Originally Posted by squeech
From the engine manifold or the cat?
I had more trouble removing the bolts at the cat flange than from the engine. The manifold nuts were quite tight from the factory, but I was able to pull them off with a simple 14mm socket and a 6 inch extension, and then by hand after a few turns. The bolts themselves are studs in the engine, and don't come off (but I'm sure you knew that
If anything, you should really only need some WD-40 if they are rusted on or something.
Your statement about the studs is only half right. True, those studs are into the engine block, but they do come out. When I did my header all 6 studs came right out of the engine with the nuts still rusted in place. I ended up just replacing all 6 nuts and studs at the same time.