Non-File fit vs. file Fit rings, Whats the difference?

Discussion in 'Engine Topic' started by probizjudi, Oct 24, 2005.

  1. probizjudi

    probizjudi Veteran Member

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    In response to my post re info about 383 crate engines, the one we were interested in used non-file fit rings and the person who responded suggested using file-fit rings. Pls educate me--whats the difference and is one better than the other and why?
    Thx!


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  2. 78LT383

    78LT383 Veteran Member Lifetime Gold Member

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    Non-file fit rings are supposed to fit when installed in a nominally sized bore. So, if you have an exactly 4" or 4.030" bore, for example, these are supposed to already fit perfectly. You still need to check them, but that's the idea. They're not bad for situations where you're working with standard bore sizes from GM, or you happen to have exactly nominal bore size.

    File-to-fit ring sets allow you to correctly fit the rings to the bore. With high performance engines, you should always have the pistons in-hand at the machine shop so that they can bore and hone the engine to the exact clearance based on actual measurements from the individual pistons you'll be using. This custom fitting of each piston to the block provides ideal conditions that promote maximum life for the engine and optimum conditions for the rings. However, the size will not be exactly the nominal dimensions- such as 4.030" for a .030" overbore 4" bore engine. File-to-fit rings come with virtually zero gap so that you can file them by hand to achieve the perfect fit to your exact bore. This is a no-compromize solution to provide a perfect fit.

    So, if you're in a hurry or you have already cut other corners such as not honing the block with a torque plate, non file-fit rings are probably not going to hurt anything. These are what GM uses, and they routinely last 100,000+ miles. However, if you're willing to do a little work for more power and you've gone the extra mile everywhere else, file-to-fit rings are worth a few HP.
     
  3. Larry Tinker

    Larry Tinker Veteran Member

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    and the 'file to fit' allows you to taylor your rings to you use/set-up. if you are going to run nitrous, the gap may need to be increased to compensate for the extra heat and pressure. the rings will expand more with the extra heat. you don't want the ring gap to 'zero-out' 'cause then they have nowhere to expand except into the cylinder wall. causing major failure. seems like my file-to-fit rings came with a chart to help you with the proper gap for your bore and nitrous use.
     
  4. 80'427

    80'427 Veteran Member

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    Speed pro has a chart in there catalog that lists usage and suggested end gap. File fit are a bit more custom and allow you to your exact useage and exact cylinder so you are blue printing each set of rings to each cylinder. Non file fits typically have a overly wide gap to prevent butting in nearly any application and with some cylinder variation. The problem is they give up a bit of HP because of the cylinder leakage. I use the file fits if HP is important and in most stock type just use the standard ring.
     
  5. rustbucket79

    rustbucket79 Veteran Member

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    If you use a hypereutectic piston in a high performace application the standard gap rings require additional grinding to prevent butting. File fit rings are a final little tweak you can do to maximize engine efficiency and with most ring sets you only end up closing the gap maybe .002 to .004 on a N/A application, cast or forged piston. I would look for an engine that was torque plate honed long before file fit rings.

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  6. probizjudi

    probizjudi Veteran Member

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    Thx for all the good info! u really helped me understand about the rings.

    But just to clarify more about the car and set up:
    We are looking for a 383 crate engine/425HP or so - Car will be used mainly as a "cruiser" w/an occassional run at the track. Not a daily driver either.

    So from what u all said sounds like we can go w/the non-file rings for our intended use. Any other comments? Thx again!


    ------------------
    70 Camaro 350 TH350; 2bbl "work in progress"! Stay tuned for updates!
    Update(s): 3.42 posi finally installed!

    Look Ma! No interior!
    Look Ma! rear susp. done, rear drum brake upgrades, Classic shocks installed!

    Tires/Wheels have arrived! TT2's 16X7, & 16X8
    Front susp. work finally done! Redoing front disk brakes w/all new parts! Steering box rebuilt!
     

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