I was recently asked if the difference between a cast crank and rods at $1200, vs FORGED at $1600 was worth the difference in cost by a guy who fully intends to race the car and has a high probability of using nitrous...
"

ITS ALMOST ALWAYS A BETTER IDEA to buy a matched balanced kit with all components supplied from a single source
heres a few IVE used with good results

http://chevyhighperformance.automotive. ... index.html


http://www.ohiocrank.com/rotatepage1.html

http://www.dougherbert.com/enginecompon ... 5f1f37f9e5

http://www.hotrod.com/howto/69883_strok ... index.html

http://www.popularhotrodding.com/tech/0 ... to_06.html

http://www.hotrod.com/howto/7234_cranks ... index.html
http://www.adperformance.com/index.php? ... ath=71_231

INTERNALLY BALANCED (SCAT, or LUNATI, or CROWER) 4340 steel FORGED KITS WITH 7/16" ARP rod bolts and clevite (H) bearings, and forged pistons are preferred in most cases, the scat 9000 cast steel cranks work ok for mild performance applications but INSIST on 7/16" ARP ROD BOLT RODS and ID strongly suggest INTERNAL BALANCING


you may find this info useful, on CRANK SHAFT STRENGTH
MATERIAL....................TENSILE STRENGTH.....PSI.
CAST
CAST IRON.....................APROX 75,000
NODULAR IRON................APROX 95,000
CAST STEEL...................APROX 105,000
FORGED
5140 forged steel.............APROX 115,000
4130.forged.....................aprox 123,000
4340 forged.....................aprox 143,000

think of it this way if you buy the cast/hyper deal you've WASTED $1200 PLUS, AND you'll need to spend an additional $1700,-1900 PLUS, the gaskets and machine shop costs if you ever want to upgrade, if you buy the forged set up you spent about $400 more than you wanted to but you'll never need to upgrade
you'll either spend the extra $450 up front or about $3000 total later????
you'll do fine with a cast steel crank and hyper pistons in a daily driver with about 400 hp,
but once your up into the 400HP-450hp plus range you should be thinking SERIOUSLY about FORGED COMPONENTS, buying a good quality forged and balanced rotating assembly is a bit like having several fire extinguishers in the shop, you hope the full intended strength or qualities are never used but its nice to know its there, even if its not needed frequently
in ANY supercharged or high rpm combo you'll be much better off with FORGED 2618 alloy pistons, hyper-eutectic pistons work great in low stress conditions but detonation ,heat, and high stress tend to damage them far faster than forged designs,detonation ,heat, and high stress and lack of cooling lube will kill any piston but forged designs tend to run for longer under the abuse before problems arise


So Grumpy, just to make sure I understand, you think I should buy the better kit? You're kinda riding the fence.

Just kidding, I get the feeling that if you could reach thru the computer you would be vigorously shaking me back and forth yelling "spend the freaking money"


"I get the feeling that if you could reach thru the computer you would be vigorously shaking me back and forth yelling "spend the freaking money"

that's .......what I get for using a cheap VOODOO DOLL,........... NEVER TRY TO USE LOW PRICE PARTS ON CRITICAL COMPONENTS
your NOT getting the message full strength if your only getting a (FEELING)......
by now you should be having SEVERAL REALLY NASTY 9 foot tall demons bouncing you off the wall and ceiling and having the
"spend the freaking money"
in flames on the wall, if the stupid VOODOO DOLL was working correctly




I posted this before
""5140 or 4340 ? Get the Facts and End the Confusion."

Before we can answer the question "which metal do I need in my crankshaft". I think we need to take a moment and review just what each metal is made of and what are the best applications for each. In the following discussion we will see the strengths and weaknesses of each and with this information we will be able to decide which Crankshaft material will best fit our needs.

Starting with the basics, metals containing primarily iron are classified as "ferrous metals". They range from pure iron through exotic high-alloy steels. Stock Crankshafts are made from cast iron, a metallic iron with more than 2 percent dissolved carbon. One preferred variation, ductile or nodular iron has all its carbon contained in the form of tiny spherical graphite nodules uniformly dispersed throughout the metal's matrix. This makes the material more ductile (deformable rather than brittle) and eases casting and machining.

