The name "Hemi" carries with it a mystique the real engine is not able to live up to. In olden times, the 426 "Hemi" was the undisputed "king kong" engine. The "new" Hemi is a far cry from that one.
While it is a very powerful engine, the "street Hemi" (426) is not a very good street engine. It only understands one thing. Wide open throttle...
The current "hemi" used in Top Fuel, F/C, etc. is NOT a Chrysler. The deisgn is loosely based on the old 426. One would have a difficult time matching the parts up, as the modern versoins look nothing like the "real" one.
It's true, modern pent-roof chambered, multi-valve heads are capable of making more power, and more efficiently. The Ford modulars are a good examples. A 4.6 lr. engine makes near the power the 5.7 lr. Dodge makes. The GM engines in the same class, make a bunch more power than the Hemi (340 vs. 400).
I believe Chrysler brought the "name" back, along with a modified version of the combustion chamber, to capitalize on the legend. Not unlike the "retro" Mustang...
Jim