Depends on your state. Some states require that the original emissions control equipment remain in the factory locations. Others allow you to move things as long as they are not bypassed or defeated. I just got done with my shorty header for my 2001 ES. I was able to get from 19 1/2" (shortest) to 20 1/2" (longest) primary length. It's an exact replacement for the factory manifold. I even made a hookup for the EGR. The only thing I had to move was the engine lifting bracket on the front of the motor and you don't need that until you remove the engine. I'll be installing it later today and I'm going to test drive it.
