BILLET vs FORGED CRANK?

4.500 stroke KB Olds at 8500 rpm's with 10.9-1 and a 980A at 55%. Can I run a forged Lunati crank in this combo without problem's are is this a Billet only setup? How long could I run either one before I would be asking for trouble? Thank's

 

we used to run a 526 ci with a crower crank shafts back in the early 90s we turn it 8500 rpm , we ran more lead back in them days so we change out the crank after 20 to 25 runs , never a problem.

 

Is a forging from the same material not stronger than a billet!!!

 

It depends, you can get forged billets which should have nearly the same properties as a regular forged, but, most billets are rolled or extruded, not forged. The forged billets I have dealt with were routinely quite mis-shaped so larger material was needed which added to the cost.

 

This is an intersting subject.
I have been led to believe it comes down to grain structure. If a part is machined from a billet block, plate, or round, the grain of the material will have been cross cut at some point in the part and it's integrity compromised.
When a part is forged to shape, the grain structure flows with the shape of the part and finish machining does not produce cross cut sections. This has led me to believe that in our case (rods, cranks) forged parts are superior to billet parts.

Fact or fiction?
Truth or myth?
Hopefully someone with some knowlege can clear this up.

 

You can order raw material, bar stock, plate, etc, with a specified grain flow lay.

As for cross-cutting material, at some point, you will cross-cut the grain flow on any part that is completely machined, that is, no area of the part is left in the as-extruded, as-rolled, as-forged, etc, condition.

Forged rods will have machining performed along the grain flow and against it, face and bore.

Forging tends to compress and align the grain flow in the direction you need the most strength, so forged rods will be stronger, but also heavier.

 

Back to the question, will a billet shaft last longer without cracking? I don't see a problem with the journal surface not being hard enough on a forged crank. I asume the major difference would be strength. I've heard all the pro's and con's about the grain cutting deal. Just don't want to spend an extra grand for no reason.

 

all i can say is i bought into the forged versus billet deal many years ago
bought a forged shaft from a well know manufacture from not far from me (same state)
put 9 passes on it magged it and threw it away,
cracks everywhere
bought a billet KB put many passes on it and it is still good, with no cracks even after throwing the rods out once and having it rechromed, now a spare
so i only buy billets now until some one proves forged are better

[ January 12, 2005, 11:42 PM: Message edited by: john348 ]