the cv-r has been designed specifically for off road buggies, it has beefier bearings & a thicker crank. it can handle all the bumps & hits you get with off road. the tz is designed for onroad, not as sturdy, but will be more powerfull. i find the OS 15cv-rx has plenty of power for my evader & my next engine will be the OS 12 cv-r. i personally wouldn't spend my money on the TZ, i'd get the OS12 cv-r. all you'll end up doing with the tz is spend time fixing worn & broken parts.