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Technical 327 : Large vs Small Journal

Discussion in 'The Hokey Ass Message Board' started by Wyld Deuce, Feb 18, 2017.

  1. Wyld Deuce
    Joined: Oct 17, 2005
    Posts: 100

    Wyld Deuce
    Member
    from ...

    Aside from the obvious......
    What is the difference between the large and small journal engines?
    Is one better than the other? (performance, parts, size .....)
     
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  2. henryj1951
    Joined: Sep 23, 2012
    Posts: 2,310

    henryj1951
    Member
    from USA

    .....got busy had to answer the call BRB
    friction ,
    reciprocating weight ,
    lot of variances to rpms and intended use
    dang phone brb
     
    Last edited: Feb 18, 2017
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  3. Kan Kustom
    Joined: Jul 20, 2009
    Posts: 2,401

    Kan Kustom
    Member

    Calling Squirrel........ He knows these things.
     
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  4. From what little I have heard the small journal is supposedly the strongest & the heaviest,but I am no expert - The guys I thank are as knowledgeable as any is Squirrel & Beano. HRP
     
    Last edited: Feb 18, 2017
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  5. henryj1951
    Joined: Sep 23, 2012
    Posts: 2,310

    henryj1951
    Member
    from USA

    HRP is correct on the stronger crank , small journal also decreases the surface speed of the bearing and it a has a reduced negative torque that the large bearing does.
    might be worth 3-5 hp, but you will never see that on a dyno.

    If i was in the room with Jim and beano out of the 3 of us BOTH of them would still BE smarter than me.
     
    Last edited: Feb 18, 2017
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  6. finn
    Joined: Jan 25, 2006
    Posts: 649

    finn
    Member

    It's been a long time, but I recall that the early small journal 327s had a forged crankshaft, while the large journal cranks were cast.

    Overall crank strength may be similar though, given that larger journals generally mean more pin overlap.
     
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  7. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    I'm not so sure about that...
     
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  8. slowmotion
    Joined: Nov 21, 2011
    Posts: 3,130

    slowmotion
    Member

    I seem to recall certain M/P guys sought the small journal cranks for twisting those screamers into the twilight zone (& beyond). :eek:
     
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  9. What do you plan to do with this 327, if I might ask...Makes all the difference in the world. LOL
     
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  10. You know a lot more than your letting on~
    Am I right in thinking that tall the small journal 283 & 327's cranks were forged steel cranks? HRP
     
    Last edited: Feb 18, 2017
  11. No
     
  12. joel
    Joined: Oct 10, 2009
    Posts: 1,559

    joel
    ALLIANCE MEMBER

    There are large journal forged cranks (GM ), but Eagle is much more plentiful. It's tough to find as good small journal rods as large journal for the money. In the '60's I knew a couple of guys that had water leaks at +.060". AS stated above I think the main thing is bearing speed.
     
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  13. What do you want to do with it ? If you wanna say I have a 327 it don't matter. If you wanna swing it high in rpm's a small journal then.
     
  14. toxic waste
    Joined: Dec 18, 2011
    Posts: 374

    toxic waste
    Member
    from Iowa

    How much hores power are you wanting? It really don't make much difference.
     
  15. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 6,021

    56sedandelivery
    ALLIANCE MEMBER

    Most 283 and small journal 327 cranks were forged; the later 283's got cast cranks however. The large journal 327 used both cast and forged cranks; I have both in the garage. Holler if you need one. Guys used to use the large journal, forged, 327 crank, but have the rod journals turned to small journal size, thereby slinging lighter connecting rods, less rod bearing surface/speed, and a stronger bottom end was the purpose. But, in a street car, it makes NO difference at all. I am Butch/56sedandelivery.
     
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  16. Bearing surface speed is lower on the small journal making less friction for higher rpm's.
    That helps the 327 wind up to the sky if you can get the air to them! ;)
    Higher rpm's translates to more HP per cu. in.
    Plus the 327 has an ideal rod to stroke ratio (1.75) for lower piston side thrust, meaning less friction. That's why everybody likes them.

