Finally, my first 360 and goals for it! I'll be asking a lot of questions.

stixx said
No, a standard piston for a 4" bore should be good. The piston will actually be a bit smaller of course than your bore (which is what YR is asking for), that is what determines your clearance. Mostly when buying pistons only the bore diameter is given, but the piston usually is bore minus clearance.
With your little wear even a slightly oversized piston would be too big and require boring or honing on cnc equipment. That is why YR states to just dingle berry hone it (which is honing with an electric drill and, err, the dingle berry hone).

Anybody feel free to correct me.

^^^^^^^^^This^^^^^^^^^

The minimum clearance is designed into the piston, so the stated piston size is nominal, as "in name only".

On most forged Pistons today, for a nominal size of 4.030 the piston will probably measure 4.026-4.027 so finishing your bore at 4.0300 will give you .003-.004 clearance.

Also, in terms of percentages, if your piston is designed for .002 clearance, and you give it .003, you've just given yourself a 50% increase in piston to wall clearance. If you give it .004, that's a 100% increase.

Think in terms of percentages. That's why honing to four places after the decimal is important. And extra .0005-.0008 can be a pretty sizable increase in clearance, as a percentage of what the piston was designed to run.

Filled blocks, real race blocks and power adders will need more clearance.

Learning is fun. Just try not to make it expensive.