As far as I know, Chrysler Corp have right to the design of the HEMI engine and only allow certain other makes to use the design/concept (Daimler & Aston Martin I think) I was going write what I had heard and read about the Chrysler HEMI engine but this is easier and probably more accruate.
http://en.wikipedia.org/wiki/Chrysler_Hemi_engine
Theres a bit about the Ford CVH unit too. T'was similar but not the same. Ford got away with this one by making it a overhead cam instead of a pushrod engine.
http://en.wikipedia.org/wiki/Ford_CVH_engine