i built a very mild street "440" for a guy, that turned out to be a 413 industrial punched out to 4.32. that thing had SCARY thin cylinder walls. it's still out there melting tires, but he is lucky in most all of his endeavors. i don't have any sonic numbers, i just felt the "thickness" by sticking a pinky into a water jacket hole. compared to a few other blocks i had laying around, it was downright frightening. good luck, is all i can say...