Exhaust Manifold Bolts

[method]

I've received the advice to use an impact wrench since it's supposedly less aggressive on the bolts than using a wrench. I managed to break 8 out of 12 bolts but then I didn't use enough penetrating oil and/or heat and used wrenches.
If you have a map gas burner I'd suggest you use it to heat the bolts, thus hopefully breaking the bond between bolt and head.