The material in a sleeve is generally better than the iron a block is made of. They come in 1/8" and 3/32" wall thickness. The thinner 3/32" sleeve is for saving blocks with gouged cylinders where you wish to keep a dry installation ( where you don't wnat to break through the water jacket). The thicker on is for a wet application, although a dry installation can sometimes be achieved. The 1/8" wall is equivalent of about .200 thick cast iron. The structural rigidity is weakened some. The cylinders basically connect the deck to the bottom of the block. When you torque the head after installing a sleeve you will often hear strange noises like cracking and popping as things shift around under stress. Some guys go as far as wet sleeving all the cylinders to get a larger bore size but the block is weakened substantially. You also run a good risk of an internal water leak with a wet installation.