Even the best cast iron has only limited tensile strength. Increasing ductility, hardness, malleability and fatigue resistance requires removing most carbon and at the high end, alloying iron with other elements, creating "steel" an iron with less than 2 percent carbon

The most basic form of this is carbon steel, which contains up to 1.7 percent carbon and minimal additional alloying elements. Carbon steels are designated by a four digit number. The first two digits indicate the basic type, and the last two digits indicate the approximate midpoint of the carbon content. The "10" ID's these alloys as non-resulfurized carbon steel with some manganese (popularly called medium-carbon or mild steel). The second two digits the "45" or "53" means the steel contains about 0.45 or 0.53 percent carbon respectively. Stock forged OEM cranks are usually made from 1045 or 1053 steel. There are exceptions to this, some 350 high performance steel cranks in the sixties were made from 5140 and some manufactures offer 5140 or 4340 in their high performance aftermarket catalogs.

From these mild OEM steels the next step up is Alloy steel. Alloy steels allow for more variations depending on the alloying materials. Over time as manufacturing techniques improved and chemical knowledge grew., metallurgist developed whole families of alloy steels, custom-tailored to make metals stronger, lighter, more durable, more ductile, and harder. Alloy steels are also identified by a four-digit number, with the first two digits indicating the major alloying element or elements, with the last two digits indicating the approximate midpoint of the carbon range.

We will now examine the four most common groups of steel, we will examine their best uses and hopefully come up with a buying criteria for making a decision on our crankshaft purchase. We want our purchase to be based on knowledge of the product and its intended use.



4130 The best known chrome-moly steel. It is a high-strength/high-stress alloy when produced in thin sections (sheet metal and tubing). But 4130 possesses very poor deep heat-treating characteristics which make it a bad choice for machined or forged parts.
--------------------------------------------------------------------------------


4140 A deep-hardening chrome-moly steel , it forges well and has good impact resistance, fatigue strength and general all around toughness.
--------------------------------------------------------------------------------


4340 A nickel-chrome-moly steel, this alloy is used to make premium cranks.4340 has good tensile strength, toughness, and fatigue resistance. Modified 4340 alloys with vanadium and more silicon can make this already good alloy even tougher and more fatigue-resistant. The main drawback is cost.
--------------------------------------------------------------------------------


5140 This chromium alloy increases tensile strength, hardness, toughness, and wear-resistance over carbon steel. It has the same basic elements of 4340 and is made with the same process but is more affordable.
--------------------------------------------------------------------------------


So what can we conclude from this short primer. Our first conclusion is that we don't want to purchase a crank made from 4130. The lack of deep heat treating properties makes it unacceptable for most performance applications. That leaves us with 5140 and 4340. Of the two we feel 5140 is the crankshaft material that suits most clients needs. Reason #1, based on feedback from clients using our cranks the 5140 crankshaft lasts as long as the 4340 when used in all but the most extreme racing conditions. For applications where the engine is putting out 800hp or less and turning 8,000rpm or less, 5140 is the right choice. Reason #2, in engine building you save money where ever you can, if it doesn't effect the performance or durability of the engine and our 5140 crankshafts are priced 30-40% below 4340 crankshafts in cost.

short answer,forged is best, cast steel is significantly stronger than plain cast iron and can be slightly more flexable, unfortunately, as the quality gets better the cost gets higher, and your connecting rods are FAR more likely to fail than the crank in most engine combos below about 6500rpm

http://machinistinfo.com/types_of_cast_iron.htm

http://www.key-to-steel.com/Articles/Art1.htm

http://www.seaportsteel.com/TechHeat.htm

http://crankshaftspecialist.net/cryogenics.html

http://www.campbellenterprises.com/cran ... cranks.htm

http://carcraft.com/techarticles/116_03 ... ndex1.html"

