Scat or Eagle.

What are the main differences besides material selection. Both forged. HP rating "800+" on 4130 and 1000+ on 4340, I know those are manufacturers ratings and dont mean much, but why are 4340s so much better?

Also Ive asked a few people, but want more opinions on ground mains, only .010" under, by the factory, assuming it is done right, any disadvantages.

 

I think I already gave you my viewpoint on the journals, but done right 10 under is no problem at all. As far as 4130 v. 4340, the 4340 is a stronger alloy.

tensile strength
4130 ~200,000psi
4340 ~220.000psi

For street and street strip use a 4130 crank is likely plenty strong, assuming it is properly designed and manufactured. The thing is, there isn't much difference in the price of the materials. Most of the cost is in the machining. So if a 4130 piece is considerably cheaper, it may well be that is not of the same quality. Most good cranks will be made of the stronger material. Callies, for instance, uses 4340 in all their cranks.

And not all steels of the same alloy are of the same quality. Price, and quality, can vary tremendously. So the same caveat applies.

Rich Krause

 

4130 is an alloy of chromium and molybdenum (hence "Chrome-Moly") and 3/10 of a percent (.3%) carbon. The carbon allows it to be directly hardened to the strength Rich pointed out. This is not enough carbon to directly harden to a high hardness like Rc60 on a journal, so if this is necessary, a carbon/nitrogen layer or "case" needs to be added. Nitirding is an example.

Both Cr and Mo increase tensile strength toughness and hardenability as well as resisting wear and corrosion. Mo helps at elevated temps, but that's not a concern with a crank or rods.

4340 has nickel added to the chromium and moly of 4130. The nickel also increases strength and hardness without hurting toughness and ductility, or the ability to to be formed or forged without breaking. The .4% carbon (the "40" in 4340) may allow a little more direct hardness, but .3% C would get the steel to the hardness range used in cranks.

4340 is used extensively in aircraft parts, and is often availabe in AQ or Aircraft Quality form. This often means the metal was double vacuum melted, or melted twice in a vacuum furnace to help eliminate any impurities which might cause weaknesses. Chemistry and physical propeties of the raw billet are better controlled, and each heat has a long "pedigree" which comes with it. This drives up the cost, but helps assure a not only stronger, but more consistent product.

For lots more on metallurgy of race engine and racecar parts, see Engineer To Win by Caroll Smith. I plagerized some of it for this response because I like the way Caroll wrote.

 

I should have waited for Jon to answer, he knows a LOT about materials.

Rich Krause

 

But he don't know squat about taking people apart and puttin' them back together so they work.

 

Well guys, thanks for the info, not that I can understand most of it , but it did help, now I just have to make a decision whether the extra $150 is worth it, I tend to think so, just didnt want to spend it if it wasnt necessary, it really probably isnt, but like I said before...ohwell!

Jon

 

So what are your power and durability expectations for the engine? If the "cheaper" crank is plenty strong, spend the extra bucks on gettin' air in and out.

There's a lot of discussion going on about bottom end strength. The best crank in the world won't survive a weak block when the power gets high enough. Match up the parts.

 

As the old man said how much do you need?

A street car can get away with a Scat 9000 but if you need more than that no point in going to a 4130 Forged in my opinion. A forged crank is a good choice if you are going to hang a hairdryer off the front end of it.

Hey pops why don't you add in 1053, 5140 and EN40B as forged material choices also.

Another note, block materials. The old school small blocks had a 10, 20 or a 10/20 on the front of the block which talked about the same additional materials as are added to the meld in crankshafts.

a 10/20 block which is preffered is a 1% Tin 2% Nickel block. The Nickel content of the block does two things it refines the grain structure (astenitie/martensite etc) which increases the strength and work hardening characteristic. This gives a longer service life of the block.

The Tin in the block helps the pouring of the cast iron and makes the cast iron more ductle so it is less prone to cracking. Also since they pour more easily they also have a more consistent densitiy to them.

If the block just has a 10 or a 20 that's the percentage of nickel in the block.

The Bow Tie block is a high nickel content block, I'm not sure how much nickel but it is at least 2%.

Bret

 

Well, it will be totally NA for most of this year, maybe by the end of the season a 200 DP shot.

Bottom will consist of 6" Eagle Hbeams
SRP Nitrous/Blower pistons -16cc 1.125"CH
JE plasma moly rings
Nutek 4bolt main caps
Front billet 2bolt cap, unsure brand
ARP main studs
ATI balancer, might stay stock for a few weeks, not sure yet

Heads are stock by Lloyd with 2.0/1.56 ferrea 6000 valves
Cam will be by Joe Overton (977 springs/hardware)
Intake is stock welded and ported by me
30# injectors for now, hopefully theyll be enough
LTs, 3" catback with 2 cutouts at collectors


Im shooting for 450 at the wheels, should be doable, it will all depend on how good of a job Joe does on the cam, which im sure will be awesome, I believe thats where all the power missing in these stroker LT1s is, the cam, and joe seems to be the best.

I want it to last AT LEAST 2 years no problem, can tear down and do rings/bearings each winter though. It will have Amsoil running through it.

The most nitrous it would EVER see is 300, but more likely 250.

One other thing, if you are recommending what crank, base prices on these.

Eagle 4340 3.75 Mains ground .010 by eagle .... $375
Eagle Lightweight groung .010 by eagle............. $385
Scat 4130 3.75 .................................................. .$359
Eagle 4130 3.75.............................................. .....$379
Eagle 4340.............................................. .............$539
Scat 4340.............................................. ...............$539

Edit, forgot to mention the block will have full machinwork by a guy that builds 7s cars around here, never had work done there, but many friends trust him.

Line bore
bore/hone w/deckplate
deck to .005
all the rest of the stuff and balancing/assembly (not sure internal or external...opinions?)

 

So whatdya think...I want to get the crank and rods ordered within the next two weeks, and dont know what to get

 

Ask your engine/cam designer for his recommendation. He knows more about your engine and your expectations than anyone here, or at least he should if he's specing the cam!


Whatever you choose, buy it new. If it were my engine, and a Scat 9000 wasn't enough, I'd go all the way to 4340 and skip anything in between.

My $.02

 

Sounds like excellent advice to me.

Rich Krause

 

Problem is, Im young, and dont have any experience with engine builders in the area, Im going off word of mouth for the guy thats doing the machinework and assembly and everything that he is a good builder and wont screw it up, but I think I trust all you guys' opinions more for now. I guess I could call Joe Overton and ask his advice since he will be grinding the cam for me, Im sure he would know. Ill probly do that tomorrow, but feel free to chime in with your advice, I appreciate it.

Jon

 

Well, I think im gonna just go with my instinct on this one, and hit up the 4130 crank. I never thought about a 9000 crank, but I think after listening to you guys, that it would "probably" suffice to what Ill end up throwing at it, but I dont want to take that chance, and Im saving $200 going with it over a 4340, and I think it is plenty strong....I can spend that extra $$ on machining where its probably most important. Good idea?

 

What is wrong with these two?

Eagle 4340 3.75 Mains ground .010 by eagle .... $375
Eagle Lightweight groung .010 by eagle............. $385

Are they just factory blems?

Jon, seriously the old mans advice was pretty cut and dry. BUY A 4340!


Bret