Some good posts on here.
When I was commenting on Billet cranks being used in F1 etc I was making the point of that they can hardly be terrible if they are used in the very top tiers of motorsport!
Moke makes some very good points on the subject and from my own research there really isn't any consensus in the industry as to which is better, the following statements from these crank manufactures highlights this....
Tom Lieb Of Scat:
“A forging is not as strong as billet because the forging process stretches and shears the grain structure. A forging starts out as round bar of metal and gets twisted and turned to make the rod throws. What used to be centerline of the bar is now offset, and the grains get stretched, traumatized, and weakened, although some sections of it are substantially stronger than in a casting. With billet, there are no stress riser areas because the grain structure runs parallel to the length of the entire crank. Forgings are stronger than billet in bolts and axles because the metal isn’t being stretched and sheared. There isn’t a single Top Fuel, Funny Car, Nextel Cup, or F1 team that uses forged cranks, so you have to ask yourself why.”
Dwayne Boes Of Callies
“If the exact same material is used for both, a forging is stronger than billet because the grain flow is upset and relocated. However, it’s much easier to get special alloys in a billet material.”
Judson Massingill Of The SAM:
“Up to 600 to 700 hp, forgings are every bit as good as billet cranks, given adequate journal overlap. However, when you start reducing the overlap with long strokes and small rod journals to reduce bearing speed, billet comes out on top. In our motors, billet lets us get away with less journal overlap.”
With regard to crank dampers I cannot find anywhere any reference that the viscous type was designed for constant high rpm use. When I was enquiring to Kad about their Viscous type that stated it would be suitable for a road or race car. When I explained my spec of car and what it will be used for (fast road) they stated it would be ideal. Also to quote Fluidampr "Superior engine protection, broad range performance and durability are why you will find a viscous damper as original equipment in high quality sports cars and diesel trucks, such as the V10 equipped Audi R8 & Lamborghini Gallardo, and the Ram 6.7L Cummins".
Furthermore the elastomer dampers are tuned to damp a specific frequency, when rotating assembly parts such as the pistons, rods, flywheel or crankshaft are changed, this will cause a change in the assembly’s resonate frequency and may negate the effectiveness of the damper during peak torsional vibration altogether. So a "one size fits all" elastomer damper may not be as effective as first thought.
Whereas with a Viscous Damper, To quote KAD "Due to the way the silicon fluid operates, it is able to tune itself to any instance of torsional vibration which may develop. Thus the engine will run smoothly and power impulses work in phase with the crank rotation and not against it. Engine bearings will last longer, cam drives run quieter. The engine gains from increased performance and greater reliability."
A viscous damper will effectively control destructive torsional vibration through the entire RPM range of the engine, not just a specific range. Viscous dampers aren’t tuned for a specific narrow band frequency. Because the inertia ring can freely rotate through the housing, it isn’t limited by the elasticity of the rubber.
Fluidampr showing HP gains here.
Edited by Orange-Phantom, 14 August 2017 - 09:38 PM.