I had a chance to talk to the piston ring guru at Hastings. Published specifications for end gaps may be too low for current use. Here are some updated notes from our conversation regarding a cherry 360 rebuild:

1) There are no .005 oversize rings available for the 4.05 FE 360, except in aftermarket performance pistons. These use different ring widths than stock, and so are not a direct replacement for original pistons and rings.

2) Brand new, OEMs are shooting for top compression ring gaps of .012 to .022 in similar bores.

3) A wear of .001 in the bore gives a corresponding increase in piston ring gap of .003, in this range of bore.

4) OEMs are finding and recommending larger gaps in the second ring (scraper ring) than previously, as it improves the sealing of the top ring. GM is recommending .026 -.036 end gaps for this second ring. The second ring is mainly for oil control, not as a compression ring.

5) Perfect Circle has a note in their catalog that ring gaps of .040 PLUS the minimum (0.012) are acceptable in practice, and have few drawbacks. This gives an end gap of .052 for us FE folks.

6) End gap is nowhere near as critical as it was in the past because of better technology in the ring manufacturing process.

7) Hot-rodding around on today's rings won't hurt them.

8) Gapless rings are a difference in price of of about $300, and are not thought to be cost-effective for street use.

9) .0035 cylinder taper is on the upper end of the scale

10) My endgaps of .030+ are neither a point of worry, nor cause to expend extra effort for file-to-fit rings.

11) Changing oil more often really does help. (Highway miles are the easiest on oil, and it can go 8,000 miles if not towing, etc.)

Other things from my reading and other's opinions:

A) Get a real endgap filing tool if you are going to "file-to-fit". Don't try to file with a flat file. Hand filing causes long-term problems.

B) With OEMs recommending thermostats in the 195 to 205 range, endgap needs to be larger to follow the slight increase in expansion.

C) If I had it to do over again, I would have had the machinist bore .010 over, and put in new pistons, even with the nearly perfect cylinders, just so I could tighten up the clearances. It would have been about $200 more. But I have the advantage of matched parts at this point, altered only by the hone job.

D) A looser fit makes for easier starting in winter

E) Low-octane gas may result in HIGHER TEMPERATURES and pressures, due to more borderline pinging conditions. Alcohol in gas will help.

Factual comments welcome.

 

Piston ring end gaps are indeed critical. Some of the early failures of hypereutectic pistons were possibly from overly close ring end gaps.
Ring end gaps will also vary with intended use.
High performance street/strip use will dictate a more generous gap especially on the second ring.
If you are planning on a spray of NOS, factor that into your clearances also.
Best bet is to forget the old school numbers in the Chilton book and follow the piston/piston ring manufacturers recommendation. If the specs are conflicting, lean toward the larger of the two.
Squido