would you want all nuts and bolts/studs on hand if doing manifold change diy in your home garage if you need to do the job in 1 hit without waiting for parts?
shearing expected on the turbo to mani but low chance mani to head?

 

yeah the turbo to mani bolts often end up gulled and seized, the Mani to head is normally fine. I would make sure you hit them with pb blaster a few times before you try to break them free. Its a good idea to to squirt um up and let the PB soak in over night.

 

Depends on how long your manifold has been on and if anything is rusted or seized. If your car has a good amount of miles on it and your taking of the O2 housing as well for example, you might snap some. Of course like the dude above said use some PB blaster and let it sit. You can even break out the blow torch to heat it up when ready to take it off. If your just taking your manifold off you can probably reuse the nuts. I used a new set but I'm OCD