I guess when you say burrs, you are referring to the scallop shaped cuts on the face of the crankshaft. Those are turbo cuts that are meant to better help mix the fuel-air mixture (better atomize the fuel with the air), distribute the incoming charge more readily, and to help vector away some of the charge laterally in relation to the crackshaft centerline.
See my post in this thred: (It is post #5)
http://www.rcuniverse.com/forum/m_51...tm.htm#5196204
I hope this answers your question.