3s really can't supply enough power. It might work if you geared it for about 30mph, but I'd guess that's as much as you could get out of 3s Lipo. 50mph will take at least 5s Lipo.
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