[dkozloski]

Heat the bolt with an acetylene torch until it's red hot. It expands but the bolt is restrained by the metal it is screwed into and collapses on itself. When the bolt cools it contracts and loosens. If you twist the head off anyway the answer is a TIG welder. If the bolt is broken off flush with the surface, build it up with the welder until you can weld a nut to it. When it cools put a wrench on it. If you twist it off again, weld a nut on it again. A rusty twisted off bolt is sometimes loosened by smacking it with a very sturdy punch and hammer to drive it down and make something happen inside. Twisted off manifold bolts can sometimes be removed by building up a lump of brass on the bloody stub and grabbing it with vice grips to twist it out. Which of these techniques you use as well as many others depends on the circumstances. I've been cleaning up other peoples messes for 50 years and have a pretty good reputation in the area. The absolute last resort is drilling and "easyouts". 90% of what can happen is bad.