"Cast cranks weight less so the engine will rev quicker (like a light flywheel)"

thats a very comon MYTH!
keep in mind each crank casting or forging can be a totally differant design, and that the machine work done,and the weight of the total rotating assembly must be taken into account.
forged cranks can and frequently ARE lighter in weight , mosty of the weight is located in counter weights, a forged crank is generally used with FORGED rods and pistons and forged pistons and rods can be made both stronger and lighter at any given strength level, lighter rods/pistons allow for lighter counter weights.


example

http://www.scatcrankshafts.com/PDFs/ScatCrank07.pdf


if you compare carefully you'll see the BETTER forged cranks are LIGHTER than the BETTER cast cranks and the weights of both cast and forged cranks vary with the stroke and extent and quality of the machine work
the engine with the lighter rotating assembly only revs quicker in neutral, when its doing work (IE THE TRANS IS GETTING THE POWER TO THE REAR ) the car can only accelerate as fast as the CAR and tires,ETC will allow it to,
So true.

IF theres any way your going to invest in a decent aftermarket block as a base for a SBC you sure want a reliable/durable rotating assembly, ID strongly advise a 5140 0r a 4340 FORGED CRANK and 7/16" ARP rod bolt rods and a bit of thought as to the compression ratio, forged pistons and a decent valve train to avoid damage to the block
with a 4340 FORGED crank theres not much in the way of significant mechanical strength lost going to the more common 350 main bearing size journals and you reduce the bearing surface rotational speed just a bit so rotational frictions reduced slightly and most SBC cranks are designed for that bearing diam.
I got ask, (whats the differance between the one and two, piece rear seal cranks)



http://www.mortec.com/journal.htm

(look at the lower chart)

Gen.I, "Small Journal"
265...Mains-2.30"-Rods-2.00"
283...Mains-2.30"-Rods-2.00"
302...Mains-2.30"-Rods-2.00"
327...Mains-2.30"-Rods-2.00"

Gen.I, "Medium Journal", includes "Vortec" 305 and 350 thru '98
262...Mains-2.45"-Rods-2.10"
267...Mains-2.45"-Rods-2.10"
302...Mains-2.45"-Rods-2.10"
305...Mains-2.45"-Rods-2.10"
307...Mains-2.45"-Rods-2.10"
327...Mains-2.45"-Rods-2.10"
350...Mains-2.45"-Rods-2.10"

Gen.I, "Large Journal"
400...Mains-2.65"-rods-2.10"


CHEVY SMALLBLOCK V-8 Crankshaft Casting Numbers

SBC TWO PIECE REAR MAIN OIL SEALS

1130.......327.......forged..medium journal...3.25" stroke
1178.......302.......forged..medium journal...3.00" stroke
1181.......305,350...cast....medium journal...3.48" stroke
1182.......350.......forged..medium journal...3.48" stroke
2680.......327.......forged..small journal....3.25" stroke
2690.......350.......forged..medium journal...3.48" stroke
3279.......302.......forged..medium journal...3.00" stroke
3474.......283.......forged..small journal....3.00" stroke, military tank use
4577.......327.......forged..small journal....3.25" stroke
4672.......327.......forged..medium journal...3.25" stroke
310514.....350.......cast....medium journal...3.48" stroke
330550.....350.......cast....medium journal...3.48" stroke
354431.....262.......cast....medium journal...3.10" stroke
3727449....283.......forged..small journal....3.00" stroke
3729449....265.......forged..small journal....3.00" stroke
3734627....327.......forged..small journal....3.25" stroke
3735236....265,283...forged..small journal....3.00" stroke
3735263....283.......forged..small journal....3.00" stroke
3782680....327.......forged..small journal....3.25" stroke
3814671....327.......forged..small journal....3.25" stroke
3815822..265,283,302.forged..small journal....3.00" stroke
3835236....283.......forged..small journal....3.00" stroke
3836266....283.......forged..small journal....3.00" stroke
3848847....283.forged or cast..sm. journal....3.00" stroke
3849847....283.......forged..small journal....3.00" stroke
3876764....283.forged or cast..sm. journal....3.00" stroke
3876768....283.......forged..small journal....3.00" stroke
3884577....327.......forged..small journal....3.25" stroke
3892690....350.......forged..medium journal...3.48" stroke
3911001....307,327...cast....medium journal...3.25" stroke
3911011....307,327...cast....medium journal...3.25" stroke
3914672....327.......forged..medium journal...3.25" stroke
3923279....302.......forged..medium journal...3.00" stroke
3932442..267,305,350..cast...medium journal...3.48" stroke
3941174....307,327...cast....medium journal...3.25" stroke
3941178....302.......forged..medium journal...3.00" stroke
3941182....350.......forged..medium journal...3.48" stroke
3941188....350.......forged..medium journal...3.48" stroke
3949847....283..forged or cast..sm. journal...3.00" stroke
3951130....327.......forged..medium journal...3.25" stroke
3951529....400.......cast....large journal....3.75" stroke


