Cast vs Steel (Steal) Crank

[mickmate]

The literature I've been reading says a cast iron crank is lighter, obviously cheaper and plenty strong for a street/occasional track motor. If there was a steel one available locally do I need it or just want it. Has anyone suffered crank problems in a crossbolted motor with iron crank?

[SFfiredog]

The debate over forged vs. cast cranks has been waged for years.
In general, a good cast nodular iron is more than adequate for a hot street/track car, and in some cases it is actually better. A cast crank is very rigid and stable. This is an advantage, up to the point that the crank reaches it's maximum stress point. This is where the rigidness becomes a disadvantage. Imagine a dry tree branch. When you attempt to bend it, it is firm, firm, firm, then SNAP, it breaks. Now imagine a green (wet) tree branch. When you attempt to bend it, it gives much easier than the dry branch but it will not snap unless it is REALLY bent. That is why a forged crank can handle more long term stresses, because it gives and flexes slightly when stressed. Aforged crank also slightly absorbs torsional vibrations that will break down a cast crank. Let's take a 427 FE engine for an example. A 390 crank has the same stroke as a 427 and weighs about 17 lbs less. As long as the crank is not over-stressed with big nitrous oxide hits, a superchager or extended high RPMs the 390 cast crank is lighter and more rigid than the 427 steel crank. The really trick Super Stock drag racers use 390 cranks instead of steel 427 cranks because they rev higher and quicker. These motors turn way in the excess of 8000 RPMs but only for 9 or 10 seconds at a time. The best combo for a hot street/track motor would be to use the money you would spend on a steel crank and buy some lightweight aftermarket rods and custom pistons (JE, Weisco, Ross etc.) The lighter weight of these parts would make a cast crank's max stress point move farther up the RPM band. I could go on forever but I think I made my point!
HTH,
Mike

[TheRobb]

Most cast cranks from a name company are usually good to about 500 HP.
Above that, you want a forged crank.

As to the weight lightening, this is a very important thing to consider.

If your weight reduction is 17 pounds, then if you factor in the drivetrain gearing, and your total net reduction is 6 to 1 in first gear, then by lightening your reciprocating mass by 17 lbs, in first gear you get an overall effect or reducing the vehicle hole shot weight by 17x6. (circa 100lbs).
Isnt a 100 lbs worth a tenth of a second?

I think this is how it all works, not sure... either was told about this once or read about it somewhere, in regards to building race engines.

-Robb

[mickmate]

Thanks guys, some good points. A lighter crank would be like a lighter flywheel which is another whole discussion already well covered.
Cheers