The MSD fixed curve timing computer has a pre-programmed timing curve that eliminates the need for a mechanical advance. When you start the car, the timing computers retard the timing 20 degrees from the set mechanical timing. This provides easy starting and smooth idle. The timing begins to advance when the engine speed reaches 1,000 rpm and continues until 3,000 rpm, when the total timing is reached. They also have a separate high-speed retard circuit that allows you to activate a retard amount via a switch, to retard the timing during times of nitrous or high rpm. The retard amount is adjustable with plug-in modules, and 2, 3, and 4 degree modules are supplied. These units install easily, and can be used on 4, 6, or 8-cylinder engines with an MSD ignition control.