One-off PWR engine build....

**Motor** · 10-11-2011, 08:54 PM

Here's what Andy posted on one of the other modern mopar sites...

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.