3. Shot Peening - Shot peening involves firing thousands of tiny steel pellets at high velocity at the block. (Note the high-speed blast wheels.) While thermal cleaning will get all of the goo, shot peening will remove surface contamination such as rust, scale, and even some small irregularities in the casting to create a clean and smoother surface finish. More than simple aesthetics, shot peening makes it easier to detect surface and subsurface defects. The same process also acts like mini ball-peen hammers pounding away that the block to impart additional strength through compression.