how to get the exhaust studs of
 

i want to change my old bad exhaust studs in the cylinder heads,

anyone have some good idea how to get them out, without brake them.

(my heads are loose from engine)

I would start by using multiple applications of a good penetrating oil like PB Blaster over a period of days. Then apply heat from at least a MAP gas torch or small tip acetylene torch around the area of the head where the stud is screwed in and gently try to unscrew the stud. It should go OK but remember - heat is the real trick. Good luck and if they don't come out easily - more heat and patience.

This question was asked and answered yesterday. 2 threads below this one...http://forums.pelicanparts.com/911-engine-rebuilding-forum/454689-loosening-seized-nuts-etc-exhaust-system.html

i saw that tread but it was about the nuts, i want to get the studs of the heads.

i assume it not a good idea to heat the heads to much?
how much heat could they have?

for the nuts i use a acetylene torch

Sorry if that was too harsh.

Welding nuts to the studs wont hurt the heads, I've had good results with that method countless times.