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I just bought my 392 used last year but my warranty expired. Soon after my valve spring went out and piston knocked the valve into the head and broke the crank bolt. I was thinking of boring the scratch out the block and stroking it with some new bigger heads, but what is the most I can bore the block without making the walls too thin? I have also heard the 6.4 is just a stroked and bored 5.7. Can somebody help me out?
 

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I just bought my 392 used last year but my warranty expired. Soon after my valve spring went out and piston knocked the valve into the head and broke the crank bolt. I was thinking of boring the scratch out the block and stroking it with some new bigger heads, but what is the most I can bore the block without making the walls too thin? I have also heard the 6.4 is just a stroked and bored 5.7. Can somebody help me out?
You probably want this book:

https://www.cartechbooks.com/new-hemi-engines-how-to-build-max-performance.html

There are a number of factors on how much you can take out of the cylinders. One of the biggest is the condition of the block, how true to form is the block casting.

Unless you x-ray the block you can't be sure each cylinder has the same/correct position to know the wall thickness will be uniform and of sufficient thickness.

Generally to be safe, albeit to maybe leave some displacement on the table, but possibly leave some cash in your pocket, the overbore only wants to be enough to clean up the cylinders. Thus a 0.010" overbore would be preferable to a 0.030" overbore, provided of course 10 thousandths of an inch over cleans up the scratch.

A good automotive engine machinist could advise you how much needs to be removed. He might -- if he's done enough of the 6.4l engines -- be able to advise you how big you can go.

But get the book I mentioned above. I believe it should contain info you will find helpful and from the guy who well, wrote the book on hot rodding modern Dodge Hemi engines.
 

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You probably want this book:

https://www.cartechbooks.com/new-hemi-engines-how-to-build-max-performance.html

There are a number of factors on how much you can take out of the cylinders. One of the biggest is the condition of the block, how true to form is the block casting.

Unless you x-ray the block you can't be sure each cylinder has the same/correct position to know the wall thickness will be uniform and of sufficient thickness.

Generally to be safe, albeit to maybe leave some displacement on the table, but possibly leave some cash in your pocket, the overbore only wants to be enough to clean up the cylinders. Thus a 0.010" overbore would be preferable to a 0.030" overbore, provided of course 10 thousandths of an inch over cleans up the scratch.

A good automotive engine machinist could advise you how much needs to be removed. He might -- if he's done enough of the 6.4l engines -- be able to advise you how big you can go.

But get the book I mentioned above. I believe it should contain info you will find helpful and from the guy who well, wrote the book on hot rodding modern Dodge Hemi engines.
What he said^^
And my machinist guy says .020" is the max overbore regardless of what the books say. Things like core shift and vertical drift alignment with the crank also come into play. Modern thin wall castings are there for reasons of economy and production line ease of construction not having to remove as much metal as they did just 30 years ago.
In stock form, the 392 block is strong for it's designed purpose. Start grinding metal off here and there... you are on your own.

-John
 
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