What are the Differences Between the P-1SC and D-1SC Head Units?
The differences between the P-1SC and D-1SC are not many. The housing is the same, the step-up is the same, but the bearings are heavier duty in the D-1SC, I believe. The main difference is the helical impeller in the D-1SC, as opposed to the radial impeller in the P-1SC. The helical impeller provides for a sharper boost curve (more boost at lower RPM). The radial impeller in the P-1SC provides a smoother, flatter boost curve and is more appropriate for milder applications and mainly street-driven cars. For stock or mildly modified motors, the D-1SC is quite often unusable because its boost output will be too high for the motor to handle, even with the lowest pulley ratio. ATI generally specifies that the D-1SC is for modified motors only. Depending on the motor and current modifications, if any, you can sometimes use the D-1SC and use a pulley combination that will result in a low enough (and safe enough) boost level. If your motor is modified and you have the option to use either, yo
