The following link refers to LS1 and is reassuring to all LS owners and yes to my understanding the LS3's have seen improvements to what is a basic problem to most manufacturers; the links describe this popular forum 'problem noise' repeatedly discussed here and the US (other most likely have better info but I hope this info helps alleviate some concerns - I personally find just letting the car idle in the garage for a short time (couple of minutes) before driving off helps to quickly stop this driving cold noise than just driving slowly for a few minutes. I am not a mechanic, now only use 95 or 98octane fuel to reduce knock. I don't race the car so use the oil the manufacturer recommends (another popular forum topic) - Delco 1 5W30 oil and I prefer not to go thicker as there are more parts in the engine to consider than just catering for a few minutes of piston clearance chatter.
https://ls1tech.com/forums/generati...791-piston-slap-explaination-gm-engineer.html
SS Forum
http://www.ssforums.com/forum/engine-technical-discussion/63498-piston-slap.html
AMW SS forum member provided this opinion: Okay, what worries me is that some of you don't have any "slap" in the morning, upon cold start-ups. However, I found this quote online from a GM engineer: The noise is an annoyance but will not hurt anything and the engine is fine. (see link for full comments).
Also re "Especially in cold weather starts, isn't piston slap *expected* and *unavoidable* in engines such as LS3 with hypereutectic pistons?
The whole point of hypereutectic is to increase the thermal stability...which is to say to REDUCE the coefficient of thermal expansion. In other words hypereutectic don't expand and contract very much based on temperature."
If you are getting piston slap in an LS3, it can be a worst case scenario of a piston on the smaller side of acceptable tolerance and a cylinder bore on the larger side of acceptable tolerance."
Clearance.
Hope this helps but if not, suggest do a search yourself and lodge any key recognized professional opinions found on this forum. Worth it to ease concerns I also had but are now comfortable with.
In brief as explained in the links above: "Light weight pistons are great but the skirts, by necessity, are short making it hard to make them both strong and flexible and the shorter skirts make them more prone to rocking.
Unfortunately, when the performance and fuel economy oriented pistons are run cold they are very prone to "slap" until they warm up to operating temperature.
The piston designers and development engineers are always treading the fine line between piston slap cold and friction and power/fuel economy loss when the engine is warm."