Tamiya 56526 TR Torque-Tuned Motor 1/14 R/C Truck Option Parts Series no.26

This low-RPM, high-torque motor was designed for use with R/C truck models, providing excellent throttle control throughout lower speed ranges, and still giving plenty of pull when hauling a trailer in top gear.

Ball bearings and limited power consumption mean that you'll experience long drive times.
★Input Voltage: 6.6-7.2V ★RPM (without load): 12,500rpm ★Maximum torque: 3.92mN-m

The official Tamiya R/C Parts Matching List has plenty of information regarding chassis compatible with Tamiya Spare and Hop-Up Option parts.