That's my theory, and think I read it somewhere long ago - that the belly pan was to raise engine temps. It makes intuitive sense - box up an engine and the temps are going to rise. 100 degree op temps may well be good for emissions, but the heat can't be good for the engine over the long term. And I've always passed emission tests with flying colors - often at one-third or one-quarter of allowable standard, and feel no ecological guilt over it.