B4Ctom1

What kind of crank do I have? I hear this all the time. Mostly factory cranks are usually of the cast variety. What kind should I use in my buildup? Well this is what I have to say about crankshafts. Starting with factory cast cranks. There are two types of cast factory cranks to my knowledge, "Grey" cast iron, like your blocks or heads, and "Nodular" cast iron, which has a little alloy of some sort (nickel, I believe) to make it stronger (most late model engine blocks have a higher nickel content for same reason and exhibit awesome wear characteristics). A new catchword that we are hearing from Scat and Elgin and a few others is "cast steel" or 80-60-08 cast steel cranks. It is of similar material to forged cranks but it is not formed under tremendous pressures (taking a lot of metal and pressing it into something smaller and stronger). They just pour this steel into forms and add a little alloy change to make it harder. These are a step up from cast iron and will suit most performance needs for hot streetcars and are successful in circle track as crankshafts. Cast Steel cranks offer a stronger than stock iron and a lighter alternative to most forged cranks. But, be forewarned, I have seen lightweight rotating assemblies with these cast steel cranks that rev so freely that they broke the crank snout off from the inertial resistance of the weight of the harmonic balancer and accessory drives. I have also seen blower cars break the snout of these cranks. In case you were wondering, this cast steel is what GM used to make their "Armasteel" parts out of (cast BOP rods) but I don’t know if the alloy is exactly the same. Let us now move on to forged. Starting with factory forgings. Factory forgings are usually found in some of the following engines; all 283's (3.00" and are all small journals), all Chevy 302's, small journal 327s (3.25"), some large journal 327's (3.25" have heard of and not seen), a few older 350's(3.48"), the LT4 350 (3.48" [1 piece late model rear main seal]), some 396-402 BBC (3.75"), never ever in any factory 400 SBC, some 427 BBB, and some 454 BBC. These cranks are forged using the same process as factory forged rods (except 7/16" bolt BBC) using a forged alloy called 1038 steel. I have seen many a small and big block Chevy using factory forged cranks where a race crank should have been up to 900 and 1000 hp. I do not recommend these power levels with a stock forging but it shows that you can get away with often. Factory forged cranks are also known for their lighter weight characteristics as far as forged cranks go. We next move to regular forged cranks and race cranks. Performance 4340 forged steel cranks, also known as Chromemoly, a lightweight extremely strong steel used to be as rare as buffalo nickels. Now they seem to abound everywhere. There are many manufacturers making and selling them in varying degrees of quality. From some manufacturers (like scat or cola) you can get everything from a base model big beefy model to a flyweight sprint car version ($$$$). Some are forged flat and then the journals are twisted into index while they are still hot while others are forged with these indexes (hence non-twist forging name) and amazingly some manufacturers will start with a high quality forged degassed block of 4340 and "whittle" it with a CNC machine, down into a little crank. These are the most expensive kind. All of this also all applies to the slightly stronger but heavier 5140 forged steel parts that are available lately. The one I am only slightly unsure of is this 4130 Chromemoly stuff. I understand it to be alloys of Chromemoly, the determining factor being, under a microscope the ratios of carbon and sulfur. But, I have seen 4130 items that are both forged like cranks and rods and cast which is usually rocker arms, usually referred to as investment cast. Many performance pushrods are made of this are 4130 Chromemoly. I believe the new LS1 motors have 4130 investment cast rockers as an example. I hope this has cleared things up, and if it has created more questions, then good. That is what research and discovery is all about.

LottaBallsCamaro

Didnt the LT1's in 1st and 2nd gen camaros have forged cranks?

B4Ctom1

Yes, those early (70's) lt1's are a great source for those cranks as well as, if you can get the whole motor and ARP the rod bolts and re assemble make a great little street motor with the 4 bolt mains and these are one of the (but not the only) motors that GM put forged pistons in.

ronterry

Didn't hear anything about GM favorite flavor ? 1010.

Or is it the same as 1038 ?


Here's how I remember which crank to use. Beer before liquor, never sicker --- Opps wrong one - never mind.

Ron

B4Ctom1

1010 and 1038 are so similar (as far as I know) that I used the more common 1038 designation. I was just thinking, I have seen different cranks made from the same materials as rods throughout history with one exception, powdered metal like the newest strongest mass produce rods the OEM is now using . . . Hhmmm!?!

destroyer1

I have heard both good and bad things about 4130 chromemoly. One person on ebay said that it was only good for sheet metal tubing like in bicycles and stuff because it had poor deep heat characteristics (like in a motor). Then someone from thirdgen told me that the guy on ebay was wrong and that he has used the 4130 cranks before even w/ nitrous. I trust the guy on thirdgen more but would like to hear more info on 4130 forged cranks. Any input would be greatly appreciated!

Kingtal0n

Just throwing this out there;

I have seen some aftermarket forgings, by SCAT and EAGLE, made from the strong 4340 forging... that came out of round. some of these were identified, there was a guy on ebay selling some of these eagle cranks already turned .010/.010 from eagle, and sometimes these are NOT caught, and are sent to customers with egg-shaped journals.

My advice to anyone purchasing a brand new aftermarket forgings is to triple check the journals. assembling a fresh motor with egg-shaped crank journals would be a def. no-no.

Red Devil

Good jobby job!! Maybe clean it up a bit and submit as an article.