Both have advantages and disadvantages, but a good motor can be built with either.
Good info with data is in this link Ron knows his stuff and airplane guys are very good with their testing. Conclusion is that a good motor can be built with either wind type.
http://www.rcgroups.com/forums/showt...t=delta+vs+wye
The data in the link posted above this one is a little misleading since they put a delta wind in their motor which it appears it does not work well in. With a good design there is no rpm lag or low effeciency. We have put many motors on the dyno and found very different results. Ineffeciency means heat and it is no secret that all the 3 slot wye wound motors that are currently Roar legal overheat and thermal shutdown. Heat is king and does not lie.
In short for a delta draw a triangle and each line is a motor winding, each corner is a motor wire.
Now draw a Y and again each line is amotor winding and each end is a motor wire. The center point is floating and not connected to the controller.
In a delta the power passes thru one winding. In a Wye the power passes thru 2 windings. In the same design a Y should have lower kv and the delta should draw more current.
However there are many other factors involved. An example is the Novak motors which are wye wound and yet have higher KV than the delta winds offered by other companies. They have adusted the design to have lots of rpm and little torque on the top end.
Tekin Prez