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By Tim Quinn - 4 Years Ago
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The aluminum pistons in my '56 Ford say .90. It has all the markings of a 312, ECZ Crank, heads etc.
Question: Can a 312 be bored out .90 or is it a 272 or 292 bored out .90 with ECZ parts added ?
Let me know what you think,
PS: At first we thought it was bored out .60 but the top of the piston says .90 not .60.
Thanks for you input,
Tim,
Central Florida
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By Hoosier Hurricane - 4 Years Ago
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You must measure either the bore or the pistons and see if it is really .090 oversize. I assume you mean .090, not .900. No Y block could be bored .900, that's almost an inch. I would think that it is really .060 oversize, .060 upside down would read .090. A 272 or 292 could go .090 oversize, but a 312 most likely would not.
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By Tim Quinn - 4 Years Ago
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You be correct..................me had senior moment. It is .090
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By 2721955meteor - 4 Years Ago
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hit water boring a 292 to .040, on the back 2 cylinders. put 2 sleeves in,rest ok.be careful on oversize,especially blocks from southern arias that never saw any freez. back 2 cylinders 4 and 8 wher water goes up and threw the heads. i would not use a block that hade by pass hose blocked or restricted as cavitation will erode 4and 8 swell as front cover
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By Joe-JDC - 4 Years Ago
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There are folks who swear they have gone +.125" on a 312, and still running fine. A sonic check would be advisable if you are considering freshening the engine before any major expense for pistons, boring, etc.. My 292, 2018 EMC block is bored +.112, and it had several dyno pulls at 595 hp level. Joe-JDC
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By Florida_Phil - 4 Years Ago
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My 292 block is bored .060. I had it tested before we bored it. It does not run hot or otherwise do anything it's not suppose to. Before I bored it .090, I would find another set of pistons. I am not trying to get the last HP from my motor. Reliability is important to me as I drive on the street. Others may feel differently.
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By darrell - 4 Years Ago
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i have a friend who bored 2 312s back in the 60s 3 15/16 and run one on stock car track.one engine cracked one cylinder and was sleeved.the one on the track never cracked.said he could run away from 327s.
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By famdoc3 - 4 Years Ago
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I’m currently running .080 over 312 in a 56 Merc block for the last few years with no problems. Had been .060 over for 35 years. Sonic checked first and then bored it. No over heating problems just runs good and reliable. Would do it again if necessary after sonic checking if the water jackets weren’t too rusty. Mike
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By NoShortcuts - 4 Years Ago
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Vintage - from back-in-the-day - N.O.S. Jahn's 3.875 inch flat top cast aluminum y-block pistons.
Click the link below to see the seller's ad on eBay . . .
https://www.ebay.com/itm/NOS-312-FORD-Y-BLOCK-JAHNS-PISTONS-WITH-RINGS-PIN-LOCKS-3-7-8-3-875/273807423775?hash=item3fc031b91f:g:YFoAAOSwVKhcs~Zg
Notice the thickness of the skirts on these things! 
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By Lord Gaga - 4 Years Ago
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I ran a set of 3.875" Jahns pistons like those but with 5/8" domes in a '57 Merc 312 in my Tudor back in the days when Sunoco 260 was cheap and street racing was the deal. I was using unposted G heads with the combustion chambers opened up a little, I don't remember the CCs. (I was not aware of posted heads at the time). I used Fitzgerald "Big Bore" steel shim head gaskets. Was driving about 65 MPH on the highway one day and when I mashed it, a head gasket blew BIG time. It was scary!
I had no other problems with that overbore though and block was not 'sonic checked'. Who ever heard of such a thing back then?? LOL
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By NoShortcuts - 4 Years Ago
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Lord Gaga. I had an acquaintance who had a set of Jahns pistons in his y-block back in the mid '60s. I remember his having significant piston slap when he started the engine up cold 'til the engine warmed-up.
I'm wondering what skirt clearance was used back then for fitting Jahns pistons in the bore? My question stems from seeing the amount of material in the skirts of the pistons pictured on eBay. 
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