i was very curious about this. having supercharged other cars; i always picked up knock from the rotors and zeroed the knock tables but i am not an expert with the new coyote platforms so im unaware of the knock strategy and effectiveness. given that i use 91 (my kit must remain pretty smog legal(ish)
) i still need to log knock somehow other than my ear so ill have a look at the plugs as you mentioned. i've had very bad experiences with little amounts of knock and OEM subaru pistons so i am very cautious.