If I had to guess I'd say "D" stands for delta and "Y" stands for.. star?
It would be just how the winds are hooked up.
Thats right. both types have current going through two coil phases in series, but d winds also have current going through the third coil, in parallel with the other two coils.
Check out my custom converted 8ight:
Sub 7lb, lowest CG of any 1/8 buggy