Go to Happiness island with about 10 RPG's. Get up to a two or three star by killing random people/cops. When the helicopters come, take them down with the RPG's and once you have the 4 star, grab a boat (there are fast one's near the peer) and take off. You will outrun them on sea in just a matter of seconds.
The nifty part of this is that you won't ever run into any cops other than air type. So none of those nasty bugger's that run you over when they pull up.