340 or 360?

19DART66 said

But my point being is in 79 when the X block came out the 340 was long gone. So it was my understanding that the X block was based off the 79 318 block that was reinforce with thicker decks, thicker webbing, thicker bores, and higher nickel cast iron casting. That is something that been stuck in my head from something I read about the block back in the early 80's.

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That’s because Chrysler was using over the counter TA blocks for race blocks. By the time 1975-1976 rolled around the TA block was not capable of handling the power they were making back then. So they developed the X block on what was failing on the TA block. That’s one reason why Chrysler didn’t use splayed caps on the X or the R blocks. You can only get a 3/8 bolt and maybe you can squeeze a 7/16 bolt in there. So they used straight bolts with 1/2 threads and stood them up. That moves the bolt center line out. And it’s stronger than a splayed cap with even a 7/16 bolt.

The R block was developed from what was failing on the X block. With the proliferation of 4 inch and longer strokes today, the long deck height of the SBM would be the engine of choice IF could actually get cylinder heads.

In austrialian Pro Stock the SBM is king, but for some reason they aren’t using Ritter blocks (they may be now but not the last time I checked they were scouring the globe for R blocks) and head castings are getting impossible to find.