Crankshafts

[69bigblock]

I'm starting to buy parts for my 454 which I'm going to put a d1sc procharger. The motor is still in the car but the only thing I really need to change is the crank,pistons and cam. I've seen alot of different types of forged cranks 5140,4130 and 4340. Which one of the cranks would be more suited for a street/strip car and what are the main difference between them.

[gmachinz]

I'll try to break it down somewhat for ya. All good cranks are really made up of alloy steels. The first two digits in any four-numbered series represents the approximate middle of the carbon range. A 5140 crank for example has a range of say 38 to 42 percent and it takes into account variations in manganese, phosphorous or sulphur,etc. with the same carbon range. The first two digits represents the type of alloy it is. 51 is Chromium @ .80, .88, .93 .95 or 1.00 percent, which increases tensile strength, hardness, hardenability, toughness, resistance to wear and abrasion, resistant to corrosion and scaling at high temps, too. 41 is also Chromium but @ .50, .80 or .95 percent with Molybdenum @ .12, .20 or .30 percent. 43 is Nickel @ 1.83 percent which increases strength and hardness without sacrificing ductility/toughness. It also increases resistance to corrosion/scaling at high temps. when joined with adequate levels of high chromium (stainless) steels. This type of alloy also includes Chromium @ .50or .80 percent and Molybdenum @ .25 percent. Clearly, for any high perf. application, a 5140 alloy is the best way to go but a 4340 alloy steel is the most popular and available. If you need any help or suggestions on cranks, drop me a line at [email protected] - I own my own shop so I can help you with whatever you may need. -Jabin

[Twin_Turbo]

??? 5140 is a lot cheaper (as is 4130) and it's weaker than 4340, 4340 is the strongest forged moly steel available to my knowledge at least.

[gmachinz]

Let me clarify. I guess by "better" I should have said strongest tensile strength than a 4340. Meaning it will handle stress better. The 5140 cranks do not have the other alloying metals like the 4340 which is a "moly" because it has a significant amount of Molybdenum which among strength (hardness, not tensile) it also allows for better machinability-it can be turned or machined easier than a 5140. Chromium is the primary "hard" material used in crankshafts which the higher the %, the stronger it is-albeit at the expense of making it easy to machine, etc. Molybdenum used as an alloying metal with a slightly lower % of Chromium which allows other metals to be alloyed with it to produce varying characteristics like increased scuff resistance and even MORE resistance to scaling and corrosion at higher temps. It really depends on the purpose of the motor being built as to what crank serves the best purpose. An alloyed 4340 crank is the most popular but it is not the "tuffest" crank imo-I'll put it that way-but the extras that are forged in make it worth the money. -Jabin

[69bigblock]

Thanks for the responses. I've notice the price differences between the cranks and the car will mostly be used for the street. I have a 454 in the car now but the only thing I have to change in order to put a procharger on is the cast crank,pistons(12.5comp), and the cam.