Cast vs Forged Crankshafts

TNFrank · Post by **TNFrank** » Mon Aug 20, 2007 10:05 am

A lot also depends on wether it's cast iron or cast steel.

Post by **Piledriver** » Mon Aug 20, 2007 5:53 pm

Cast doesn't HAVE to suck, it just usually does.

Example:

Dodge SRT4... 101mm stroke, 50mm rod journals (same as 2.0 T4, ~itty-bitty) cast steel crank... These see >400HP++ regularly and are not known for breaking cranks.

IIRC they put out reasonably serious HP from the factory.

Read an article awhile back where one of the major tricks they use to make them live was roll forming the journal fillets rather than just cutting it.

Apparently makes for a very strong, crack resistant crank.

This same techique would probably do wonders for a welded strokers strength as well, or ANY crank for that matter, as it strengthens the weakest area of any crank.

I can pretty much guarantee no cast VW crank has this done to it.
Welded C/W stokers are cheap and plentiful, and if bought from DMS or DPR have a great reputation.

Unkl Ian · Post by **Unkl Ian** » Mon Aug 20, 2007 6:19 pm

Piledriver wrote: Dodge SRT4... 101mm stroke, 50mm rod journals ....

I imagine all the latest 4 cylinder motors have 5 main bearings now.
Which would make life easier on the cranks.

Marty · Post by **Marty** » Mon Aug 20, 2007 7:22 pm

Unkl Ian wrote:
Piledriver wrote: Dodge SRT4... 101mm stroke, 50mm rod journals ....
I imagine all the latest 4 cylinder motors have 5 main bearings now.
Which would make life easier on the cranks.

Yep - including your Subys.

The VW "style" my just have them pretty soon too!

terry cloyd · Post by **terry cloyd** » Mon Aug 20, 2007 8:58 pm

A stock VW crankshaft is made from 1045 forged steel. A Scat crankshaft is made fron E4340 steel. Cast cranks are made from poured steel. Other cranks advertised as being made from 1045 steel were, but they added sulphur during the manufacturing process (sulphur speeds up the machining process= lower cost.

I know ....so what does this mean
Yield Break
1045 forged VW 80K 120K
E4340 forged 122K 144K
Cast 18k 18k and can be as low as 11K
1045 forged/suplhur 33K 75K

terry cloyd · Post by **terry cloyd** » Mon Aug 20, 2007 9:09 pm

Sorry one of the important things about the VW 1045 forged crank has a high yield and a good spread between eyelid and break, or it is flexible. The E4340 crank is very strong but not as flexible.

Csaba · Post by **Csaba** » Tue Aug 21, 2007 11:22 pm

terry cloyd wrote:A stock VW crankshaft is made from 1045 forged steel. A Scat crankshaft is made fron E4340 steel. Cast cranks are made from poured steel. Other cranks advertised as being made from 1045 steel were, but they added sulphur during the manufacturing process (sulphur speeds up the machining process= lower cost.

I know ....so what does this mean
Yield Break
1045 forged VW 80K 120K
E4340 forged 122K 144K
Cast 18k 18k and can be as low as 11K
1045 forged/suplhur 33K 75K

The yield strength is the value where plastic deformation occurs when the material is (i am assuming) subjected to tensile force. Break strength is the value where it ultimately fails. An important factor to consider is the spread between the two numbers. Notice that the cast material shows yield and break at the same value. This is often referred to as a 'brittle' material, which is not suitable for quality crankshaft materials. A more ductile material, such as the 1045 forged, is more suitable, but will be less resistant to bending stresses under load than the 4340 forged. For performance applications, you want a stronger material, with a higher yield strength.

Csaba

terry cloyd · Post by **terry cloyd** » Wed Aug 22, 2007 11:10 am

Csaba wrote:
terry cloyd wrote:A stock VW crankshaft is made from 1045 forged steel. A Scat crankshaft is made fron E4340 steel. Cast cranks are made from poured steel. Other cranks advertised as being made from 1045 steel were, but they added sulphur during the manufacturing process (sulphur speeds up the machining process= lower cost.

I know ....so what does this mean
Yield Break
1045 forged VW 80K 120K
E4340 forged 122K 144K
Cast 18k 18k and can be as low as 11K
1045 forged/suplhur 33K 75K
The yield strength is the value where plastic deformation occurs when the material is (i am assuming) subjected to tensile force. Break strength is the value where it ultimately fails. An important factor to consider is the spread between the two numbers. Notice that the cast material shows yield and break at the same value. This is often referred to as a 'brittle' material, which is not suitable for quality crankshaft materials. A more ductile material, such as the 1045 forged, is more suitable, but will be less resistant to bending stresses under load than the 4340 forged. For performance applications, you want a stronger material, with a higher yield strength.

Csaba

Your right.

The cast crank is like glass and can break anytime. Did you note the forged /suplhur crank is less than VW crank.