Better late than never... Always too much to do. So, today, with the Christmas Eve, I give you my thoughts.
As for your English, it is much better than for me to attempt le français! It seems many from your country agree, especially when we TRY to speak le français! Heh...so, I won't.
The PD engines have many variants, but the 8v are virtually identical cylinder head castings with few differences. In the U.S., we have one BEW PD with flat-topped pistons and valves that recess. I do not know if there is a European clone to the BEW. The BEW valves are .5mm shorter for both Exhaust and Intake, compared to virtually all other PD cylinder heads, where valves project. The seats on the BEW appear to simply be cut deeper, recessing about .5mm. All others I am aware of, there are valve pockets in the pistons and valves project. The other difference are the blocks that have 81mm pistons require a larger head gasket cylinder hole, but even then, they are not a different cylinder head. Everything is the same except the head gasket to fit around the larger pistons.
As a side note, I think the BEW swirl chamber is more effective and efficient because of the flat-topped pistons.
The real differences between PD cylinder heads are what accessories are installed, as follows:
The valve lobe, intake and exhaust for all our American versions are identical. I understand there are some versions of European cams that have some overlap, which I am not sure I understand, but the big problem we find in all PD cam lobe designs are a solid lifter profile, which is very hard on hydraulic lifters. In our design, we reprofile with a hydraulic ramp, which greatly improves life-expectancy of the cam and lifters.
Cams have several variations for the injector lobe mechanical pilot pop and total lift. Even there, I think this can be a problem, as increasing lobe height increases pressure on an already over-loaded cam journal. The tallest injector lobe height we have seen is in the BRM, which I think is to increase atomization and reduce emissions for the US market. It's driving the smaller pistoned 7mm injectors. I liken the results similar to the 11mm rotary injection pump which are installed in the AHU and ALH automatic transmission cars, with tiny Bosch 658 nozzles. I truly understand why it is done that way. I just speculate.
Injectors, there are a lot of numbers, but not that many 'sizes'. Mostly, I think you can divide nozzles into three categories; Small, Medium and Large.
Lots of 'performance packages' are sold to increase power; some to over 200 or even 300 hp. After seeing many cylinder heads driven to destruction by over-powering them, our opinion is to consider the cylinder head fragile, especially between the injector bores and the intake seats. Most typically, a crack forms from the intake seat to the injector bore, that can advance all the way to the injector's seat, destroying the cylinder head. We are considering some solutions to that vexing problem.
There are many variations on nozzles and even more upgrades on nozzles that should only be done after careful consideration. A stock nozzle can often be driven well enough to provide a lot more fuel without overdriving the chipsets in the ECU or the limits of the cylinder head itself. If additional power is desired, tuning with existing nozzles should be attempted prior to dropping large dollars into upgrade injectors that will sacrifice your fuel economy for excessive horsepower. It seems all the upgrade injector nozzles are performed 'exchange', so once you commit, it may be a mistake that is hard to recover from.
I will also repeat...If injectors bodies are removed for any duration, store them in a container large enough to cover with diesel until they are to be reinstalled. The solenoids are subject to sticking and then it requires expensive, specialized equipment to restore them or rebuild them.
There are plenty of different ECU's in a variety of factory installations; everything from 100hp to 170hp 8v, that I know of. I wonder if some might simply tune out the immobilizer function and give it a try. This, along with the proper nozzles and lobe height and shape, can be massive improvements or massive destruction. The window for injection is to say the least, tricky business. Work with a tuner you can trust.
In the Spirit of Christmas, I wish you all a great holiday.
Peace on Earth. Good will to all.