Many different opinions will exist depending on the type of use the engine will see, As Wrench Turner has posted the general rule is 0.001" to 0.0015" clearance per inch of cyl bore dia for cast pistons including Hypereutectic. Many manufacturers will specify much tighter clearances than this for non racing use, ultimately it is up to you. Typically I use much looser clearances than what the mfg calls for mainly because it is extra insurance against hot seizure and really allows you to run the engine harder without an extended break-in period. There is less friction with looser clearances as well.
If it is going into Mom@Pops grocery getter I would go with the mfg's tighter clearances but if you want high performance safely after a short break-in I would use the 0.001" per inch of bore as a rule, it will eventually wear to this anyway. Remember forged pistons need much more.
<a href="http://www.federal-mogul.com/sealedpower/piston_fitting_sealed_power.html" target="_blank">http://www.federal-mogul.com/sealedpower/piston_fitting_sealed_power.html</a>
<a href="http://www.federal-mogul.com/speedpro/pistons_speed_pro.html" target="_blank">http://www.federal-mogul.com/speedpro/pistons_speed_pro.html</a>
<a href="http://www.kb-silvolite.com/page05.htm" target="_blank">http://www.kb-silvolite.com/page05.htm</a>
<a href="http://www.kb-silvolite.com/speclear.htm" target="_blank">http://www.kb-silvolite.com/speclear.htm</a>
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