SBC ONE PIECE REAR MAIN OIL SEAL

10168568...265.......cast....medium journal...3.00" stroke
12552215...364.......cast....medium journal...3.62" stroke, Gen. III, 6.0L
12552216...325,350,364.......cast....medium journal...3.62" stroke, Gen. III 5.7L LS1, 5.3L, 6.0L
12553312...293.......cast....medium journal, 3.27" stroke, Gen. III, 4.8L
12553482...293.......cast....medium journal, 3.27" stroke, Gen. III, 4.8L
14088526...305,350...cast....medium journal...3.48" stroke
14088532...350.......forged..medium journal...3.48" stroke
14088535...305,350...cast....medium journal...3.48" stroke
14088552...350.......forged..medium journal...3.48" stroke

and if your going to drop $1500 on a BARE BLOCK your probably going to want to try to insure it doesn,t get cracked when a cheap cast crank fails so an ALL FORGED AND BALLANCED ROTATING ASSEMBLY is a good idea.
CHEVY SMALLBLOCK V-8 BORE AND STROKE FROM
MORTEC.com


262 = 3.671" x 3.10" (Gen. I, 5.7" rod)
265 = 3.750" x 3.00" ('55-'57 Gen.I, 5.7" rod)
265 = 3.750" x 3.00" ('94-'96 Gen.II, 4.3 liter V-8 "L99", 5.94" rod)
267 = 3.500" x 3.48" (Gen.I, 5.7" rod)
283 = 3.875" x 3.00" (Gen.I, 5.7" rod)
293 = 3.779" x 3.27" ('99-later, Gen.III, "LR4" 4.8 Liter Vortec, 6.278" rod)
302 = 4.000" x 3.00" (Gen.I, 5.7" rod)
305 = 3.736" x 3.48" (Gen.I, 5.7" rod)
307 = 3.875" x 3.25" (Gen.I, 5.7" rod)
325 = 3.779" x 3.622" ('99-later, Gen.III, "LM7", "LS4 front wheel drive V-8" 5.3 Liter Vortec, 6.098" rod)
327 = 4.000" x 3.25" (Gen.I, 5.7" rod)
345 = 3.893" x 3.622" ('97-later, Gen.III, "LS1", 6.098" rod)
350 = 4.000" x 3.48" (Gen.I, 5.7" rod)
350 = 4.000" x 3.48" ('96-'01, Gen. I, Vortec, 5.7" rod)
350 = 3.900" x 3.66" ('89-'95, "LT5", in "ZR1" Corvette 32-valve DOHC, 5.74" rod)
364 = 4.000" x 3.622" ('99-later, Gen.III, "LS2", "LQ4" 6.0 Liter Vortec, 6.098" rod)
376 = 4.065" x 3.622" (2007-later, Gen. IV, "L92", Cadillac Escalade, GMC Yukon)
383 = 4.000" x 3.80" ('00, "HT 383", Gen.I truck crate motor, 5.7" rod)
400 = 4.125" x 3.75" (Gen.I, 5.565" rod)
427 = 4.125" x 4.00" (2006 Gen.IV, LS7 SBC, titanium rods)

Two common, non-factory smallblock combinations:

377 = 4.155" x 3.48" (5.7" or 6.00" rod)
400 block and a 350 crank with "spacer" main bearings
383 = 4.030" x 3.75" (5.565" or 5.7" or 6.0" rod)
350 block and a 400 crank, main bearing crank journals
cut to 350 size

