Which U2? The original Lux version or the current Seoul P4 version?
I have the P4 version and have measured 915mA drive current on high. The tail current draw was about 0.7A with 2x123A, consistent with 2h run time.
Referencing the P4 datasheet, T bin might deliver about 180-200 emitter lumens at 915mA drive current. A U bin P4 might range from 200-230 emitter lumens. Subtracting 20% for reflector/optical losses gives about 140-160 OTF lumens for T bin and 160-180 OTF lumens for U bin.
If you are going to do an MC-E swap, you'll probably want to do it with the Lux version of the U2 if you plan to wire the MC-E in 2S2P. However, since I don't have a U2 Lux version, I can't tell you what the heat sink looks like inside and what might need to be done to fit the MC-E. I can tell you that the U2 P4 version uses two centering ribs to hold the P4 in place. So you'd probably have to grind off those ribs to fit an MC-E for the U2 P4 version and wire the LED in 4P. For both U2 versions, you'll most likely need a shim to raise up the MC-E to the right focus height.
For an XP-G swap in a U2 P4 version, an XP-G on a 10mm diam, 2mm thick MCPCB puts the LED die at the right focus height. So no shimming necessary. You can either trim the soft aluminum MCPCB to fit between the centering ribs or grind off the ribs. If you grind off the ribs, you may have to do some re-working of how the vertical support/LED+ and LED- "struts" are soldered to the heat sink since the 10mm diam MCPCB will overlap the solder pads.
See this thread for some
detailed photos.
