yep i had a 509 block ran it for 2 years had cometic gaskets on it always thought they leaked some over night... so i just drained the radiator after racing and went on with it ... then i had to take engine apart one day and found i had a hair line crack in one of the cylinder walls toward the lifter bores... it was about 3 inchs long... u could barely even see it ...been runnin it like that for 2 years .lol thank god it wasnt on the thrust side.. prolly tore up everything heck i ran compression and all on this engine many times and it was fine... i have had many 350 block crack and u can tell when they did be a wide crack...