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Technical cast steel crank vs. 4340 moly, Eagle

Discussion in 'The Hokey Ass Message Board' started by Budget36, Oct 17, 2019.

  1. Budget36
    Joined: Nov 29, 2014
    Posts: 2,308

    Budget36
    Member

    I want to make a small block chevy a 383 for a tow rig, any reason the cast steel Eagle crank won't hold up, or should I step up to the 4340 Moly crank? 320 vs 620 dollars wise. Not looking to cheap out, but don't need a Marine engine, i/e doesn't need to be the best it can be.

    Might see 2-3K miles a year, max RPM's when the TH400 shifts pulling up a hill...maybe 5K-5.5K

    Anyone have insight?
     
  2. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,189

    dirty old man
    ALLIANCE MEMBER

    This is a point of disagreement amongst lots of engine building people. But myself I feel that if you're building a race oriented engine that you're,shifting @ 7K, ect,. yeah, you most likely will get better service outta the 4340 forged crank.
    But for the duty you describe, I think the cast crank should do just fine.
     
  3. Oldioron
    Joined: Dec 12, 2018
    Posts: 908

    Oldioron
    Member

    Think 300 would cover the tow bill?
     
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  4. Mike VV
    Joined: Sep 28, 2010
    Posts: 1,574

    Mike VV
    Member
    from SoCal

    NO one makes OR sells a "Moly" crank shaft..!
    Do you mean "Chromoly" ? Just calling it 4340 is a plenty good description.

    Again...details matter.

    Mike
     
    19Eddy30 likes this.
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  5. chevy57dude
    Joined: Dec 10, 2007
    Posts: 4,995

    chevy57dude
    Member

    Ask the opinion of your reputable, trusted engine machinist. He can tell you how many broken cranks have come back. Probably not many.
    450 lb/ft is possible, right? Spend the extra money on roller rocker arms and enjoy the horsepower.
     
    31hotrodguy likes this.
  6. partsdawg
    Joined: Feb 12, 2006
    Posts: 2,422

    partsdawg
    ALLIANCE MEMBER
    from Minnesota

    How many 1990 and older trucks out there with the factory 350 have you heard of breaking cranks?
     
  7. badvolvo
    Joined: Jul 25, 2011
    Posts: 367

    badvolvo
    Member

    I have run the scat cast steel crankshafts in a lot of small blocks, up to 600 hp without issues. Honestly, I built a 406 over 20 years ago with the stock cast crankshaft, the car run's in the 10's and has not been apart since it was built.
     
  8. treb11
    Joined: Jan 21, 2006
    Posts: 3,232

    treb11
    ALLIANCE MEMBER

    For $620 you will NOT be getting a race grade forged crank. The standard crank will be fine. Use the $ on a balanced rotating assembly.

    Sent from my SM-G965U using The H.A.M.B. mobile app
     
  9. Budget36
    Joined: Nov 29, 2014
    Posts: 2,308

    Budget36
    Member


    Here's the Description:

    Crankshaft, 1-Piece Seal, Internal Balance, Forged 4340 Steel, 3.750 in. Stroke, Chevy, 5.7L, Each


    https://www.summitracing.com/parts/esp-435337505700?rrec=true
     
  10. southcross2631
    Joined: Jan 20, 2013
    Posts: 2,920

    southcross2631
    Member

    I think it's overkill for a tow rig. I ran a big block Chevy with a stock cast crank and turned it 7 grand for 3 years before it jerked a rod journal out after I started spraying 200hp of nitrous every pass.
    I had a documented 500 passes on that crankshaft. It was a used crank that I had turned and checked for cracks.
    A cast steel Eagle or Scat would do fine in your truck. My friend ran a cast steel 383 kit in his motor home for years pulling a 24 foot enclosed. Eagle crank, Eagle I beam rod's, Hyper piston's. The kit back then was less than a thousand dollars with a flexplate and balancer.
     
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  11. anthony myrick
    Joined: Sep 4, 2009
    Posts: 4,441

    anthony myrick
    Member
    from al

    We almost built a stroker for our tow rig
    went with a 500 caddy
    the cast crank should be fine, as long as ya don't put a blower on it
    seen some front hubs break
     
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  12. Budget36
    Joined: Nov 29, 2014
    Posts: 2,308

    Budget36
    Member

    Thanks all. Again, building for low end torque, won't be blown, revved high, etc.
     
    chevy57dude likes this.
  13. *Every* chevy stock 400 crank was cast. How many of those with cut down (from 400 sized to smaller 350 size diameter) mains to be made into 383's before the aftermarket cranks became popular and more available at lower cost? Ever hear of those original 400 cranks breaking, even in racing applications? Not really an issue, you will be fine with the cast crank in your tow engine. Agree, spend the saved money on a good balancing, that will provide better benefit than the forged vs cast.
     
    scotty t, Deuces, 31hotrodguy and 2 others like this.
  14. jimmy six
    Joined: Mar 21, 2006
    Posts: 4,642

    jimmy six
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    For a tow rig.. why stop with a 3.750"... I'd go with a 3.875" or 4" . make a real torquer.
     
