Yeah, that clearance was a little much for heavy-duty hi-RPM usage. I rebuild them to 0.0004"-0.0008" (same for the 350F) clearance.
When the clearance is too large the rings will have less tension to the bores. This can develop into harmonic vibration in the 3-piece oil rings, letting oil slip by: this then applies very high hydraulic pressures to the upper rings. If the top ring isn't chrome, it should be for racing - at least, that's how I built the racers I did. I don't do them anymore, though...
...although I still use the small bore clearances. They work fine on the street, too.
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