The motor diameter has me confused as well... We need some clarification for sure. For a race buggy a 540 diameter (36mm) is plenty. A 720 would be what, 45mm? That's way too much weight for a buggy.
SH Z-Car, Custom Crawler, 8s Savage, 12s XTM XLB 1/7 buggy, 4wd 4-link rear/IFS Pro4 truck, Custom Hyper 10 Short Course, Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz