I went through this whole fight a while ago. I tried two different impact wrenches and even overpressured (intentionally) a compressor with no results. The big bar didn't work as the engine mounts fles too much. I ended up buyin a GOOD impact wrench (Ingersoll-Rand) that generates something like 600 ft lbs in reverse. The hammers didn' thit more than a couple of times and that sucker was off.
http://www.northerntool.com/cgi-bin/...3&prmenbr=6970