Piston ring end gap Hypereutectic Pistons needed?

Being this sounds like a mild engine there are some easy math that works for ring gaps. For the top and second ring in a street engine ring you multiply.004 by the cylinder bore.
For the oil rings you just be sure to have.015 minimum as they don't get as hot as the top two rings and don't expand as much.
In the case of the 5.3 the bore is 3.780 So 3.78 X.004 =.015" ring gap for the top two rings
So, for all of yours a.015 gap will be fine. Now if you were building a higher performance engine with a turbo or supercharger you would use slightly different numbers because they generate more heat in the chamber and the rings expand more due to the higher temperatures. Now if you are buying the rings to fit a stock bore and are not using a file to fit ring, it is likely that they will be set to that number out of the box.

Piston material doesn't matter much for ring gap. The idea behind the hypereutectic piston is that the allow the piston is made from expands less from the heat and can run tighter bore clearance than a common cast or forged piston. They are overkill for a normal street engine though because the same properties that make them suited for race use also means that unlike a cast or forged pistons, they don't expand to fill the bore properly unless they are run hard, so they do heat up. That means you get more piston rattle because they don't expand, and you tend to have more blowby as well for the same reason. I won't use them on a street engine build because of the downsides. Instead, a stock or mild build gets stock type cast, if it's going to be a high output street/strip style engine it will get forged pistons. If it's an all-out fire breather with a good cam, tune, turbo or supercharger I might move to the high silicone content and heat resistance of a HUP piston.

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