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Old 09-16-2003, 04:35 PM
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Default How much overbore can a hemi take?

I heard that hemi blocks were usable until .120 thou over(or could take this much overbore) . Is this true or is someone telling tall tails?
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Old 09-16-2003, 04:54 PM
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Some of the early hemis (331, 354, 392 and the dodges and desotos) can take a pretty hefty cut on the bores, but as with any wild bore job, I would have it sonic tested to find out how much meat is in there. As for the 426 hemi, same thing, but I haven't heard of anyone taking them more than .060 over.
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Old 09-16-2003, 05:15 PM
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The reason I ask is I found a 426 hemi block but it has been bored 90 over (good curret bore). The person that owns it said that it could go 120 over. I was just wondering if this is right or not. I would hate to buy a block and when it came time to rebuild the motor it didn't have any life left in it.
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Old 09-16-2003, 05:17 PM
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Maybe you could ask him if you could take it to a shop and have it sonic tested.
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Old 09-16-2003, 05:21 PM
John Kunkel John Kunkel is offline
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The question is like asking what a chicken weighs. There is no set answer, only a sonic test can tell if a block will accept a major overbpore.
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Old 09-16-2003, 10:48 PM
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120 over? sleeve comes to mind or a low RPM Low $ parts industral engine Just like the post how much does the ckicken weigh? How long is a well rope? How much $ can you Pi$$ off? Sonic test before your $ become his $
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Old 09-17-2003, 02:54 AM
DartGT66 DartGT66 is offline
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Many people are recommending to sonic check blocks before boring them. That's OK, but what good does that make? The thing I have never seen in this kind of conversation is, that how thick wall you should have there after tyhe bore for the block to be good? I think that information is pretty critical.
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Old 09-17-2003, 11:52 AM
mr_340 mr_340 is offline
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Default Wall Thickness

I wouldn't want the walls any thinner than around .200' on the major thrust sides. I know the SS Hemi racers take them out as much as +.070" (per the NHRA rulebook), but they are using block fillers and the replacement blocks. The only Hemi block that can safely be bored out +.120" is the siamesed Hemi block. It's designed to go as big as Ø4.500", but MP recommends sonic checking the block before going that big.

If you can get it cheap enough, then maybe it would be worth putting a sleeve in every hole. You should plan on using a very good machine shop for that process. Or, fill it with block filler and leave about 1" of water around the top and use it only on the strip. Maybe it won't smoke too bad
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