what is the advantage of having a block guard. what exactly does it do?

 

from what i understand it prevents the upper part of each cylinder from flexing. It would flex due to upped comp ratio or boost or N02. With reduced flex it prevents blowby past the rings. Im not 100% sure thats how they work but its how i understand it.

 

it restricts coolent throug the water jackets. its not any thing close to getting your motor resleeved.

 

The head gasket has holes basically in the same areas as block guards.

Unless you have an extra $600+ for resleeving, a good block guard is an excellent choice.