I was tuning a 318 in a Astro, COE. The shop I was in, you could not tilt the cab up much because of the low ceiling. I was laying on top of the blower with the governor torn apart, setting the gap on the governor spring when it took off. Got up to about 3500rpm before I could get the air shut off with my shirt, with me in it. Saw one take off one time with a broken air shut off, cut the fuel to it, it ran on the oil in the pan until it grenaded. I would guess about 6000rpm, sounded like a big electric motor, until it blew, then it sounded like a paint can half full of rocks.