Not very effective, 1. The angle you need the diffuser to rise with no turbulence is around 15 degrees. 2. You must have clean air channeled to the diffuser. 3. The diffuser need to start at the lowest rear portion of the car. I had one on my car which i designer properly. It started slightly lower than the exhaust and was flat with the bottom of the car. At the rear of the car i made a piece that extends the rear of the bumper cover a few inches so that the diffuser was only 15 degrees. I removed it because it was really hard to work on the suspension, load the car on the trailer without the fins hitting the ground. Did it make a difference, i couldn't tell because the underside of the car was not paneled in.