What motor???

[BrianG]

Define "a lot of speed" because that makes a big difference.

Normally, I'd say a Medusa 60, but that would be for typical 35ish mph gearing. If you want high speeds, step up to a Medusa 70 or even 80 motor for the added torque (I'd go with the 80).

Then, just pick the kv that will yield ~35-40krpm at the battery voltage you plan to run for speeds around 50mph.

If this is for speed runs over 60mph, pick a kv that will yield ~45k rpm. Yeah, the rpm is a bit higher than normal, but you may need those rpms.