LS-1's have piston slap from the factory,so did some LT-1's.
It won't hurt a thing,just annoying. Some of the noise will go away after the ring's get a little wear on them.

 

What Arnie said.

Rich

 

The higher the expansion rate of the aluminum used in the manufacture of the piston, the higher the likelihood of noise at cold startup. As noted, JE's 2618 piston has a higher expansion rate. For THAT piston it would be more likely to experience piston slap. Is the slap gonna cause damage to THAT piston? With care until engine is hot, no.

A low expansion rate forged piston, without allowances for power adders, such as the 4032 aluminum SRP, or even lower, an OEM cast or hypertech piston will make for the quietest engine at cold startup. Have OEM assembled engines with cast pistons ever experienced slap? Sure. Were these engines assembled with the proper/correct clearance? No way. Just cuz GM built these engines does not, nor should it, imply otherwise. I give a damn with the GM service manager will tell you, to the contrary. OEM engines of today, as they were 30-40 years ago, are designed to be built within certain tolerances. Sometimes, components and their assembly specs stray outside the tolerance range. Will these engines survive? With care, yes.

The piston keeps the rings stable, and the rings help stablize the piston. However, the more the unstable the piston is, the more abnormal wear the rings will endure. That is NOT good or desired. The rings' intended function/purpose is to seal the combustion mixture. The more piston stabilizing they must perform, the greater the likelihood of unintended sacrafice in wear and ring seal.