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412 Cubic Inch FirePower Hemi Mod?
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Indigo Lucifer
Posted 2019-05-16 11:00 PM (#582214)
Subject: 412 Cubic Inch FirePower Hemi Mod?



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Posts: 18

So my buddy was thinking of boring out a 392 hemi to a 412 Cubic Inch displacement by increasing the bore size to 4.101. Is this possible? Will it Work?
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58coupe
Posted 2019-05-17 12:39 AM (#582217 - in reply to #582214)
Subject: Re: 412 Cubic Inch FirePower Hemi Mod?



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Boring the block 1/10" (.100) is quite a bit. You should have the block sonic checked first to see if there is any core shifting.
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ram300
Posted 2019-05-17 2:41 AM (#582218 - in reply to #582214)
Subject: RE: 412 Cubic Inch FirePower Hemi Mod?



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As far as I know the 392 is notoriously thin walled between cylinder and water jacket and even going out +60 is a big ask.

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60 dart
Posted 2019-05-17 9:35 AM (#582223 - in reply to #582214)
Subject: Re: 412 Cubic Inch FirePower Hemi Mod?



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stolen read ,,,,


https://www.jalopyjournal.com/forum/threads/max-392-bore-size.522418...

Edited by 60 dart 2019-05-17 9:36 AM
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57chizler
Posted 2019-05-17 12:20 PM (#582231 - in reply to #582214)
Subject: RE: 412 Cubic Inch FirePower Hemi Mod?



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"Sonic Test" is the key phrase, without it all discussions are moot.
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Powerflite
Posted 2019-05-17 8:42 PM (#582245 - in reply to #582214)
Subject: Re: 412 Cubic Inch FirePower Hemi Mod?



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I have to disagree with ram300. Boring a 392 .06" over is never a problem, at least I have never seen a problem with it. Going bigger than that requires sonic testing, but is often OK too. I have a 392 block that was sonic tested and bored to .08" over with everything well over 1/8" thick. So it is definitely possible to go bigger as long as you don' t have a lot of core shift. But going .1" over is just dumb if you don't have to, even if you have thick walls. You are just limiting the number of times you can re-bore your motor for no good reason. The 5% extra size isn't going to make a huge difference in power so why do it? You would be much better off getting more power using other methods with a smaller bore. You can actually stroke your motor a little bit by offset grinding the crank to big block chevy rod sizes. I don't remember the amount of stroke increase that this gives, but I would bet it is larger than the 20 cuin that you are aiming for.
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Indigo Lucifer
Posted 2019-05-18 2:16 AM (#582247 - in reply to #582214)
Subject: Re: 412 Cubic Inch FirePower Hemi Mod?



Member

Posts: 18

So it turns out Bear Block Motors now makes a new and improved Cast Iron 392 Hemi Block which can be safely bored out to 4.125 inches.

https://www.dragzine.com/news/theres-a-new-hemi-in-town-bear-block-m...
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mstrug
Posted 2019-05-18 6:06 AM (#582249 - in reply to #582214)
Subject: Re: 412 Cubic Inch FirePower Hemi Mod?



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Just Ford blocks as of now:

http://bearblockmotors.com/
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Powerflite
Posted 2019-05-18 7:14 PM (#582268 - in reply to #582214)
Subject: Re: 412 Cubic Inch FirePower Hemi Mod?



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I don't know what the hold up on those is. I visited a casting house about 2yrs ago where a lot of automotive stuff is made and found that new 392 casting there. So I got to see it in person, but I wonder what is taking them so long to bring it into production.
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Handygun
Posted 2019-05-19 10:19 AM (#582279 - in reply to #582214)
Subject: Re: 412 Cubic Inch FirePower Hemi Mod?


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I would definitely want .180 on the thrust side min.
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wayfarer
Posted 2019-05-19 12:17 PM (#582285 - in reply to #582214)
Subject: Re: 412 Cubic Inch FirePower Hemi Mod?



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The question that I always ask is: "what are you trying to accomplish?"
There is little or no benefit to massive overbores unless you are trying to save a 100 pt resto car. If you need a little
more hp then add a cam and up the c/r and use forged pistons.

If the op and friend feel a 'need' for bigger inches then some crank work is definately the safer route to take.
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