The Cusco Roll Center Adapters (RCA blocks or roll center blocks) do a couple of things. Designed to correct the suspension geometry settings by returning the roll center of the front control arms closer to the stock location after you lower your car. This helps cornering as the weight transfer is better ballanced.
Second is rectifying the bump steer, after you lower your car, the amount of angle on the lower arms and tie rods affect how much change in toe you recive as the car goes through its suspension travel. You may notice it as you corner and hit a bump, the steering will jump or jerk.
By putting the angles back to standard geometry settings, it will lessen the amount of toe change you recieve which will give you a smoother steering feedback.
CUSCO has a brilliant record and history in the top categories of track racing, rallying, dirt trials and gymkhana. By staying continuously in touch with each cars potential and character, they can create settings for almost any car. From this experience in motorsports, they developed confidence in their CUSCO brand for street use. The CARROSSER competition products are developed one by one from their broad and long experience in competing in motorsports, and based on their extensive data and know-how. CUSCO responds to those who appreciate such matters, like driving a car or controlling its performance.