Posted for "George Braly" <gwbraly@gami.com>:

 Diesels do the high CR for a couple of reaons.
 
 One, it IS more efficient,  but the returns get meager.
 
 But, more importantly,  they need the high compression to get reliable
auto-ignition (ie primary detonation) - - since they do not have a spark.
 
 Regards,  George

"""
 Does this mean that the only reason diesels are 22:1 is that it takes that
much to get
 the fuel to burn?
"""