I think that weak point of whole Alfa story about JTD engines is DMflywheel/clutch.
In ECU maps there is table where main thing in focus is torque.
Limiting torque is imperative.
Cause you have DMF/clutch pairs in only 2 (TWO) "flavors" in Fiat Power Train (FPT).
One around 300 Nm (+/- 30 Nm) and one around 400 Nm.
Bigger one is paired with GM gearbox in Brera's/159.
Limiting torque low down is a good idea, the standard clutch on a 2.4 will cope with about 400nm at the wheels (make your own calculations for at the fly), I ran mine with 313 lb/ft at the wheels (410?nm) and the clutc was straining.
Of coarse the car would shudder low down because of the strain on the box and transmission.
The box on the 10v 2.4 is rated for about 320 nm, yet seems to handle much more, I run 400nm at the wheels, (440? at the fly, 10%,maybe more?) and its OK, 169k miles! but the boost is limited low down to save the transmission.
I had an interesting chat with a german fellow who knows his stuff on cars, I mentioned that my alfa sustains 1.9bar at max revs, he asked where it was measured, I answered just before the intake, he said what does that tell you, it made me think...is the head and intake the weak point, its Ok measuring big boost before the chamber, but is this indicating a weak spot there?
Has anyone had a head off a 2.4 JTD with a view to porting, or looked at the cams, or intake manifold?
Is it here that lies a weak spot?
Does anyone have a head with cam and manifold spare for reasearch?
Theory is well and good, but this fellow has made me think that measuring temps, after the turbo, after the intercooler, in the intake manifold, boost just after the turbo, just before the intake and so on, this is the way to find the weak spots and make good.
The Gt2256 is only a big turbo on a small engine, its not big on a 330d/530d, most likely the weak spot, same on a 270cdi or bigger, but on a 140bhp alfa it has potential, but are we simply uncovering the fact that the alfa weak spot is in fact elsewhere?