Hi! Ideally I would try and get some ballast under the lipo battery. You can either get some lead or brass sheet to put under there. i would put around 75-100g under there personally, this will help with both the stability of the car, and should weight the car down a bit.
The other option is to cut the springs down a little bit, but I have never had to do this myself.
What size motor is in there? Is it a full 540 size? can you measure the diameter of the motor and let us know? I heavier motor will also push the back of the car down a bit.
