Eagle offers several different varieties of crankshafts to fit almost any application. Eagle cast steel cranks are cast from carbon steel, but they are not 4340 alloy. They are intended to be a viable alternative to reworking an O.E. crank. Minor design changes often result in a slight improvement in strength vs. O.E., but they are not intended for competition use. Eagle generally recommends our cast cranks for use up to 500hp in a small block and 700hp in a big block.
Eagle forged 4140 steel cranks fill the gap between the O.E.-replacement cast cranks and the all-out competition 4340 steel cranks. The design is identical to the 4340 steel cranks, but by using the greatly less-expensive 4140 alloy steel, we are able to really keep the costs low. 4140 steel is not slouch, it is still a chromium-molybdenum alloy, it just lacks the nickel content of 4340 steel. The difference in strength is about 22%. You can save quite a bit of money using a 4140 steel crank, so if your application is right, forged 4140 steel is the way to go. Eagle recommends our 4140 steel cranks to about 1200hp in most applications.
Eagle has several different variations of 4340 steel crankshafts. For short-run production, we are now offering billet 4340 steel cranks where the costs of a forging are not viable for the quantities we produce. "Billet" has the reputation as being the strongest available, but the truth is, with all other variables being the same, a forging is stronger, but only marginally. Billet is utilized for custom or short-run production. Dedicated forgings are expensive! Eagle can justify forging costs for many common applications. We have to produce a lot of them, but thankfully, the enthusiast and motorsports industry is large enough to justify such production. Eagle 4340 steel cranks are all nitrided to provide a very hard surface for superior wear resistance. A .125" fillet radius is used on all journals to greatly improve rigidity and strength so narrowed or chamfered bearings must be used. Eagle also offers several cranks with a center-counterweighted design. The addition of center counterweights may add weight, it also provides for greatly improved stability at high rpm and high power applications. Eagle forged 4340 steel certer-counterweighted cranks are the strongest production crank you can buy. We have seen them used in engines approaching 2000hp depending on application.