I'm currently trying to take the head off my LS B18. I have my motor sitting on the ground and when I try to loosen the bolts the engine spins and the bolts seem REALLY tight. Even when I have someone hold the motor it'll spin.
Should they be this stuck on?

 

they should be very tight but im not sure of your strength or anything so we cant tell how much force your really putting on it. if you have an impact use it. just replace the bolts. they cant be re-used

 

Yes, they are that hard to break free. I would've suggested to loosen them with the engine still anchored in the engine bay to help hold the engine in place. I dont think you should use an impact unless absolutely necessary. To help get some leverage on loosening those bolts, use a breaker bar or use a pipe and slide it over your rachet handle so you can use more body strength and not rely on arm strength so much.

 

Alright, thanks guys. I can probably get them off with my breaker bar but I wanted to make sure it was normal for them being that tight. I was weary that maybe I would end up breaking the studs

 

You could still possibly break a stud, but thats impossible to predict. I wouldn't worry about that so much though.