Could someone please explain the difference between cast, nodular and forged cranks. I have a couple engines sitting here and want to build a 383. I have a Targetmaster crate motor that was free and I am thinking this would be a good base for a Vortec stroker.It supposedly has a nodular crank but has a spun rod bearing so I figure if it wont clean up it needs to be stroked. We can get into more details once I figure out what to do crankwise. Thanks in advance.

a cast crank is one where the melted liquid iron metal is poured into a sand casting mold and allowed to cool/harden to a solid state.

a nodular crank is a cast crank that has been sort of heat treated/tempered to surface harden the journals,, sort of,, as a way of describing it. maybe someone else can elaborate more on the nodular iron before i screw that up. but it's a little bit stronger than the plain old cast crank.

a forged crank is a steel material that is poured into a mold/forging die and allowed to almost harden,, but still red hot,,, then pressed with a big forging die into shape. in some cases with like factory cranks the journals are forged in line with each other,, then twisted into position at 90* apart while the metal is still molten red but not hardened yet. the pressing function or forging compacts the molecules of the metal close together/denser to be less porus and have less air pockets microscopicly. much stronger all together overall.

then you have the non-twisted forgings which are a bit stronger still.
then you have the billit forgings that are even stronger yet. they will be fully machined from a billit block of forged steel. big $$$ for those.

Boy, geeze, here we go.

There are gray-iron, cast-iron cranks that GM doesn't use!!

Then there are cast ductile/nodular-iron cranks GM uses!

This grade of iron is treated in inoculating ladles w/ Mg so that the flake graphite/carbon in the iron turn's to about round glob's so that stress-risers due to carbon are really low!! Make's for a tough cast-iron, imho!!

And I've stood next to the innoculating ladles too that are used to make the stuff!!

Next, there are cast-steel cranks.. Try SCAT's site............... Tough, cheap suckers up to a point!! Imho...

Then there are forged cranks in several steel alloy's that are hot forged from a cold billet that's heated to darn near orange hot, then hammered or hydraulically pressed to shape and machined finished! I've seen it done!!

Next is a true machined billet crank that is machined out of a cold slug of hard metal!! I haven't watched this done!!

Plese go over to SCAT's site and look into all the alloy designations they list b/c it is DARN GOOD info on this, you will learn a bunch!!

pdq67

pdq, if I understand you, you are saying that all GM's cast cranks are nodular iron? I did not know that.

One of the reasons forgings are stronger is "grain flow."
When you pour metal into a mold it's grain is horizontal in the mold. The casting is strongest against the grain, but weak with the grain, the same as lumber.
A forging uses many tons of pressure to force a slug of metal into the mold, which aligns the grain. In a crank the grain would be running lengthwise.
The twisted crank forgings reduce the strength where it's been twisted because the grain spirals there. It still runs perpendicular to the forces on the crank, so it is still strong, but there is still a weakness.

Iron is harder than steel. It does not like to bend. Steel will flex. Instead of bending, iron will break.

I am under the impression that for lower power levels iron cranks are more efficient. A forged crank will flex with each ignition cycle, causing you to lose a little power.
Hor higher power levels you need to have a forged crank because the iron crank will break.

So would I be better of with the nodular crank I have if it will clean up? Or a forged GM crank that I can get? Or should I just bite the bullet and buy a Scat stroker crank? This will just be a hot street motor and never see the track.

I think GM through the years have made Chevy nodular-iron cranks and also what they called "ARMA-STEEL" cast-steel for their other Divisions that ran cast rotating assemblies, including rods!

But check me on this.

pdq67