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Internally vs. Externally balanced...

Discussion in 'The Garage' started by fortcollinsram, Apr 18, 2002.

  1. fortcollinsram

    fortcollinsram 1/2 ton status

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    What is the difference? I know you need different flywheels but why? What are the mechanical and physical differences in the engine?

    Thanks,

    Chris
     
  2. Sandman

    Sandman 3/4 ton status Author

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    Well, internally balanced engines do not need a balanced flywheel. I believe that these are all small blocks but not the 400. I am not so certain about the big blocks but I do know that the 454 is not internally balanced and needs a balanced flywheel. So it works out that the flywheel from a 454 and the 400 are interchangable. Hopes this helps some.
     
  3. TopOff

    TopOff 1/2 ton status

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    What about a 383 that is internally balanced?
     
  4. 70~K5

    70~K5 1/2 ton status

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    NO! NO! NO! A 454 and sb400 use diferent flywheels.
     
  5. gtkustoms

    gtkustoms 1/2 ton status

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    topoff

    if the machine shop internally balanced the 383 then you would use parts from another internally balanced engine like the 350.......would require parts like the damper, flexplate ie..

    but if you just threw in the 400 crank into the 350 block then you would have to use the 400 damper and flexplate
     
  6. marv_springer

    marv_springer 1/2 ton status

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    An internally balanced engine uses a flywheel and damper that ARE balanced (no imbalance). So the rest of the rotating/reciprocating assembly is balanced to the best condition (which by the way is a compromise at best) with the counterweights on the crank.

    An externally balanced engine uses a flywheel and damper that have "built in" imbalance to work in conjunction with the counterweights on the crank to bring the whole assembly into optimum balance... So this is why the bolt pattern will be skewed so that the flywheel can only be installed one way.

    BTW, the only way a "perfect" balance could be achieved is with counter rotating shafts going at 2 times crank speed.

    Marv
     
  7. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Didn't Chevy do the counter rotating balance shafts on the newer 4.3 V-6's? A 90 degree V-6 is a pretty unblanced motor at the best of times...

    Rene
     
  8. marv_springer

    marv_springer 1/2 ton status

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    Yes, Chevy tried a version of the counter balance shafts with the 4.3.

    And yes, an EVEN fire 90* bent six brings on balance problems. In fact the stock balance was intended to send the majority of resulting imbalance forces into the horizontal plane so that the motor mounts would hopefully soak it up.

    Also why all the "full race" competition 90* V6's used a "straight pin / odd-fire" crank. This crank is balanced as easy as a V8 because of it's "common pin" crank journals.

    Whew... got off into this a little more than I maybe should've... Sorry to be so wordy!

    Marv
     
  9. TopOff

    TopOff 1/2 ton status

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    Now that you put it like that, I bought a 400 flexplate, and 400 dampner, so I suppose I should buy a 400 flywheel. /forums/images/icons/frown.gif

    Thanks for the information.

    Now I understand how a 350 unbalanced dampner and unblanced flywheel would WORK!
     
  10. Sandman

    Sandman 3/4 ton status Author

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    NO! NO! NO! A 454 and sb400 use diferent flywheels

    Thats interesting to hear because I have switched them around with no trouble. I took out a 454 out of my chevelle that had a manual and put in a 400 that was in front of an automatic. I know other people that have done the same. What are the differences? I wouldnt want to be giving out bad advice. Thanks.
     
  11. chevyracing

    chevyracing 1/2 ton status

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    <blockquote><font class="small">In reply to:</font><hr>

    Now that you put it like that, I bought a 400 flexplate, and 400 dampner, so I suppose I should buy a 400 flywheel.

    <hr></blockquote>


    So, are you putting a flexplate and flywheel on this engine. If so, please post pics.

    John
     
  12. TopOff

    TopOff 1/2 ton status

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    Oops, I really need to start proof-reading my posts.

    I have been running the 383 for over five years now, with a TH350. I have the trans and x-fer (203) needed to convert it to a manual. My last debate is to wait and get the doubler and a hydraulic setup.

    TIA
    TO
     

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