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Original Message
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| All FE cast cranks use the same nodular iron. |
| By Dave Shoe - 12/18/2003 10:13:11 AM; IP 216.243.176.34 |
The 427 cast iron crank used in 1963 and early 1964 NASCAR racing was cast from the same exact alloy as every other FE cast iron crankshaft. The 390 is only different in the balance specification.
Magnaflux the crank, make sure the fillets are sufficient to prevent stress risers (standard concerns for all cast cranks), and race away.
Ford invented the cast nodular crank back in 1951. Nodular iron was invented back in 1947, but Ford tweaked the alloy until the friction bearing surfaces were just right. Crankshaft-grade cast iron is always just about the same, a pearlite-dominant alloy with about an 80KPSI tensile, 60-65KPSI yeild, and 3-10KPSI elongation spec, depending on the specific grade selected.
There is no such thing as a gray iron crankshaft. They just aren't strong enough.
Since iron contains roughly 15% carbon by volume (4% by weight), it also weighs about 10% less than forged steel, making it a favorite among top drag racers and road racers who wish to shave pounds to gain competitive advantage without resorting to super-expensively machined lightweight steel cranks.
The carbon in cast iron also makes it about 10% easier to flex than steel, but this is quite nominal, as titanium flexes about 90% more than steel and aluminum flexes about 240% more than steel for a given loading. HArdening has no effect on flex modulus, so don't be fooled by advertising that suggests otherwise. Hardening principally improves wear resistance, but secondarily can sometimes improve tensile strength at the cost of losing fatigue resistance.
One thing to consider is you must inspect cast iron cranks more often than steel, as nodular iron does fatigue a bit more quickly. Basically, steel doesn't fatigue much at all in these applications, but nodular iron can start to develop cracks over useage, particularly if fillets aren't properly prepared. Having said this, we're comparing the values of gold and platinum, and both are great crankshaft materials.
Not also that all modern cranks advertised as "cast steel" are really nodular iron. It's a bit unscrupulous, but the aftermarket manufacturers are mainly interested in making their cranks sound better, so they can sell more while pumping the price.
Have fun. The 390 crank is actually stiffer and stronger than the 428 crank, since it's got more overlap at the throws. It's perfect for a Cobra car that is properly maintained and inspected.
JMO,
Shoe. |
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