Big Block Chevrolet Crankshaft Journal Sizes

BIG BLOCK CRANK JOURNAL SIZES
366T...Mains-2.7488"-2.7495" --- rods-2.20"
396...Mains-2.7488"-2.7495" --- rods-2.20"
402...Mains-2.7488"-2.7495" --- rods-2.20"
427...Mains-2.7488"-2.7495" --- rods-2.20"
427T...Mains-2.7488"-2.7495" --- rods-2.20"
454...Mains-2.7488"-2.7495" --- rods-2.20"
502...Mains-2.7488"-2.7495" --- rods-2.20"

All Chevy big blocks used

2.7488"-2.7495" - Mains
2.20" - Rods

BBC bore and stroke combos

366T = 3.935" x 3.76"
396 = 4.096" x 3.76"
402 = 4.125" x 3.76"
427 = 4.250" x 3.76"
427T = 4.250" x 3.76"
454 = 4.250" x 4.00"
496 = 4.250" x 4.37" (2001 Vortec 8100, 8.1 liter)
496 HOT ROD 454 stroker 4.310 bore x 4.25" stroke
502 = 4.466" x 4.00"
540 HOT ROD 502 stroker 4.50" bore x 4.25" stroke

572T = 4.560" x 4.375" (2003 "ZZ572" crate motors)

T = Tall Deck

ALL production big blocks used a 6.135" length rod.

before you read below Ill point out that Ive had excellent results with both hypereutectic and forged pistons when the engines are tuned correctly but Ive had some real disasters with detonation with hypereutectic pistons, as they seem far less tollerant of being abused, when the engines been adjusted badly by accident and you get into preignition or detonation, or an overly leam f/a mix, now forged will also fail but not as spectacularly.

http://kb-silvolite.com/article.php?action=read&A_id=38

PISTON ALLOYS AND HIGH PERFORMANCE

Which alloy is strongest? Answer, it doesn't matter. All piston alloys used by the industry today are strong enough, including cast iron. The real story is in more technical terms like fatigue strength, thermal conductivity, wear resistance, expansion rate, coefficient of friction and specific gravity.

Thermal conductivity is probably the least understood of all terms as it applies to a piston running in an engine. The effective conductivity of a piston (not the alloy) can be altered with coatings, surface area, section design, polish, and top land design. Ideally, the combustion surface of a piston would run at a little over 500°f and not exceed 600°f. The 600°f not-exceed temperature is the most important when it comes to engine life because a 600°f piston top can ignite the fuel mix independent of the spark plug.

Our performance is that we will make higher Hp and better low RPM torque with the best economy and smog numbers. It also suggests that we will have to maximize design efforts to cool the piston to keep the piston top below 600°f. On the opposite end of the spectrum regarding thermal conductivity is our forging alloy 2618. It is the most conductive alloy used by anyone making performance pistons. When the top gets hot the whole piston gets hot and expands accordingly. Noisy when cold and just fine when warmed up. The relatively cold piston top does hurt low RPM power and economy some, but design features can offset some of the shortcomings. Some forgings have been made with a slot at the oil drain back area for the purpose of restricting heat flow to the skirt. The design works and allows forgings to run almost as tight as hypereutectic pistons. Unfortunately, the heat slot weakens the piston below what is required for modern high Hp engines.

The coefficient of friction of all materials is pretty much the same when lubricated as the oil really determines how much slip you have. The unlubricated condition is the important number, especially since it is closely tied to wear and gauling. An engine seeing detonation tends to burn the oil off the cylinder walls. The surface finish on all KB Pistons is designed to put the oil back, but severe detonation can produce a situation with a dry cylinder and a tight piston. The hypereutectic alloys, those with at least 16% silicon (4% free particulate), have a structure somewhat similar to fiberglass. This hypereutectic alloy will slide on the free silicon when oil is not present. This phenomenon is what is responsible for the almost never-gaul never-wear reputation of KB Hypereutectic Pistons.

