well first off you shouldn't be going that fast unless you have at LEAST H rated tires.... GOD I..!!PEOPLE!!
2nd, at 120mph everything happenstwice as fast as it does at 60, and takes approximately 4 times longer to react and stopping distances are increased by about 8-10times
3rd if you get pulled over doing 120mph you will be taken to jail and probably loose your license
Modifying cars is retarded. Buy a bike instead.