I'm currently building a 496bbc. I'm just curious if a forged crank is worth the extra money. I'm going with forged pistons and h-beam rods. I was told that a forged crank is not necessary for my power goals (600-675.) I'm just thinking the extra money may be worth the piece of mind. This will be for a street car.

Thanks in advice

Always build it better. If it breaks, fix it faster. I always go over the top because if you do it right the first time, you will not have to address it again for a long time. A forged steel crank is definitely the way to go.

ak,
I am going to go the other direction. For a street driven car, with the power level you are talking about, a cast steel crank should be more than enough. As far as that goes, the H beam rods are probably not needed either. There are plenty of old school 600 HP big blocks using GM dimple rods, cant say I have ever seen one break without something else being the cause. One of my customers just dynoe'd a Marine 502 at 625 hp, GM dimple rods there. Use the money you save on something else.

Just my opinion,

ak,
I am going to go the other direction. For a street driven car, with the power level you are talking about, a cast steel crank should be more than enough. As far as that goes, the H beam rods are probably not needed either. There are plenty of old school 600 HP big blocks using GM dimple rods, cant say I have ever seen one break without something else being the cause. One of my customers just dynoe'd a Marine 502 at 625 hp, GM dimple rods there. Use the money you save on something else.

Just my opinion,
Ditto. Cast is plenty for just street use. IMO.

capt

Opinion: take it for what it's worth, but tell that to the guy who just bought my old motor because he was told the same on stock crank and gm rods... as they came out of the motor. Not even making 400-425hp. (110mph 65 nova). Not to say you can't get away with it and be fine, but myself, over the 450hp mark, forged crank and aftermarket rods.

Edit-- correction, thought he was talking 600hp small block on cast bottom end! I'd still upgrade the rods though. my bad.

The Eagle rotating assembly I got is good to 700 hp with cast crank and I-beam rods.
Moving up to forged crank and H-Beam rods was another $1000.00.
Or I could have gone for 1500hp and spend another $1600.00 and gotten the super-duper ARP bolt upgrades.



I went the cheaper route and spent the money on my heads. If you plan on producing more than 700hp (on a big block) then I'd consider it otherwise it is overkill imho. But then again we car guys like to keep upping our HP, but that goes back to what you want the car to do.

I am going with the cast crank myself. I ran a 13 to 1, 468 in my drag car for about two years. The cast crank and dimple rod did me good. It saw 7500 on more then one time......But maybe I got lucky.I would use the same stuff if I did it agine....:thumbsup:

Stock big block bottom ends are strong. I'd trust one at 600hp.

Exactly,..500 HP is child's play for a BB cast crank but would be at the danger threshold in a SB.

Here's a compromise,..the Scat 9000 cranks. Stronger than typical cast cranks and priced right,..about $300. More here:

http://www.scatcrankshafts.com/

I'm currently building a 496bbc. I'm just curious if a forged crank is worth the extra money. I'm going with forged pistons and h-beam rods. I was told that a forged crank is not necessary for my power goals (600-675.) I'm just thinking the extra money may be worth the piece of mind. This will be for a street car.

Thanks in advice

A cast crank is fine for your application.Will easily support your power levels.The weak link is in the rod bolts.Invest in qaulity fasteners.Stock thumb rods are strong..but you will most likely want to go to a 6.385" rod length with the 4.250" arm.

I've spend money twice too many times with my car - with it all apart I would upgrade, although forged might not be necessary to me its cheap insurance. My new motto is, do it once and do it right :D

Cry once.....not TWICE!!

I was going through the same issue when I rebuilt my 350. I figured I go forged so I wouldn't need to tear into my bottom end if added more power in the future. Then I realized, that I would just be wasting money since the stock bottom end would hold up fne. No point going forged if the stock bottom end will more than meet your needs. If it gives you piece of mind, go for it but remember you could have spent that $$$ elsewhere and seen more results.

GM used steel cranks in all of their performance motors, cast in only the grocery getters. Proof enough for me.

GM used steel cranks in all of their performance motors, cast in only the grocery getters. Proof enough for me.
:yes::hurray::beers::thumbsup:Trucks too. It's not just strength, it's cycles. Number of times the crank rotates before failure/crack.

Go with the Scat piece it's a very good low cost investment that will handle 700+ hp.

