Im looking to get my head cut but I dont know how to perform the squish how is it done?

get two pieces of soft sodder and bend them at 90 degrees, stuff them down the plug hole so the ends go to the edge of the cyl. wall and make sure you are on the sides over the wrist pin turn the engine over until it squashes the sodder. then pull them out and measure . 55 is almost too tight but useable ,if your stock it's probably around 75 to 80 , 65 you can still run 87 octane

DO NOT use acid core