    That ought to stir the pot. :eek::D
     
    Last edited: Feb 18, 2017
  17. tb33anda3rd
    Joined: Oct 8, 2010
    Posts: 15,393

    tb33anda3rd
    ALLIANCE MEMBER
    1. Connecticut HAMB'ers

    283 cranks fit into small journal crank 327.
    DSCF4201.JPG
     
    Last edited: Feb 19, 2017
  18. 32v
    Joined: May 20, 2007
    Posts: 928

    32v
    Member
    from v.i.

    hmm, I have a nos gm 302 nitrated crank for sale if interested
     
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  19. Most of the small journal cranks did not have a drilled snout for a bolt to hold the harmonic balancer on. And a 283 crank will fit in a small journal block. the large journal block is practically the as a 350 block. Boring a small journal block past .030 is kinda iffy. I have several of both kinds of 327,s in my hoard. they aint for sale.
     
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  20. DDDenny
    Joined: Feb 6, 2015
    Posts: 13,086

    DDDenny
    Member
    from oregon

    I have an NOS oem nitrided small journal crank in my Nova 327 plus .040 as well as NOS rods.
    No they are not for sale.
     
  21. Wyld Deuce
    Joined: Oct 17, 2005
    Posts: 100

    Wyld Deuce
    Member
    from ...

    One day I would like to get one and rebuild it.....Stick into a hot rod that I do not currently possess.
    Daily driver mostly, not to mention the drag strip is only 6 miles away.
    I have a heavy foot and like to play. :D
    I've always known about the two models, just not the differences.
    I wasn't sure if it was anything like the 351c/351w scenario.
     
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  22. In that case, just build a more modern 383 and tell everyone it's a large journal 327.
     
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  23. henryj1951
    Joined: Sep 23, 2012
    Posts: 2,310

    henryj1951
    Member
    from USA

    ah yep.... 383
     
  24. southcross2631
    Joined: Jan 20, 2013
    Posts: 3,352

    southcross2631
    Member

    Raced both in Modified production . Put studs in the mains ,ran aluminum rods turned them both over 8 grand. GM cranks turned polished and balanced.
     
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  25. willowbilly3
    Joined: Jun 18, 2004
    Posts: 4,356

    willowbilly3
    Member Emeritus
    from Sturgis

    I always preferred the small journal. I have been told they all have steel cranks. Less bearing speed. Guy who used to build our roundy round dirt car engines only built small journal for that reason. The only negative, small as it might be, is that you can used a 4 bolt main cap block to build a large journal but that just a lot of smoke and mirrors people have been sold IMO. Never seen a well built small journal for a street car have lower end issues.
     
  26. You won't see a difference in performance between a big or small journal 327. The big journals came out in 1968 because Chevy had transitioned to big journal when the 350 came out. Most small journal 327 cranks were steel, some were cast. I have found the opposite to be true with the big journal stuff. Big journal 327 cranks are hard to find, especially steel, because by mid 1969, the 327 production was stopped, and it's applications were split between the 307 on the economy end and the 350 on the mid and high performance end. The 327 is one of my favorite small blocks because it does everything right. It's got decent torque, great midrange, and will rev to the moon. And on the big block side, the 427 is the same kind of animal, only meaner. It was like the stars were in perfect alignment when the 327 and the 427 were conceived. GREAT ENGINES.

    Sent from my QMV7A using The H.A.M.B. mobile app
     
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  27. Onemansjunk
    Joined: Nov 30, 2008
    Posts: 151

    Onemansjunk
    Member
    from Modesto,CA

    Butch/56sedandelivery is correct about turning the rod journals down on the forged large journal 327 cranks! Some would machine them off-center---"ECCENTRIC "--to increase the "THROW"--and-"STROKE ".Re-balancing was the KEY!




    Sent from my iPad using The H.A.M.B. mobile app
     
  28. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,545

    sunbeam
    Member

    Put a 327 crank in 400 block get the short stroke and 350 inches
     
  29. fatassbuick
    Joined: Jul 6, 2001
    Posts: 988

    fatassbuick
    Member

    Put a 283 crank into a 327 and you've got a 301 (basically, a 302 Z28 motor). Small journal is apparently easier to get the good stuff. The ratio between bore and stroke of this hybrid is considered perfectly square (old fart language) for torque vs RPMs, bleh bleh. Small has more balls.
    This is great thread, love this board for details.
     
  30. henryj1951
    Joined: Sep 23, 2012
    Posts: 2,310

    henryj1951
    Member
    from USA

    bore (4.00)x bore (4.00) x .7854 x cylinders (8) x crank stroke 3.00 =
    you do the math

    the old 283 turned into a ---___________<---
     

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