  15. Truckdoctor Andy
    Joined: Jan 13, 2017
    Posts: 847

    Truckdoctor Andy
    Member

    I had a cast crank in my O/T Nova Drag Car. I was young and broke. Spent all my money on the top end. Sportsman 2 heads, Crane Cam, Vic Jr., etc. the bottom end was stock Chevy Truck. Four bolt block, cast crank, stock rods, stock rod bolts. It even had some of those 12to 1 cast “claimer” pistons in it. 4.86 gears in the 9 inch and 7300-7400 through the traps every run for three years until I sold it. For some reason, sometimes stuff that isn’t supposed to work does. By the way, I don’t recommend this. Your results may vary.


    Sent from my iPhone using The H.A.M.B. mobile app
     
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  16. Budget36
    Joined: Nov 29, 2014
    Posts: 2,308

    Budget36
    Member


    Gotta read some:) The truck won't see but 4-5K miles a year. I mean I could go BBC, hell, find a 496 out of pick and pull...heck...I could fit a duramax in it...hell, I could find an old Pete or KW (eff the cab over Whites) and run a big cam 400...I could...

    Well, tis why I'm not. Not going to make a living with it;)
     
  17. jimmy six
    Joined: Mar 21, 2006
    Posts: 4,642

    jimmy six
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    Budget, our sporadically used tow rig has a 496 oddball and is a torque monster; 12 mpg empty and 11.5 when towing. On the trailer is a 1/2mile Super Stock dirt Camaro with the 422” all iron Dart.:):):)
     
  18. deathrowdave
    Joined: May 27, 2014
    Posts: 1,775

    deathrowdave
    ALLIANCE MEMBER
    from NKy

    Never heard of a cast steel crank , I was thinking it was a cast ductile iron . I didn’t know it was cast steel . As far as forged , I was very sick ( stage 4 cancer ) , I sent my LT1 forged steel crank to the machine shop , they snapped into 2 pieces . WTH , I went to pick it up , ended up tossing it into the dumpster , installing a cast crank and done . I just had way to much going on to press the shop owed me a crank.
     
  19. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,189

    dirty old man
    ALLIANCE MEMBER

    I think I would give serious consideration to a big block like a truck 454. Very little stress on engine parts and lots
    of torque.
    But since this is a low budget project, a lot depends on what you already have on hand.
     
    kidcampbell71 likes this.
  20. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,273

    sunbeam
    Member

    When you turn down the mains .200 from a 400 you lose a lot of journal over lap I would spring for the better crank. There is a reason Chevrolet increased main size between a 327 to 350 and a 350 to 400.
     
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  21. jaw22w
    Joined: Mar 2, 2013
    Posts: 835

    jaw22w
    Member
    from Indiana

    .
    What exactly is journal overlap? Never heard of it.
     
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  22. porknbeaner
    Joined: Sep 12, 2003
    Posts: 41,051

    porknbeaner
    Member

    A cast crank if its a good one will hold up just fine in a tow rig.
     
    dana barlow, ottoman and Deuces like this.
  23. anthony myrick
    Joined: Sep 4, 2009
    Posts: 4,441

    anthony myrick
    Member
    from al

    The 350 in my ride came from a gm 1ton. 11k gvw
    Cast crank from the factory.
     
    Deuces likes this.
  24. dreracecar
    Joined: Aug 27, 2009
    Posts: 2,806

    dreracecar
    Member
    from so-cal

     
  25. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,273

    sunbeam
    Member

  26. 315,000 miles on a tow happy, 8 passenger, stock, GM crank, 350, 29 year old vehicle.

    Also ... beat to every inch of its life, a turned down, stock GM 400 crank, 383 ... until it blew to kingdom come, after 13 years.

    That vehicle's latest 383, has a high dollar steel crank, amongst other high $ parts ... & I have maybe 500 miles on it since, 2009. Yikes.

    Hope that helps.
     
  27. jaw22w
    Joined: Mar 2, 2013
    Posts: 835

    jaw22w
    Member
    from Indiana

    Thanks! That is a good explanation. Learn something every day. I just never got into crank design to have heard the term. Racing, I once broke a stock 400 crank right behind #3 main. I also broke a high $$$$ 410 crank in the same place at about 8200 rpm. That one tore up a lot of shit.
     
    Montana1 likes this.
  28. Deuces
    Joined: Nov 3, 2009
    Posts: 17,695

    Deuces
    Member
    from Michigan

    Look into '70-'71 gmc or chevy pickups with a 350 4-bbl carb.... The blocks are 4-bolt mains with a forged steel crank.... And heavy duty "X" truck rods..... Allot beefier than car rods......
     
  29. Budget36
    Joined: Nov 29, 2014
    Posts: 2,308

    Budget36
    Member


    Good advice, but thinking I'd like to use what I have...hence my original question. Thanks
     
    Deuces likes this.
  30. MAD MIKE
    Joined: Aug 1, 2009
    Posts: 378

    MAD MIKE
    Member
    from 94577

    Fairly sure the Goodwrench 350 service replacement engines all use a nodular iron crankshaft.
    Cast<Nodular Iron<Cast Steel<4340.
    The cast steel crank is plenty strong for mild performance and midrange useage.
     
    Deuces and Budget36 like this.

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