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  1. #46
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    This is a 1cid eng making 8+HP at 26000RPM on 60% nitro.
    This is just a case study as it is much cheaper to burn up this little eng than a 2.5 V6. LOL
    The next step is installing a Heimholz resonator in front of the cab to get it all in sink.
    There is no bottom end with this setup.
    this eng turns a progressive pitch prop with 4" lead in and 7" cup with a 5.8 average pitch.
    Runs at a little over 90mph in racing trim in a 3 point hydro.
    will run faster in a strait line loosened up. some where over 100mph
    This was on a bet that a two stroke eng would not start yet run with no intake valve at all.
    I have spent many hours and years studying two stroke theory and application with these small engs.
    Thy are a great test bed for applied theory.
    I am starting a 2.5 Merk build up to try some of what I have found with my testing.
    If you notice I had to put my fingers on the intake and ex to stop the eng.
    So what dose this demonstrate about crank compression?
    Any thoughts?

  2. #47
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    Quote Originally Posted by dwilfong View Post
    This iinterested a 1cid eng making 8+HP at 26000RPM on 60% nitro.
    This is just a case study as it is much cheaper to burn up this little eng than a 2.5 V6. LOL
    The next step is installing a Heimholz resonator in front of the cab to get it all in sink.
    There is no bottom end with this setup.
    this eng turns a progressive pitch prop with 4" lead in and 7" cup with a 5.8 average pitch.
    Runs at a little over 90mph in racing trim in a 3 point hydro.
    will run faster in a strait line loosened up. some where over 100mph
    This was on a bet that a two stroke eng would not start yet run with no intake valve at all.
    I have spent many hours and years studying two stroke theory and application with these small engs.
    Thy are a great test bed for applied theory.
    I am starting a 2.5 Merk build up to try some of what I have found with my testing.
    If you notice I had to put my fingers on the intake and ex to stop the eng.
    So what dose this demonstrate about crank compression?
    Any thoughts?
    so all the hobby engines are now sold without a rotary valve?
    Anyway everybody will be very Interested what you can come up with in an engine we can all relate to.
    Last edited by powerabout; 06-24-2014 at 02:51 PM.

  3. #48
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    No this was the first time it was demonstrated that it was possible.
    No one ever tried it because all thought it would not work.
    This was just a demonstration to show what is true and what is myth.
    this all goes back to what we all thought about a two stroke eng.
    Every one uses the theory that the piston dose all the work of moving the air threw the eng.
    I have modified my eng to remove as much of the sleeve and as much of the piston as possible from the case.
    I other words I have taken the piston PUMPING out of the equation in how I see the eng working.
    Hard for most to imagine this as you have always bin of the under sanding of the main stream of two stroke theory.
    Now try to wrap you head around a piston moving up and down 433 times a second. That is how many times it happens at 26000 RPM.
    Now imagine the air making this long trip up and down and all around at that speed.
    Puts a different light on what is really going on in side the case now dose it not?

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  5. #49
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    Thanks for the repost. Good reading.

    Rock
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  6. #50
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    I cant see how the piston pumping can be taken out as both sides of it are pumping as long as its going up and down

  7. #51
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    As I see it you are still relying on piston pumping just not crankcase compression held back by a valve. The compression in the crankcase is held in by velocity of the charge through the carb which is why it only makes power at high RPM. I would guess if the intake runner was smaller and or longer it would make power at a lower RPM. An expansion chamber would also help a bunch. If you want to remove crankcase pumping, you need to feed the carb directly into the intake port, isolate that port from the crankcase, vent the crankcase to atmosphere and find a way to oil the rod bearings. Then you would have a 2 stroke that was fed purely by charge velocity. I expect it would take a very high RPM to get it to start if at all.

    I would like to thank everyone that has contributed to this thread as I am looking at 2 strokes with a much better understanding of how many things come together to set the personality of the motor.


    98 Laveycraft Sebring 20.2 Tunnel 280 "catchin" motor. 90s? It's enough for me!

  8. #52
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    I have looked at the new small two strokes that use a stratified intake system.
    thy have a two barrel carb on them and open the second barrel to feed air directly into the transfer ports.
    This is done to lean the mixture with no added fuel. This design is to meet EPA emissions regulation on small eng.
    This will also be explored with a small eng with the second barrel adding fuel also.
    I have a suspition this will cure the low end power problem.
    Running the fist stage on the disk valve and then opening the second stage strait to the transfer ports.

  9. #53
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    Great discussion! I agree with lu2gofast. Gary
    "12" Super Lite Tunnel (11') "88" 25 Yammy twin carb "BANANA SPLIT"
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    "Too much is never enough" Keith Richards " Dreams become reality via hard work and perseverance" G.A.Carbonneau

    "This coming from an old man that strapped two bananas together, hung a motor on it and calls it a boat" XstreamVking

  10. #54
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    Absolutely interesting Thread, LOVE it.
    Glastron GT 150 W OMC 140
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    I know two things that are infinite, the Universe and Human's Stupidity, although I am not sure about the first one.

  11. #55
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    I would think that at this point people would have found an atleast close to optimum primary compression ratio for our type of engines. Of course each variation of engine would prefer a little different ratio but atleast you'd have somewhere to start. I'm sure that the experts have it figured out for the type of engine that they specialize in.

  12. #56
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    It's all about kinetic energy. Once that airflow is moving it keeps going.

  13. #57
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    Gordon Jennings describes a generator with direct crankcase inlet in his book The Two Stroke Tuner's Handbook.

    Some Caille racing outboards in the 1930's used carb bypass inlet and racers experimented with additional reed inlets directly over the transfer ports back in the 1950's.

    Everything old is new again.

  14. #58
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    In the late 1950's Charlie Strang hand carved out a worn out Mark20H crankcase die to make a special tight crankcase. It was only legal in the all out alcohol racing classes (might have become a Stock part later) ... but it provided NO power increase so it was dropped. Hop up shops sold all manner of crankcase stuffers.

    In the end it looks like crankcase volume is only something to be concerned about if its really in excess. Any reasonably tight crankcase is as good as its going to get.

  15. #59
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    Quote Originally Posted by racer View Post
    They also are installed into the same sled so they know exactly what the engine will be doing on an outboard they have to be able to work in a much larger area so the tune is much different. This is one reason hotrods are built for specific use and obtain more power per inch than production.
    Bingo!
    O/B's are way different than anything commonly seen stated as a bench mark for power.

    To validate Al's point, take a full zoot 2.5 off a 500 lb A Bote and screw it on a tournament loaded bass boat and see how it does.
    According to many these applications are the same correct
    It would take a tiny wheel to get the tournament boat on plane and would surely come back on thew end of a rope.
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.



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  16. #60
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    I think I read on here one of the merc guys who experimented with primary compression said too much of it is not a good thing for rpm. Cant remember who it was.
    Quartershot T-3R 15" E-Tec 1.62 sportmaster


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