We learned in the last week, courtesy of IHS Automotive, that four cylinder engines are now most popular in the US, powering 43% of light vehicles sold in the first six months of this year. Six years ago, V6s had that sort of share. Blame high fuel prices and federal bureaucrats' proposed 2016 corporate fuel economy edict. This side of the Atlantic, the new 2012 four-pot XF diesel has its origins, at least partly, with government pen-pushers, in our case at the European Union.