the gas velocity across the Reed is sufficiently low to generate sound, similar to the way a clarinet. does. But in this instance, the two pipes join tangentially and where they Siamese, the edge is badly burred. Of course the capillaries of the two cats make it worse as they linearize the flow before the reed.
Cue - Supersprint Catalytic Converter. I have about three more weeks to wait before delivery. However the two headers will co-join; via the Flexis, at the input to this new cat. So it should help improve scavenging which Colombo Bariani Camshafts create, and the Autodelta Headers assist.
The camshafts alone, create 23.5 deg. of PVO, and how many carburettor-ed or Port Fuel Injected engines does anyone know, that can idle rock - steady at 750 rpm with that amount of valve overlap?
With the S.S. Cat, I expect the exhaust gases to be a lot cleaner - acoustically going into the S.S. centre section. However, I suspect the level to the new rear boxes will increase further and instead of waking the dead in Moscow, they will hear me coming in Beijing!
Solution - I really don't have one at the moment. The car drives like it has just shed 400 kilograms and above 3000 rpm it is glorious. At 4000 rpm, she is going like a missile - my wife complains it hurts her neck. There is no pleasing some folk! So whatever I do, I don't want to lose that.
Once, if, when, I get this sorted, I will need a new pair of rear tyres. They were new, less than 3000 miles ago. But there isn't much of them left now!
P.S. - Once the S.S. Cat is fitted and I doubt my problems will end there, I am going to try this device from Jetex Exhaust Systems - U936330, inserted into the S.S. central section, just before the "Y" which feeds the two back boxes. But I don't hold out much hope! Could be just snake - oil!