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Discussion Starter #1 (Edited)
Some of you already know that the 6.1 block has a bore size of 4.055" and cant really go any larger than 4.08" due to cylinder wall thickness. I purchased 5 blocks at an auction a couple years back and this one block stood out as being different. The part number is different, the color is different, the water jackets are actually from a 5.7, but it had 6.1 cast into the side of the block. I sonic tested the block and found that this block could go all the way up to a 4.185" bore and still be considered safe. This was very strange to me so I inquired with a couple of guys in the know about what I had and this was their response.


If that is the block I think it is, it used to be painted black. Of the 6 or so that were made, most were a rough 5.7L bore size with all other features finish-machined to the 6.1L print. Blocks were cast with the 5.7L bores but I thought we stayed with the 6.1L water jacket core and block material. Cam tunnel cores were 6.1L as I recall but we simply deleted the piston jet machining. Also, it seems to me our intent was to put a “P” at the beginning of the casting number, but I may be confusing that with the aluminum block.

Anyway, if this is the block I think it is, it was an early attempt at a heavy duty/race/blower capable block for Mopar with the idea that we might be able to use it in a skunkworx supercharged buzz model. Never went anywhere and they kinda fell off the table when the discussion turned toward the 6.4L variant being conceptualized.


So basically I have come across a 1 of 6 block that is capable of way more than any production 6.1 block out there. We have decided to use a 4.145" bore with a 4.08" stroke to build a 440 that will be able to handle over 1000hp and thats where we sit. Here is a pic of the block.



Sonic tested this block and with a 4.145" bore, here are the results.

Cyl 1: 186/276
Cyl 3: 237/259
Cyl 5: 236/251
Cyl 7: 259/213
Cyl 2: 206/260
Cyl 4: 219/292
Cyl 6: 221/309
Cyl 8: 183/237

First number is top side of bore where intake valve sits. Our tester scans the length of the bore and the thinest spot is what we record. A typical 6.1 block untouched is less than 200 everywhere with a 4.055 bore. Now we can build a 440ci iron block hemi and hit it with a 400 shot of nitrous or 20psi.
 

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Straight Up Beast SON!!!
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Cool info Andy!
 

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Nice!!! thats good stuff!
 

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Discussion Starter #8 (Edited)
Right now its going in one of our shop cars. I dont really want to sell it knowing what it is. The part number doesnt even exist if you ask a dealer.

Here is the part number for a std 6.1 block.




Here is the 1 of 6 block. Would be nice to locate the other 5.
 

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Discussion Starter #9
Block is decked, line honed, bored, and final honed and ready for assembly.



 

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Discussion Starter #11 (Edited)
Sonic tested this block and with a 4.145" bore, here are the results.

Cyl 1: 186/276
Cyl 3: 237/259
Cyl 5: 236/251
Cyl 7: 259/213
Cyl 2: 206/260
Cyl 4: 219/292
Cyl 6: 221/309
Cyl 8: 183/237

First number is top side of bore where intake valve sits. Our tester scans the length of the bore and the thinest spot is what we record. A typical 6.1 block untouched is less than 200 everywhere with a 4.055 bore. Now we can build a 440ci iron block hemi and hit it with a 400 shot of nitrous or 20psi.
 

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Discussion Starter #14 (Edited)
Went ahead and took the bore to 4.150" as I didnt like the taper we were getting with the 4.145" bore. New displacement is 438ci since we also switched to a 4.05" crank and this engine will be going in my Charger along with 22psi.
 
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