SBC Pistons Marked ".080" ???

[Bib_Overalls]

Ran into something tonight that I have never seen before.  I was over at a friend's shop tearing down a 350 Chevy.  This old block had apparently been apart a couple of times.  The crank is marked ".10/.10" and that I understand.  There are two flavors of pistons; one of one kind and seven of another.  And the odd piston is in a sleeved cylinder.  I can figure out what happened there to.  What I don't understand is that all eight pistons are marked ".080".  I've seen the standard oversize markings before; .020, .030, .040, and .060 but never .080.  We did some measuring with a set of calipers and it looks like the cylinders are bored to at least 4.060.  Does the ".080" mark on the pistons mean anything to anyone?  Never heard of a SBC taking that much of an overbore.

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After posting the above I did a search and found a listing on the Summit Racing site for Speed Pro Chevy 5.7L pistons sized "4.080".  Live and learn.  I thought the max was .060.  In any case, this particular motor was burning a little oil and the cylinders, while showing no top ridge, were not uniformly worn.  There were visable patches of cross hatch, like the cylinder walls had moved away from the rings.  I don't think this motor sealed up very well after it's max overbore.  Based on what I have seen tonight, going .080 over is not something I would do or recommend.

[donsrods]

I understand one pitfall to a large overbore is the tendency to run warmer too.  You guys might be better off looking for a more virgin block maybe?


Don

[GPster]

Runs in my mind that in the old days they used to talk about boring 283 1/8" (.125") to make 302s. When they started talking about thin wall castings to save weight they kind oh lost that brag. The sleeve may be thick enough to handle that bore without overheating OR they may have got the sleeve in there crooked and had to bore it that far to get a piston to run straight in it. I don't think I would try to find seven more .080" pistons to make it even. GPster