Correct, sorry for the mis-info. In all my cars, I installed a knock sensor in the drain holes, from a 85-95 Chevy V-8 (as GM did). Fits directly in the SB & BB drain, needed a 1/4 to 3/8 NPT bushing for my slant. The GM knock module can send a "I'm knocking" signal to an engine controller (ex. Holley Commander 950), which retards the spark.
