CAST CRANK vs. FORGED CRANK

[agro1]

I've heard mixed reviews on both, but the overall consensus seems to be that a cast crank is better, stronger, and can spin to higher revs (safely). Is this true ? Thanks in advance.

NEVER LIFT

[RACER X #99]

NO

[Mr.Fixit]

No, in fact you could not be more incorrect.

[bmalone]

No. its actually the other way around.

Steel crank is more rigid, but that does not necessarily mean better. If you live at 7000 all day maybe a slight advantage. Steel, ostensibly is stronger and can spin higher, but this does not necessarily play out in the real world.

Cast gives a little more. Either one is fine for most applications.

As an example, 427s came w/ steel cranks; other FEs like 428 had cast. I believe all Windsors came w/ cast.

[agro1]

Seems I either got some bad info, or I've just been bad...

[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. A forged crank also slightly absorbs torsional vibrations that will break down a cast crank. Let's take a 427 side-oiler 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

[Mr.Fixit]

The crankshaft is only one piece of the equation. Being able to keep the main caps from walking is even more important. The mass of the con rod and piston assembly determines how much work the crank is trying to do. The material used to make the con rods matters as well. Aluminum softens the blow, but doesn't last. The different grades of steel have their own properties as well. etc

[Fred Douglass]

Mike and Fixit,
Many of us less learned wrenches truly WISH you'd "go on forever"---it's a tremendous learning opportunity!

Keepitup!

[Back in Black]

By keeping to the the facts and the germaine subject of cobras and mechanical technology. I have learned some real goodies from him lately.

Thanks, Fixit!

[bmalone]

Here's a link to a PDF on SCAT's Website explaining the differences in cast, forged, and billet cranks. SCAT

Here's another tidbit from Dave Shoe at the FE Forum about the process for making forged steel cranks. Forged steel