Specific gravity of piston alloys does affect the weight. Keith Black did make some magnesium pistons that worked. For the most part, though, most lightweight materials tried as piston material fall from thermal conductivity, wear, or fabrication problems. Currently the big savings in weight comes from design changes and the use of real long connecting rods.

Expansion rate varies from aluminum alloy to aluminum alloy with about a 15% total spread. Our forged pistons expand about 13% more than our hypereutectic. Big deal! 15% of 2/1000's of an inch is only .0003". Twice, nothing is still nothing. Why can't we run .002" clearance on performance forgings? The expansion of a piston is controlled by two factors, coefficient of thermal expansion and temperature. The expansion rate is the small player, but the temperature is drastically affected by the thermal conductivity of the piston. All successful forging alloys send combustion chamber heat to the piston skirt quickly, and hot skirts require the extra skirt clearance.

Strength and ductility are often confused terms. Most all pistons are more than strong enough at room temperature, with a slight edge going to the forging alloys. At high temperature the hypereutectic alloy has the edge strength-wise. The problem is if your pistons are 800°f and strong the engine is hypereutectic alloy is a slow conductor of heat. The benefit in in detonation mode and will continue to escalate temperature to destruction. (Direct injection engines may allow higher piston top tempertures.) Ductility is the main area where forging alloys really win. Short of breaking a wrist pin, forgings usually stay attached to the connecting rod even with nuts, bolts, and valve heads sharing the same combustion chamber space. A dropped valve on a forging is more likely to stick in the piston and limit damage to the cyliner head, rod, and piston.

In summary, we make forged 2618 and 18% hypereutectic pistons to hopefully offer the best piston choice to the end user. The hyper pistons have been designed to run forever and are a little more high tech. The forgings are safe. They are excellent when used in development type engines and some very high heat engines. Top fuel and 5 Hp/cubic inch plus engines see a lot of heat, and it is a little easier to cool a forged piston top. Hypereutectic pistons are a little less likely to form cracks than forgings because the alloy structure is somewhat like fiberglass. Cracks occur from flexing. The KB Hyper Pistons are designed not to flex. If the engine builder leaves a rod bolt in the intake, this soon becomes a component flex test. There are no winners ... and piston, cylinder, and cylinder head are usually proven not very flexible.

John Erb
Chief Engineer
KB Performance Pistons

don,t think you can,t use a cast crank!
cast is usually ok as long as the piston speeds are reasonable, the assembly is balanced and you've carefully checked clearances, but I generally prefer to keep the piston speed under 4000fpm for long term durability, as your pushing things at that point in many cases

http://www.csgnetwork.com/pistonspeedcalc.html

http://www.circletrack.com/techarticles ... index.html

http://en.wikipedia.org/wiki/Ductile_iron

http://www.circletrack.com/drivetrainte ... index.html

youll generally find its the valve train,and valve train control issues and its not the rotating assembly that causes problems well before that piston speed becomes a factor

FROM THE SCAT CRANK SITE
http://www.scatcrankshafts.com/

So . . . What the heck is NITRIDING?

The nitriding process, unlike induction hardening, is done in
an oven. The cranks are suspended in a closed chamber
which is lowered into the furnace for heating. At a
determined temperature, amonia and nitrogen gas is
introduced into the chamber and circulated all around the
cranks and chamber. This heated gas reacts with the
carbon on the surface of the crank at a depth of
approximately .010, making the surface hard.
Nitriding is done at a temperature that is less than
the critical temperature which, unlike induction
hardening retains maximum strength of the core of
the crank.
Nitriding treats the crank evenly from top to bottom
and side to side. It sets up a surface tension that
stiffens the crank and increases the fatigue life by 18%
to 20%. Induction hardening sets up stress risers that
lowers the fatigue life.
The process is expensive. The equipment is very high tech
and is computer controlled. It has high energy and labor
cost. Typical cycle time is 24 or more hours in the furnace.
It uses expensive ammonia and nitrogen gas. The process is
designed for each specific alloy steel. If the steel is not to
spec, the crank will come out of the oven bent, broken or
swollen. In reality, the nitride process is SCAT's 100%
check of the steel to make sure that each crank a customer
receives is exactly what we say it is.
Are there any down sides to nitriding? And the
answer is yes, there are two.
1) If you have a failure and the crank requires regrinding to
restore surface hardness, you must re-nitride the crank.
But then the crank is new again. Some say you should
have more confidence in yourself than planning to rebuild
before you have even run the engine for the first
time.
2) Cost . . . You know the saying . . . You get what you pay
for. There is no question a nitrided process is more
costly. SCAT is committed to excellence and therefore
will not compensate the quality of our crankshafts by
using an inferior heat treating process to save money.
By using Hi-tech equipment and processing we are able
to furnish our customers the finest performance cranks
at an affordable cost.
Ion

