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Weird flathead relief

Discussion in 'The Hokey Ass Message Board' started by olskool34, Jun 14, 2012.

  1. olskool34
    Joined: Jun 28, 2006
    Posts: 2,458


    I just got to taking my 46 59A flatty's heads off to inspect for wear and this is what I found. Releived on the intake side only, intake valves say Ford on them. Very clean inside. Block has traces of maroon metallic paint on it. Bore is stadard, I am going in to look at the valvetrain next. Why would someone relieve the itake only?

  2. paulie_boy13
    Joined: Mar 1, 2005
    Posts: 269

    from NC

    I would suspect the thinking was to get the tumble more over the piston. instead of detonating with the mix mostly on the edge as Ive seen in "smarter guys than me" flow charts.

    Hard to tell on my phone but is the exhaust valve bigger than the intake?
  3. Rickybop
    Joined: May 23, 2008
    Posts: 6,963

    from Michigan

    Better flow yet still retain as much compression as possible?
  4. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    from florida

    That is odd. Here is a 46 block with the usual factory relief done to it.



  5. That is a type of relief that was used by Harley Davidson when modifying their flathead V-Twins. I have seen drawings of this type of relief.

    This idea was picked up by flathead folk, the idea being, as suggested already, to increase intake flow but to retain as much compression as possible.
  6. CheatersPete
    Joined: Sep 25, 2002
    Posts: 1,270


    Here is my current project, done the relief last week...

    I have done this to match the Edelbrock block letter heads...

    Attached Files:

  7. olskool34
    Joined: Jun 28, 2006
    Posts: 2,458


    That makes sense I guess. Thanks for the responses.
  8. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,682

    Bruce Lancaster
    Member Emeritus

    I have seen one such intake-only relief, on a circle track engine in Pennsylvania in late 1960's.
    Compression is probably the actual explanation for "why", but there may be more.
    Flatdog once told me he had been studying exhaust flow and had observed that the exhaust flowed mostly on the INTAKE side of the chamber, tucking into the exhaust valve kind of sideways!
    This is why you need a good parapsychologist on call when studying flatheads...
  9. dan c
    Joined: Jan 30, 2012
    Posts: 2,189

    dan c

    mike davidson, the aussie flathead guru, claims the intake-side-only relief is the hot setup. but didn't barney navarro's heads put a deeper relief on the exhaust side?
  10. There are two basic schools of thought on 4 stroke engine breathing, one school believes that you need bigger intake valves and better intake porting to get as much mix into the cylinder as possible. Those are the fellas running 800 cfm carbs in a situation where a 600 cfm carb would produce proper results.

    The other school of thought is that if you have clean cylinders you don't need as much intake volumn. They also believe that it is easier to get mix in then to get mix out. Those are the fellas running the smaller carb and getting the same or better results than the big intake guys.

    I think that different engines bring their own problems but the answer to some fellas (think old timers) is concentrate on the exhaust side and others will concentrate on the intake side.

    I have heard from a lot of flathead guys that they are weakest on the exhaust side, thus splitting the center port etc.

    The engine in the original picture looks to be relieved wither at the factory or by someone who is more meticulas than your average backyard builder.
    Last edited: Aug 13, 2012
  11. I have seen a couple of blocks with the single side relieving. I think it's factory, but for what I have no idea.

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