This is an optional Exotek B6.1/T6.1/SC6.1 Laydown/Back Motor Plate. This customized polished black base with blue chamfered accents goes great with your stock plastic parts or after market blue parts.
The black motor plate helps reduce your motor temps while the built in gear cover is stronger than the stock plastic cover to insure that the body does not press the cover onto the spur gear in hard tumbles.
Also, the alloy material is kept in place around the motor and bolt screws to resist excess motor plate flex or bending but machined out elsewhere to reduce its weight to 12gr each.
Lastly, the backside spacers are machined into the plate to provide more secure mounting to the gearbox.