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Technical Flathead relief texture

Discussion in 'The Hokey Ass Message Board' started by Boden, Aug 23, 2019.

  1. Boden
    Joined: Oct 10, 2018
    Posts: 278

    Boden

    So I ported and half relieved my 1953 8ba block. I made my intake ports rough so the fuel tumbles in with the air. That what my boss said to do. It makes better atomization. I polished all the valves and all of that. Now I relieved it. But I was wondering if I should leave the relief rough or should I polish it out and make it smooth? And btw I will be using a 2 or 3 deuce intake with sharp high compression heads.


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    Last edited: Aug 24, 2019
  2. Casey Riley
    Joined: Jun 27, 2018
    Posts: 388

    Casey Riley

    I'm kinda thinking they will want to know kind of engine/manifold/heads you're working on.
     
  3. Boden
    Joined: Oct 10, 2018
    Posts: 278

    Boden

    Oh sorry. I didn’t even think about that. Haha


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  4. Seems like his post covered that:confused:.Flathead,2or3 deuce intake,sharp heads.
     
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  5. Casey Riley
    Joined: Jun 27, 2018
    Posts: 388

    Casey Riley

    Yes, now that he edited the post to include it...
     
    Last edited: Aug 23, 2019
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  6. Mike VV
    Joined: Sep 28, 2010
    Posts: 1,554

    Mike VV
    Member
    from SoCal

    No...he really didn't say what the block is...but we can guess by his avatar..!

    I port overhead valve heads, have for 30 or so years. Only done two flat head blocks.
    On the first, I left the surface smooth, but not polished. The second, years later, as I do in over head intake ports, is to let a carbide cutter kind of lightly bounce on the surface, making tiny little craters. That is, guide the cutter over the surface after final shaping, but do not use any downward pressure on the iron surface.

    What your "boss" said is sorta correct. While it does not make the "atomization" better...it does help to make sure that at low air/fuel flow speeds (low rpm), fuel droplets have a tendency to stick to polished or smooth surfaces, then when you hit the throttle, the big drops are forced off of the surface by the new higher flow speed and end up in the chamber as BIG drops...not good.
    You want the smallest droplets as you can get. This is why modern fuel injection is good, the drops are VERY small. Small droplets ignite easier/faster than larger drops to make better power.
    Like 60 or 40 grit sand paper surface vs. 600 grit paper surface. 60/40 grit surface good, 600 surface, not so good.

    Mike
     
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  7. Boden
    Joined: Oct 10, 2018
    Posts: 278

    Boden

    Ok. Thank you very much.


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  8. flatheadpete
    Joined: Oct 29, 2003
    Posts: 9,408

    flatheadpete
    Member
    from Burton, MI


    Great explanation!
     
  9. polish the exhausts, leave the intakes rough
     
  10. Sorry Casey,old eyes didn't notice.
     
  11. I would think that you want the relieved portion of the block (down stream of the valves) smooth (if not polished). It is part of the combustion chamber and you don't want any hotspots. My flathead was factory relieved...and it's smooth.
     
    Last edited: Aug 24, 2019
  12. alchemy
    Joined: Sep 27, 2002
    Posts: 14,089

    alchemy
    Member

    Mike and Carl are talking about the ports. The question was what to do with the relieved area inside the combustion chamber? I'd say make it smooth. Less chance for any build up of carbon. The underside of the heads should be nice and smooth too, if you want to go to the work.
     
    anothercarguy likes this.
  13. Relieved area should be smooth to prevent carbon build-up and hotspots.
     
  14. x2 on polished combustion chamber
     
  15. On a street flat head you probably will never tell the difference. But in your head you will be convinced.
    Enjoy
     
  16. bored.030.JPG
    Factory relief on a 1947 truck flathead.
     
  17. Casey Riley
    Joined: Jun 27, 2018
    Posts: 388

    Casey Riley

    That's the most important part.
     

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