PISTON ALLOYS AND HIGH PERFORMANCE

Which alloy is strongest? Answer, it doesn't matter. All piston alloys used by the industry today are strong enough, including cast iron. The real story is in more technical terms like fatigue strength, thermal conductivity, wear resistance, expansion rate, coefficient of friction and specific gravity.

Thermal conductivity is probably the least understood of all terms as it applies to a piston running in an engine. The effective conductivity of a piston (not the alloy) can be altered with coatings, surface area, section design, polish, and top land design. Ideally, the combustion surface of a piston would run at a little over 500°f and not exceed 600°f. The 600°f not-exceed temperature is the most important when it comes to engine life because a 600°f piston top can ignite the fuel mix independent of the spark plug.

Our performance is that we will make higher Hp and better low RPM torque with the best economy and smog numbers. It also suggests that we will have to maximize design efforts to cool the piston to keep the piston top below 600°f. On the opposite end of the spectrum regarding thermal conductivity is our forging alloy 2618. It is the most conductive alloy used by anyone making performance pistons. When the top gets hot the whole piston gets hot and expands accordingly. Noisy when cold and just fine when warmed up. The relatively cold piston top does hurt low RPM power and economy some, but design features can offset some of the shortcomings. Some forgings have been made with a slot at the oil drain back area for the purpose of restricting heat flow to the skirt. The design works and allows forgings to run almost as tight as hypereutectic pistons. Unfortunately, the heat slot weakens the piston below what is required for modern high Hp engines.

The coefficient of friction of all materials is pretty much the same when lubricated as the oil really determines how much slip you have. The unlubricated condition is the important number, especially since it is closely tied to wear and gauling. An engine seeing detonation tends to burn the oil off the cylinder walls. The surface finish on all KB Pistons is designed to put the oil back, but severe detonation can produce a situation with a dry cylinder and a tight piston. The hypereutectic alloys, those with at least 16% silicon (4% free particulate), have a structure somewhat similar to fiberglass. This hypereutectic alloy will slide on the free silicon when oil is not present. This phenomenon is what is responsible for the almost never-gaul never-wear reputation of KB Hypereutectic Pistons.

Specific gravity of piston alloys does affect the weight. Keith Black did make some magnesium pistons that worked. For the most part, though, most lightweight materials tried as piston material fall from thermal conductivity, wear, or fabrication problems. Currently the big savings in weight comes from design changes and the use of real long connecting rods.

Expansion rate varies from aluminum alloy to aluminum alloy with about a 15% total spread. Our forged pistons expand about 13% more than our hypereutectic. Big deal! 15% of 2/1000's of an inch is only .0003". Twice, nothing is still nothing. Why can't we run .002" clearance on performance forgings? The expansion of a piston is controlled by two factors, coefficient of thermal expansion and temperature. The expansion rate is the small player, but the temperature is drastically affected by the thermal conductivity of the piston. All successful forging alloys send combustion chamber heat to the piston skirt quickly, and hot skirts require the extra skirt clearance.

Strength and ductility are often confused terms. Most all pistons are more than strong enough at room temperature, with a slight edge going to the forging alloys. At high temperature the hypereutectic alloy has the edge strength-wise. The problem is if your pistons are 800°f and strong the engine is hypereutectic alloy is a slow conductor of heat. The benefit in in detonation mode and will continue to escalate temperature to destruction. (Direct injection engines may allow higher piston top tempertures.) Ductility is the main area where forging alloys really win. Short of breaking a wrist pin, forgings usually stay attached to the connecting rod even with nuts, bolts, and valve heads sharing the same combustion chamber space. A dropped valve on a forging is more likely to stick in the piston and limit damage to the cyliner head, rod, and piston.