Jim: I'm surprised. No mention of Bertha :confused: :D


http://i20.photobucket.com/albums/b217/RamAirDave/100_0888.jpg


It's gonna make a nice wind chime at our new shop :yes:

Damn-it!

You ain't supposed ta drop a cast crank on the floor!!

He, He!!

pdq67

Jim: I'm surprised. No mention of Bertha :confused: :D


http://i20.photobucket.com/albums/b217/RamAirDave/100_0888.jpg


It's gonna make a nice wind chime at our new shop :yes:


===========================
From the pic at distance those are textbook torsional failures. I'd love to see that thing under a bright light.
Are there any 'ratchet' or 'beech' marks in the failures?

Neat thing about an engine shaft failure like this one is it leaves clues because parts of the shaft don't strike one another. Most shaft failures I diagnose pulverize all clues though.

A torsional failure always has that angular fracture.

That's not a tortional fracture.....that's a broken crank!!!

Was that a 4" stroke or a little more (say 4.25")???

You guys are making me feel better about just how much HP a cast crank will hold. Are there any guesses out there of how much, if any, that an aftermarket cast crank (scat) is in strength compared to a factory GM cast crank???

As yourself these questions:

1) Did the legendary 427 L88 have a forged steel crank?
2) Did the ultra legendary 427 ZL1 have a forged steel crank?
3) Did the legendary 454 LS6 have a forged steel crank?
Ok Ok you say those engines were not factory installed into first gen's.

Well how about a 4th question

4) Did the 396 L78 have a forged steel crank?

The answer to all 4 questions is a resounding YES!

My 2 cents: It's better to have something overbuilt and under stressed than something that is over burdened and possibly not up to the task. Go with the forged steel crank. These four engines including the 396 L78 also had 4 bolt mains. They were brutes, kicked all forms of (censored), and did not have time to take names. That's just the way I like things!

Have a great day!!

Greg aka SSG&H

And those engins killed the Street Hemi. But don't tell that to Barret Jackson bidders. They still think that a production run of 12 means the combo is special, not (cencored too)

From Powerhouse for a 454 crank!

http://shop.enginekits.com/osb/itemdetails.cfm?ID=969

And for a 496 crank!

http://shop.enginekits.com/osb/itemdetails.cfm?ID=970

And I'm sure that you can find 427 cranks too w/ prices to match. Just have a GOOD Machinist check it out...........

Also look at Competition Products..

One other thing is please consider talking to Mike, Gary or Carl about a Pro rotating assembly too................

pdq67

Thanks for the info guys. I appreciate all the input. The crank I have is an eagle but it is cast. I'm curious if the eagle will accept for punishment. I'm leaning toward spending the extra cash for a forged piece.

I'd love to see that thing under a bright light. Are there any 'ratchet' or 'beech' marks in the failures?

Tim, I have no idea what ratchet or beech marks are :confused: I can get some close pics if you're really interested.

Structural failure analysis terms?

alan

Tim, I have no idea what ratchet or beech marks are :confused: I can get some close pics if you're really interested.

Thanks Dave, but digital pics rarely capture the detail. The best pics I have of the best failure(for inspection purposes) I've ever seen tell a completely different story than a visual in broad daylight does. That's why I said I'd love to see it under a bright light. Ratchet marks would look like a stair step in the break somewhere. Beech marks look vaguely like this ((((((((

It's just clues to the type of failure.

Yes Alan, failure analysis terms.

I ran a stock GM Cast Crank for years in a 454; however, I did cross drill it. The engine had typical Holley 750 DP/ Edelbrock RPM, Crane Fire Ball, Headers to M21 and various rear gears. I would estimate 425 Hp and it saw many 6000 rpm shifts. I eventually went Forged only because I went Mechanical Roller and the engine can shift at 7000 rpm. After years of abuse that cast crank was in perfect shape when I took it out and it made me wonder if a forging was worth the money, but then again with 600 Hp a Forged Crank is assuring.

One thing to consider is that a Forged Crank is considerably Heavier then a Cast one.

And please consider Ohio Crankshaft Company as well as Competition Products and good old Speed-O-Motive for cheap BB rotating assemblies!

And please if you get one, have a GOOD Machine Shop check the whole deal out like Mike and Carl say.

pdq67