But that brings up the question: why would bolting a turbo to an engine change the glide speed?
Directly, it would not, however, fitting a more grunty power plant can allow a higher max gross weight which will in turn lead to a higher (quoted) best glide, 'cos when you're heavier you need to go faster.. which was what I pondered with my first post. The magnitude of the difference seems rather high for such an explanation however.
I do wonder, if, as waldo posted there might be some interesting transposition going on.
Otherwise, I haven't a clue.