Piston-head clearance...how close?

How close have you run piston to head clearance? Application is steel rods, flattop pistons, and less than 6500 RPM.
Seems most like to see .035-.040" minimum. I've run one at .035" and never had an issue.
Just curious to see if anyone has run them tighter?

.035 is usually where I draw the line although the piston alloy can also affect it slightly. Todd

Being slightly too close (.030") causes damage not easily detected: closes up the top ring groove and inhibits ring seal.

I saw witness marks on all the outer edges of my old pump gas motor pistons at .035, none after changing it to .040+
The ring lands where fine, no damage but the edges where shiny, no carbon and the same marks on the heads
that motor got shifted at or above 7000 RPM on every run also so

My daily driven 11.3:1cr 360ci runs with 0.029-0.030" P-H clearance.
My fuelsystem limits the engine to somewhere around 5000-5500rpm.

Mine's been good with .040", even with some piston-to-bore clearances looser than I'd prefer. I wouldn't feel comfortable with much less, having seem other engines with witness marks like Cab mentioned when running a tad too close.

Compression height, skirt length, and rod ratio all affect how much extra P-H you need, but .040" is pretty much safe in everything.
Jenkins said 40 years ago don't run closer than you need for knock suppression - any closer = pumping loss. Some engines with small bores and excellent swirl can be knock-protected at .060".

The 408 motor I just built for my Barracuda is 0.033 (piston is 0.005 out of the hole). Just got it running on Saturday, drove straight to the drag strip. Only made 5 passes on it (I lost in rd3). It held together and got me back home....I call that a win, lol. Ran 6.59 in bad air, on the brakes (would have been a 6.58). The car kept getting faster on every pass...even as the air got worse.
Edit: I shift at about 6500.

All the SB Mopar I've raced and help drag race always made more power after 7 to 10 runs or pulls on a engine dyno to seat the rings fully
Once they level off we start to tune for max power