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    • CommentAuthordavid
    • CommentTimeJan 5th 2009
     
    Over the past few weeks I have been sketching engines and engine parts.
    Some are flat head and some are overhead valve.
    What are the advantages of flat head verses overhead valves?
    •  
      CommentAuthormonighan
    • CommentTimeJan 6th 2009
     
    Overhead engines develop more power because they breathe better because the valves are over the piston,higher compresion ratio,better combustion chamber. Flat heads of course have a much larger combustion chamber (lower comp. ratio) and don't breathe well because of the extra distance the fuel air mixture has to travel over the top of the cylinder.
    • CommentAuthorkuhncw
    • CommentTimeJan 6th 2009
     
    I have an old text book "The Gasolline Automobile" from the late 1930s. Per this book, the flat head (L head) engine minimizes the number of mechanical parts in the valve train. The overhead valve arrangement (I head), with valves above the piston lends to a more compact combustion chamber. Combustion chamber wall area is reduced for a given combustion chamber volume. This would help reduce heat rejection to the engine coolant. The book also mentions T head, F head, and H head valve arrangements. The F head has one valve in the head and one in the block.

    Regards,

    Chuck Kuhn
    • CommentAuthordavid
    • CommentTimeJan 10th 2009
     
    My engines have never had more than 6:1 compression. I probably should increase that a little.
    I like the simplicity of the flat head but understand the extra heat loss in the flat head.
    My long term project goal is to pick a design, build it, reduce the size, build it until it won’t run.
    I suspect I will have better luck with overhead valves.
    I know there are small engines out there. What is your smallest 4 cycle bore stroke? How does it run?
    • CommentAuthorkuhncw
    • CommentTimeJan 11th 2009
     
    My comment regarding heat loss in the flat-head design was aimed at full size engine practice. In model engines, I wouldn't be too concerned about heat loss.

    George Luhrs builds the smallest engines I know of. He built a 0.125 inch bore single cylinder.
    ->link<-

    In my shop, 0.750 inch dia bore is small.

    Good luck with your project. Please keep us informed.

    Regards,

    Chuck
    •  
      CommentAuthormonighan
    • CommentTimeJan 11th 2009
     
    Has anybody ever tried to supercharge a single cyl engine under say .25'' bore? I'm sure turbo charging wouldn't work because the exhaust from such a small cu. in. would barely turn it. Excluding the small block V8's.
    I've seen hand built single cyl garden tractors engines used for pulling contests, but they had a 5-6''dia. piston. Of course this doesn't pertain to this subject.
    • CommentAuthorrick d
    • CommentTimeJan 12th 2009
     
    You can try this web site. ->link<-
    • CommentAuthorrick d
    • CommentTimeJan 12th 2009
     
    This goes right to the pagehttp://www.edstroementerprises.com/jep/index.htm
    • CommentAuthordavid
    • CommentTimeJan 12th 2009
     
    In 2007 at NAMES there was a large central display of George Luhrs engines, it is in the Events/Shows area. The engines were so small and the extra parts were perfect.
    When I was working on air powered engines, .125 bore was as small as I could get to run good. I made a few .093 bore engines but never got one I can say ran well or built enough confidence to try .062.
    I like taking steps with a project in site. Design and techniques improve on each build.
    Based on my other engines I think my present equipment and my experience I doubt I can build smaller than .312.
    I think the this series will be.75, then .625, .5, .375, .312, looks like a long time.