Just wondering here, goona do a 4x4 318 for a friend and have to buy a oem set of pistons but I have a set of old new oem.

So are the new non hyper, non coated any better or worse then ones from say 1974? Thanks.

I think most would agree that today’s ring choices are superior in less friction and better seal,
and new rings might require new pistons.

I think most would agree that thermally coating oem piston crowns
yields about 1% more peak power and better fuel efficiency.

If the new pistons reduce the quench clearance into the range of 0.026 to 0.33 inches from the crown flats to mating surfaces on the cylinder head there might be 2-4% gains if ignition timing gets re-adjusted too.

Different pistons might require an expensive crankshaft rebalance.

If you are not racing or not having to meet super strict EPA fuel economy fuel economy regs, stay with original.

It doesn't seem "modern oem" is what you're asking about.
"Modern OEM" would be something like a 6.1L Hemi piston with coatings, thin metric rings, light weight and so on.

"Stock Replacement" would seem to be what you're actually looking for information on.

If the specs are the same on the replacement parts as the old ones, they're not any better and they're not any worse.

Both the old and the new will be a great big heavy cast piston with big old 5/64th rings set way down, using a big heavy wrist pin,
no coatings, nothing different happening there.

Do the replacement parts have the same specs as original?

Aren't most stock replacement pistons overcompensated for as far as head and deck resurfacing, offering very low deck clearance and compression?