Fred has clarified that the 17.5 is just for nationals and the 21.5 is still the standard motor for 2026 regionals. The choice of 17.5 for nats is due to the long straight at SCOR.
The 21.5 is too slow for Jackson. Big Dog is huge too. Should be 17.5 on large outdoor tracks and 21.5 on indoor carpet. With the weight and motor timing spec at 180 Raceway earlier this year the 21.5 was slower than what we were used too but it was still fun as the track is only 80 x 34 but super high bite on the black CRC carpet.