Hi. Best resolve is knowing what compression you have and contacting your ignition distributor for your unique setup example: MSD ignition, Accel, etc.. However may be either 4 degrees before or after top dead center.. I own a 1990 computer controlled 454SS and self adjusts the timing to make up for discrepancies but is factory set at 4 degrees after top dead center WITH the emissions wire disconnected during the timing adjustment with the timing light gun..