Prowler V6

[G. Scott Ponton]

    Nitriding, Tufftriding and Hard Chrome are all used for the same
purpose. Yes they add some minor amount of fatigue strenth but mostly they
are to increase the surface hardness of the journals. A cast iron crank has
nearly twice the surface hardness of forged steel. Nearly all forms of cast
iron,other than some of the more exotic alloys, have a ~ .060 thick hard
"layer" at the surface. I am not sure of the technical aspects that cause
this to happen but it is there.
    The reason for using a forged crank as compared to a cast one is
actually more a matter of "flexability." with a cast crank the material
isn't as flexable as the forged counterpart. When you consider the abuse a
crankshaft takes during engine operation, the constant twist and untwist as
power pulses are applied, it becomes fairly evident why the forged steel
crank tends to "live" longer. Especially when engine speed is taken above
5,000 revs
    I have seen many a forged crank from a heavy duty app with the main
journals worn as much as 1/8 in. This wasn't caused by lack of oil pressure
either as the bearings were not worn to speak of. The only journals I have
ever found torn up on a cast crank have been ones that had either been
turned down more than 0.60 or had been run without sufficient oil pressure.
I run a cast (Nodular high nickel) crank in my Pontiac drag car. It has a
455 with 2 bolt mains and cast rods. Rev limit is set to 6,000 (hold it
there for burn outs about 5 sec). Car weighs 3300 empty and runs 10.97 at
123. Put 1200 passes on the last engine before the block split nearly in
half at the mains. The crank journals didn't have any damage at all other
than where it broke as it came out the bottom of the engine. I have never
torn up a crank since I stopped using ones that had been turned more than
0.40.  Wish I could say the same about the blocks :-))) apparently they
aren't strong enough to make more than 700 hp.


Scott.