HKS Big Version Heavy Burnt Tip Exhaust Silencer With Round Face - 9821HKS Big Version Heavy Burnt Tip Exhaust Silencer Muffler Tip with Round Face 9821 The AFT part of a car underbody is where a diffuser is usually located. It works by accelerating the velocity of the airflow underneath the car. The pressure under the car is affected by the Muffler Tip; so that it can expand back to ambient in the diffuser, as the car moves through the air. It uses Bernoullis principle, such that the pressure decreases while the