In summary, we make forged 2618 and 18% hypereutectic pistons to hopefully offer the best piston choice to the end user. The hyper pistons have been designed to run forever and are a little more high tech. The forgings are safe. They are excellent when used in development type engines and some very high heat engines. Top fuel and 5 Hp/cubic inch plus engines see a lot of heat, and it is a little easier to cool a forged piston top. Hypereutectic pistons are a little less likely to form cracks than forgings because the alloy structure is somewhat like fiberglass. Cracks occur from flexing. The KB Hyper Pistons are designed not to flex. If the engine builder leaves a rod bolt in the intake, this soon becomes a component flex test. There are no winners ... and piston, cylinder, and cylinder head are usually proven not very flexible.

John Erb
Chief Engineer
KB Performance Pistons

keep in mind a high percentage of " crank failures" were the RESULT of lubrication systems that were not set up properly, connecting rod bolts that stretched or main caps that flexed, not really crank failures, at all!

http://www.popularhotrodding.com/tech/0 ... to_06.html

http://www.carcraft.com/techarticles/11 ... ndex1.html

http://www.campbellenterprises.com/cran ... cranks.htm

http://www.popularhotrodding.com/tech/0 ... index.html

http://www.steel.org/AM/Template.cfm?Se ... NTID=33458

http://www.chevyhiperformance.com/tech/ ... index.html

http://www.badasscars.com/index.cfm/pag ... /prd85.htm

Are forged cranks stronger than cast cranks?


Yes they are. In the days gone by, forged steel cranks were the way to go and they still are if you're building an all out racing engine. Some factory engines came with forged cranks. The stock small journal 327's and 283 ALL had forged steel cranks. Some of the early high performance 350's came with forged cranks as well. There are many types of steel used for making cranks though, be them cast or forged and some cast cranks these days are just as strong (if not stronger) than older forged ones. There used to be just cast iron, nodular iron and forged steel available. Now, for the most part, there's cast steel, 4130 and 5140 forged steel and super strong 4340 forged steel available. The new cast steel cranks are very cost effective and plenty strong for even most mild racing engines. I have seen forged cranks break in half for no visible reason at all, yet I have seen cast cranks survive season after season in mild race cars. I recommend using forged cranks in serious street and race engines, and stroker's, especially if you are using nitrous or a supercharger. Stay away from the Chinese and Taiwan made junk. I am not a fan of the Mexican made forged cranks either. Those come is all of the late model factory crate engines. Comparing those types of cranks to a high quality crank is like comparing a Chinese made 6 dollar set of sockets to a high quality / high strength set of 80 dollar Snap-On or Mac Tools sockets. There's no comparison, especially when you find-out the cheap, Chinese sockets break the first time you try to use them. Well, "steel" cranks aren't any different except for the fact that when you go "cheap" in an engine, you are asking for a MAJOR failure that takes everything else along with it. Is that worth it? No way! That's why we don't use that kind of crap in our engines, but you sure see that crap in all of the "bargain priced" magazine ad engines out there. You certainly don't need a $4,000 profiled, ultra light, billet steel crank like you'd find in a Nascar engine, or even a $1,500 high quality forged steel crank in well built street / strip engine, but you also certainly don't want to run a $189.00 piece of crap crank in an engine that is going to make some serious power. Just remember, you get what you pay for.


http://www.nastyz28.com/sbcmenu.php

http://www.ohiocrank.com/chevysb_cranks.html

http://www.ohiocrank.com/hbeam_rods.html




cast on left forged on the right


cast on left forged on the right

http://www.youtube.com/watch?v=xIBG0hfR ... re=related

For the visually challenged, a forged crank can be identified by ear. A forging will ring like a bell when tapped on the counterweight with a steel hammer, while a casting will give a dull thud.
http://www.youtube.com/watch?v=xIBG0hfR ... re=related

watch this video to hear the difference