Early XBs used high impedance side feed injectors driven directly by the ECU.  The 12 Ohm injector used the normal old style injector connector.  The PCI harness was wired such that there were two injectors in parallel on each of the two injector driver lines.  In short, if the injector has a connector on the top, it is an older style high impedance injector.

Later XBs used a PCI amp that was placed between the ECU and the PCI injector ring.  This amp took the two ECU outputs and generated four peak then hold signals to drive a newer Bosch EV10 low impedance (1.2 Ohm) injector.  These peak then hold drivers were included internal to the XD/XF(E) fuel control.  The harness for this style injector is soldered directly to pins protruding from the top of the injector.  There is no connector on the top of the injector.  The newer EV10 injector is also smaller and thus the PCI ring is smaller.  You will find lots of the older style PCI rings in the obsolete spares bins.  Regretfully, the newer style is still used on the XFE and thus not readily available.

With respect to flow, you can expect the older style injectors to flow at least 25% more fuel than the newer EV10 units given the same input.

High Imp. on Left Low on Right Click to Enlarge	High Imp. on Left Low on Right Click to Enlarge