3-5k rpm. It makes the car sound nicer and it revs more freely IMHO. Don't put test pipes, buy dynomax 53005 high flow cats and have a muffler shop weld them in. Also delete your AIV and PRVR systems before you install headers it makes the install 100 times easier (less garbage in the way)and YugoBernie has some plugs you will need to do this.