How big motor ?

[suicideneil]

1/5 scale conversion & cheap are not two words that go together...

With a little bit of maths, you need to figure out two things:

Select a motor that spins at about 20-25,000rpms on your desired voltage
Select a motor that produces about 4-5 horse power on your desired voltage.

You will also need a suitable esc that can handle the large voltages.

There are a few 1/5 scale conversion threads around, so enjoy the reading...