With crank fire you have a 4 x 12 control module. There are three coils mounted on its billet base. There is also a crankshaft pulley with notches around the edge. A magnetic pickup pointer is mounted .50mm from the pulley 's edge. A single wire goes from the pickup to the control module. When the engine is running the coils take turns firing the spark plugs. The pickup fires each cylinder in the proper order. On the control module is an adjusting knob to set the rev limiter, along with three more adjusting knobs that allow you to plot the advance curve. This allows you to use a curve that matches the requirements for a modified engine. Example: your engine has more aggressive camshafts. In order to get the greatest horse power, the engine will need more timing at lower r.p.m. Values. It is a simple matter to turn the adjusting control knobs to a new curve and then do a road test to confirm its effectiveness. There are no moving parts to wear out or replace with the crank fire. The crank fire ignition systems is the most complete systems sold in the Porsche market. Other kits come with only modules and the crank plate and do not supply technical support. Please specify with or without air conditioning.