Lower the packer to loosen, raise the packer to tighten. Lower the stagger to tighten, raise the stagger to loosen. Wheel spacing is also a good option. Adjusting these setups will not give you any more speed. Adjust for comfort only.
If you want to adjust the cross weight in the car, read this brief tutorial on Sprint Car cross weight adjustment. In general, more cross weight will tighten the car and of course less cross weight will loosen the car.