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Thread: Ex.Chamber Science

  1. #1
    Team Member Tomtall's Avatar
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    Arrow Ex.Chamber Science

    Gotta thank Jeff Lytle for finding this one.Cool site Jeff! http://kawtriple.com/mraxl/expansionchambers.htm

    Last edited by Mark75H; 03-23-2005 at 06:57 PM.
    TOM L.

  2. #2
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    Default Good illustration Gentlemen

    But I can't work out why his reeds are chuffing at the end of the inlet stroke, give me that M6 spanner I want to have a look at them.

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    Team Member kws's Avatar
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    somethings just make you hmmm
    makes me wonder why they called them expansion chambers and not a packing chambers

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    Sam Cullis Mark75H's Avatar
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    The term "expansion chamber" actually pre-dates the late 1950's MZ tuned pipes. I was quite stunned to see it in literature from the early 1950's. At that time it simply refered to a closed area for exhaust gases to expand in. It would be very interesting to learn how the phrase "expansion chamber" came to be associated with tuned pipes .... could have been a misnomer by some boat racer or perhaps Carl Kiekhaefer himself. I think a query to Mssrs. Strang and Rose is in order.

    The first outboard I've seen with closed end pipes is the 1961 Carniti V-4 500cc racer, followed by Königs a year or so later .... after 2 years of the Carniti dominating 500cc racing in Europe. I think Carniti took the 500cc World championship 2 years in a row before König switched to loop charging and expansion chambers. König's switch to loop charging is what drove Christner to produce the Quincy Looper. You have to fight fire with fire sometimes.
    Since 1925, about 150 different racing outboards have been made.


  5. #5
    Team Member kws's Avatar
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    i think i read somewere the germans played with expansion chambers in the 20's. but i could be very wrong lol have slept many times since i read that.
    but one thing is for sure that is a great illiustration
    if a picture is worth a thousand words, a moving colorized picture might be worth 10,000 words lol
    Last edited by kws; 02-14-2005 at 10:15 PM.

  6. #6
    Sam Cullis Mark75H's Avatar
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    A German developed loop charging in the 20's. Expansion chambers were also invented by a German, but it was the late 1950's.
    Since 1925, about 150 different racing outboards have been made.


  7. #7
    Sam Cullis Mark75H's Avatar
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    The basics of how an expansion chamber works:

    The first section works the same way an open megaphone works:
    Exhaust bursts out into the pipe when the exhaust port opens, then
    it progresses thru the pipe with that initial burst of speed continuing
    beyond the length of pipe necessary to clear the cylinder of exhaust ...
    actually pulling fresh charge from the crankcase up into the cylinder ....
    sometimes with even enough force to reopen reed valves that have
    sprung shut.

    The middle section of the pipe is just a length of pipe to get the timing right
    for the grand finale ... at the end of the pipe the sound wave echos off
    the final cone .... heading back to the exhaust port and sheparding some of the
    gasses in the pipe with it. An open megaphone tends to over scavenge
    the fresh charge out into the megaphone or at least the header leading to it;
    so does the first cone on an expansion chamber. The more or less hard reflection
    from the final cone pushes the over scavenged fresh charge back into the
    cylinder just before the exhaust port closes (but well after the transfer
    port has closed).

    One more part: The "stinger", bleed resistor or muffler
    the last section of an expansion chamber is a restriction that further increases
    the pressure in the pipe. The cone sections of the pipe work so well that
    the expansion chamber actually can release the exhaust and pull in the fresh
    charge while the average pressure in the pipe is higher than atmospheric pressure.
    This allows that final jamb back of pressure into the cylinder before the
    exhaust port closes to significantly increase the cylinder pressure ....
    just like a supercharger.

    As long as the average flow out the bleed resistor is equal to the total
    flow out the exhaust port you can continue to increase the average
    pressure in the pipe and the motor. Too little flow from the outlet and
    you will cook the motor ... too much flow and you are giving away free
    horsepower .... it is a fine balance that depends on variables from the
    carb to the prop.

    The smallest usable outlet is the one that allows the motor the most rpm
    your prop and set up allow, but no more .... this will yeild the greatest power. Change
    props, motor height, angle, significant weight of driver and you may go over
    the edge and not let enough exhaust out .... cooked motor!

    Attached Images Attached Images  
    Last edited by Mark75H; 02-21-2005 at 11:07 AM.
    Since 1925, about 150 different racing outboards have been made.


  8. #8
    Sam Cullis Mark75H's Avatar
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    The length, size and taper angles of each part affect the way the pipe causes
    the exhaust sound waves to affect the motor.

    Early expansion chambers had longer mid sections and shorter
    final cones. It was soon learned that the short final cones
    cause the pipe to work well at only the very highest rpm. A change
    was made that extended the effective upper rpm range where
    the pipes worked .... longer final cone, slightly shorter middle.

    The next major change was to allow the pipe's whole length to
    be changed by having the pipe slip over the header pipe. This allowed
    the pipe to have 2 major rpm range's where it worked well instead of
    one.

    Non-sliding pipes will work dramaticly only in the single rpm range where
    the length agrees with the motor rpm .... maybe 9,000 to 11,000 for a
    Konig, Konny, Rossi or Yamato PRO motor. Allow the pipe to slide out to
    a longer length and it can also work at 6,000 to 8,000 when it is long.
    Attached Images Attached Images  
    Last edited by Mark75H; 02-21-2005 at 12:00 PM.
    Since 1925, about 150 different racing outboards have been made.


  9. #9
    Sam Cullis Mark75H's Avatar
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    Sliding pipe:
    Attached Images Attached Images  
    Since 1925, about 150 different racing outboards have been made.


  10. #10
    Sam Cullis Mark75H's Avatar
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    Oh my you say .... won't the exhaust escaping from the slip
    joint affect the operation? Well, it could if it was a very sloppy
    and loose fit, but keep it tight and you can easily make up for it
    by reducing the exhaust stinger size or increasing the stinger length
    a little bit. The exhaust escaping the slip joint is normally of no
    concern at all.

    The exhaust outlet doesn't even have to be at the tail end of the
    final cone. GoKarts use an opening in the middle of the middle section.
    Some special high ground clearance motocross bikes used a snail
    shaped expansion chamber with the stinger off the middle of the
    middle section. My brother saw one of those 25 years ago and made
    one himself and it worked as good or better than the original expansion
    chamber for that bike.
    Since 1925, about 150 different racing outboards have been made.


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