right before i did my m103 head gasket i took a qt of gunk internal
engine wash and put it in the oil and let it iddle for 5 minutes.... and when i pulled the valve cover then inside of the engine was beauitful...
and when the head was off the rest was clean too....

then i did it on a saab turbo and the turbo went bad... so i think that if you have a turbo and you loosen the garbage up and the soot and coke goes to the turbo it will ruin it....so i think there are some cases when you just need to leave the sludge alone......

so use good judgement.