Once again from 440 source
Fact #2:
There are SIGNIFICANT differences between blocks in the main bearing saddles and support webbing.
Lets start with "RB" raised deck blocks.
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What you are looking at above is the number 2 main bearing support on a 75 or earlier 440. This is the area that surrounds where the top shell of the main bearings fit into the block, and the supports that lead from this point diagonally up into the block, to the bottom of the cylinders. The thickness of the main support is labeled "A" while the thickness of the metal forming a "shell" around the bearing is labeled "B." These are the two areas that differ considerably among different blocks, and we will focus on measurements of these two areas. Please note that all the measurements we are using in this section are averages off of multiple blocks, to eliminate the possibility of one block having more or less iron used as an irregularity. The "A" measurement typically is between 1.900" and 2 inches. "B" typically measures about .375" (3/8") All 440's cast before '76 and some after will have these main saddle support measurements. This includes ALL 2536430 (1966-72) blocks, ALL 3698830-440 (1973-74) and some 4006630-440 (Late 1975-79) blocks. I have also found 426 Hemis, Max Wedges and even Mopar's megablocks to also use these measurements. Now on to the late model 440 blocks...
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SOME 440's cast in '76 and later have CONSIDERABLY thicker main saddle supports. The only block we have found to have these supports are the 4006630-440 casting #, which was used from late 75 until the end of production in 1979. In case you have heard that 440's were discontinued in 1978, this was for cars only. 440's continued to be offered in trucks and motorhomes all through 1979, and we have had many 440 blocks stamped with the 1979 model year on them.
Shown above is a picture of a 4006630-440 (1978 model) 440 block. The "A" measurement typically is about 3.190". This is about 60% thicker than the early 440 blocks shown above. "B" typically measures about .520", which is still about 40% thicker. The blocks with these thicker supports were not cast during any specific date period. There is no external markings or numbers which show they are different from the other blocks. They DO seem to be more commonly used for truck motors, however just because you have a truck 440 does not mean it will automatically have the thicker main supports. One important fact is that while 4006630-440 casting # blocks are the only blocks we have found to have these thicker supports, not all these blocks will have them. There appears to be no other way to tell if a block has them or not other then actually looking at the supports themselves. Without the crank and rods removed from the block, it is very hard to tell.
Now on to low deck "B" blocks.
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Shown above is a #2 main saddle off of a 1970 model 383. We have found all 71 and earlier low deck "B" blocks (including 361's, etc) to have this type of main saddles. "A" in this case measures between 1.900 and 2 inches, and "B" measures about .350" These are probably the smallest measurements of all the big blocks. Now lets compare this to the 400 blocks below.
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Shown above is a 3614230 (1972-73) 400 block. These are the thickest of any blocks around, bar none. we didn't even bother to mark the "A" dimension because it is so huge it is practically off the map, and the "B" dimension came in at a whopping 1.350! When you compare this to the 383 and 440 pictures above it makes them look like a joke. One important side note however, is that there are some 3614230 blocks that DO NOT have the thick main supports. Before you spend hundreds of dollars to ship that block across the country, make sure it has the thick mains!! Be sure to always measure or at least see a clear picture.
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Moving on, if you can't seem to find the superblock above, a good second choice is shown above; a 1973 400 block, casting #3698630. Notice the main saddle supports are CONSIDERABLY thicker then both the 383 AND the pre-76 440 shown above. "A" in this case measures 3.750" and "B" measures .575! This is close to a quarter inch more metal in the area surrounding the bearing shell, and the support leading up to the cylinder is almost twice as wide! We have found the thickness of "B" to vary slightly, even among blocks with the same casting # cast during the same month of the same year. In this case we have found blocks between .525 and .575, but still worlds above the .350-.375 measurements listed above for 383's and 440's. Combine this with the fact that the cylinders are shorter (since the block deck height is shorter) compared to an RB, and you can see that a 400 block is ABSOLUTELY stronger then any other block made.
But wait, you say. "I know the early 400 blocks are good...I heard the later ones went back to thin supports...." WRONG (well mostly.)
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Shown above is the #2 saddle on a late model (76-78) 400 block, casting #4006530-400. The "B" measurement remains the same as the early 400 block at about .525 -.575, while the "A" goes down to roughly 3.300, making the support only less than half an inch narrower then the early 400 (still almost 90% of the width), and still over 1 1/4 inches wider then 383's and early 440's.
The end result? Pretty ironic. Chrysler famed powerplants that dominated the muscle car era, 383's and 440's have the weakest supports of all, while their "smog" motors, 400's and late model 440's, which couldn't get out of their own way, have blocks that are considerably more reinforced and able to handle much higher power levels.
There is absolutely no physical difference between a block with an HP or HP2 stamp and one without.
