Vibrant Performance aluminum bellmouth velocity stacks are constructed from spun, 18 thick T6061 aluminum and are designed with the turbo fabricator in mind. Vibrant Performance bellmouth velocity stacks are ideal for all motor and forced induction race applications. They allow for less turbulent air to enter your engine and reduces turbo lag which cumulates in dramatic airflow improvements resulting in significant torque and horsepower gains. They are available in Inlet O.D. dimensions of 2.5 to 5 and bellmouth O.D. dimensions of 6, 7 and 8 .