: Implementing the RK-370SD TamTuned motor (Part 45028) provides a significant speed boost over the standard stock motor.
The identifier "" most likely refers to the Tamiya TamTech F1 series , where 40026 is the official part number for the spare wheel rim set and MP4 refers to the iconic McLaren MP4 series model included in that lineup. 40026mp4
As part 40026 is specifically a (2 front, 2 rear), a key performance "feature" involves improving traction and heat dissipation: : Implementing the RK-370SD TamTuned motor (Part 45028)