I did a search here and didn't get a clear answer, so here goes.. I am wondering what the difference is in a Cast, Nodular and Forged crankshaft? I have some of each and I am really interested to know exactly why the nodular is different. I bought a '70 854 cast block motor today for $200. It has the 3963569 intake, dimple rods, 063 heads and forged small dome TRW pistons. It has a Nodular crank also. It appears that the deck got swiped when it was rebuilt. It is +.030" bore. Has a L-4-70 date block. Heads are K of 1969. The previous owner said they removed it from a El Camino SS. So whats up with a Nodular crank?

I did a search here and didn't get a clear answer, so here goes.. I am wondering what the difference is in a Cast, Nodular and Forged crankshaft? I have some of each and I am really interested to know exactly why the nodular is different. I bought a '70 854 cast block motor today for $200. It has the 3963569 intake, dimple rods, 063 heads and forged small dome TRW pistons. It has a Nodular crank also. It appears that the deck got swiped when it was rebuilt. It is +.030" bore. Has a L-4-70 date block. Heads are K of 1969. The previous owner said they removed it from a El Camino SS. So whats up with a Nodular crank?
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Short answer
Nodular Iron is a higher grade of cast iron & has a higher tensile strength
I don't have the numbers offhand but I would bet if you did a Google on Nodular Iron it would come up. ;)

(I did a web search and found a great article from Car Craft's website on types of engine crankshafts...) Happy Reading! Neil...

Crankshaft Materials Explained..
In addition to cast or forged, material quality separates the different grades of crankshafts. What we're interested in is raw strength and durability. Various steels and irons are rated on the basis of strength, toughness, and ductility. Any given alloy can cover quite a wide range of strengths depending upon the metallurgical processes involved, so it is difficult to put an exact number on the strength of various steels and irons. However, to provide a general guide, we'll include some relative tensile strength numbers here. At the bottom of the list is a standard cast-iron production crankshaft, which typically has a tensile strength of 65-80,000 psi, and is fairly brittle with an elongation rating of some 3 percent. Some OE iron cranks were made from nodular (ductile) iron, an improved cast iron that ups the tensile strength into the 100,000-psi range, but more importantly improves ductility to about 5-6 percent elongation before failure. With the popularity of low-cost aftermarket cast cranks, we asked Scat Crankshafts about the material in its budget cast cranks. These cranks are cast with a 9000-series cast-steel material with a tensile strength of 105,000 psi and 6 percentelongation--pretty impressive numbers for a cast piece.

Forged cranks also come in a wide range of materials with varying degrees of strength. A factory-forged crank is typically manufactured from plain carbon steel, such as 1053 or 1045. These steels have a tensile strength in the 110,000-psi range, which by appearances doesn't seem like that much more than a good cast crank. But tensile strength is only one part of the picture. A forged-steel crank has an elongation rating of 20-22 percent before failure--far greater than cast iron, so ductility is the forged crank's real advantage over cast iron. From the OE-grade carbon steels, forged-crank materials go up the scale in strength with 5140 chromium steel being the next common grade at 115,000-psi tensile strength. Chromium molybdenum alloy steels are next up the list, with 4130/4140 steels commonly used for more serious performance crankshafts, at about 120-125,000-psi tensile strength. Premium forged-steel race cranks are manufactured from 4340 nickel chromium molybdenum alloy with about 140,000 psi on the tensile scale.

Billet Cranks
Billet crankshafts are at the top end of the high-performance crankshaft scale. A billet crank starts as a solid chunk of high-grade steel bar (typically 4340 material), and then everything that doesn't look like a crankshaft is whittled away through a series of machining processes. The advantage of billet is primarily in the grain structure. The rolled bar that forms the billet has a uniform longitudinal grain structure. In forging, the crank throws are literally pounded, pressed, and twisted in the dies, mashing the metal into the rough shape of the crank. The brutality of this process adversely affects the grain structure of the metal. In a billet crank, the grain structure of the original bar isn't distorted, and remains much more uniform and intact. This makes for a stronger, stiffer, more durable finished product.

Scat has an excellent write-up on their 9000 cast cranks too if you want to do some more reading!

pdq67

I saw that they had some more info on that same article from Scat. Here's a link to the entire story...

http://www.carcraft.com/techarticles/116_0308_crankshafts_how_to/index.html

A nodualr iron crank is stronger then a std cast iron crank and if the nodular crank is setup/machined/installed properly with no oiling system issues is a good crank for a street/strip pref motor that should be able to handle pretty high perf/hp lvls IMHO.

Scott

MacKenzie in his 1944 Howe Memorial Lecture referred to cast iron as "steel plus graphite."

Gray iron belongs to a family of high-carbon silicon alloys which include malleable and nodular irons. With the exception of magnesium or other nodularizing elements in nodular iron, it is possible through variations in melting and foundry practice to produce all three materials from the same composition.
Source: http://www.ironcasting.org/Gray%20Iron%20-%20A%20Unique%20Material.htm

My understanding--and I'd love to be corrected by someone with real metallurgical data--is that ordinary (white or even grey) cast iron is unsuitable for crankshaft use.

Therefore, any cast iron crank is either malleable iron (sometimes called "Armasteel" which was a GM trade name) or nodular iron (also known as “Ductile Iron”) which was first used—and perhaps patented for crankshaft use--by Ford. I heard that when the patents ran out on Nodular iron for crankshaft use, GM dumped Armasteel and began using the superior nodular iron. Pontiac and Cadillac, for instance, quit bragging up Armasteel internal parts in the early/mid ‘60’s. Chrysler brags up “Pearlitic” iron; but since there’s both pearlitic malleable iron and pearlitic nodular iron; I’m not sure what Chrysler is talking about.

As with so many other things, there's a thousand different "recipes" for making either malleable or nodular iron; then there's the whole issue of post-processing: heat treatment (including cryogenics) and chemical treatments (for instance nitriding) and other finishing processes (polishing and/or shot peening) that can tremendously affect the overall quality and suitability of the finished product.

Don't get me started on Chinese "Cast steel" cranks...except to say that I expect there's about as much "steel" in them as there is in Armasteel. (NONE!)