You can run a 2S lipo in your nitro car, either if you have or don't have high voltage servos. With the HV servos its just a straight connection. However with the 6v servos you will have to use a regulator. Also make sure that your RX pack can handle atleaste 8.40v
The connections with the regulator and non-hv servos would be like:
[2S LIPO] -> ON/OF SWITCH -> Regulator -> rx pack -> servos
The connection with the HV servos would be like:
[2S LIPO] -> ON/OF SWITCH -> rx pack -> servos