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  1. #106
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    Click image for larger version. 

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ID:	371186It's amazing how this chest makes enough bottom end to make a triton tr 20 come out hole much better than a 250 pro xs and still push the boat over 80 with full tournament load? There may be something to gain by stuffing and spacers??

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  3. #107
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    ttt , Happy New Year

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  5. #108
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    Quote Originally Posted by Nosubforcid View Post
    Well the theory that all cylinder filling is the result of piston displacement and pressure in the crankcase is pretty outdated. That theory held that cylinder filling is simply a one to one volume exchange. The problem is that theory doesn't allow for the time lag to get the charge moving, and since charge mass per stroke is essentially constant with rpm so is the time lag. This leads to progressively poorer performance as rpm increases and this time lag becomes proportionally larger with respect to the time available to fill the cylinder. Current two stroke theory holds that a properly evacuated cylinder is not just one that is blown down to ambient pressure but one that is pulled below ambient pressure by the momentum of the exhaust rushing out the port. This low pressure wave is what starts the fresh charge moving in the transfers(generic use meaning all intake ports) before any positive pressure in the crankcase could ever hope too. Similarly the columns of charge in the transfers have mass and correspondingly momentum so they do not stop flowing as soon as the cylinder is"full" or back to ambient pressure. The charges continue to stream from the transfers and collide with each other producing an area of localized high pressure while some flows out the exhaust port. This charge that flows out the exahust is to a great extent rammed back in to the cylinder by the rising pressure in the exhaust tract either from an adjacent cylinder blow down in our V6s or a reflected wave in the expansion chamber in other applications. This combination leaves the cylinder "overfull" or supercharged above ambient pressure something a high crankcase pressure design could never achieve due to lack of crankcase volume.
    This is great post made 15+ years ago and 2 stroke theory is still evolving on this line of thinking. The only problem is the only advances being done and put to practice are in Small R/C nitro eng today.
    The understanding of this is evident in the porting and flow control used in the newest eng.
    Take time and read this post and try to understand what is being explained.
    Thanks FMP for bringing this to the top for a reread.

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  7. #109
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    That exhaust looks somewhat like what Junior and Del Eaves used to do for us drag racing but a little more curvy.
    We needed bottom end also.


  8. #110
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    Here isClick image for larger version. 

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ID:	396302 how they did it back in the day and it still works


  9. #111
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    A different angle on another one I've done. Real similar to what Eaves was doing. The main difference is I am blending the angle in the space between the ports and Eaves was leaving an edge. I think I like Eaves way a little better as it should have a little better velocity and help prevent flow from sticking to floor and help send it over the next guy in line. I think on next build I'm gonna try it that way and see how it does. You are right it does make a surprising amount of low/ midrange power. BTW Eaves was the man!

  10. #112
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    I think someone needs to make a stacker from a v6 or even 2x 3 into 1 collector

  11. #113
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    Very interesting and thought provoking thread.
    There's a lot to be taken from this even though i,m building a V4 trying to get a strong 6500 RPM not for all out speed.
    Just a strong reliable lake motor.
    How does polished exhaust (mirror shine) compare to a smooth finish?
    Longer for carbon to bind to ?
    Faster flow ?

    I love my Bikini

  12. #114
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    I like to polish mine mainly so carbon doesn't stick and restrict/slow flow in the long run. I feel a not so slick finish actually flows better and would be great on motor that was constantly coming apart and getting cleaned.

  13. #115
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    Quote Originally Posted by powerabout View Post
    I think someone needs to make a stacker from a v6 or even 2x 3 into 1 collector
    How many more would you like us to make before you notice ....


  14. #116
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    Whats different with the powerhead?
    The exhaust is longer than stock, more low end..is it for waterskiing?
    Lol
    Last edited by powerabout; 01-06-2018 at 08:52 AM.

  15. #117
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    Stock MontyMan "pro/gas" powerhead ...

    This is the "waterski" 6 guzinta 1 pipe ...


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  17. #118
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    Quote Originally Posted by spybot View Post
    Very interesting and thought provoking thread.
    There's a lot to be taken from this even though i,m building a V4 trying to get a strong 6500 RPM not for all out speed.
    Just a strong reliable lake motor.
    How does polished exhaust (mirror shine) compare to a smooth finish?
    Longer for carbon to bind to ?
    Faster flow ?

    On the cc volume, one size don't fit all. If your not gonna turn crazy rpm, a tighter cc is usually beneficial. You can widen your ports in cylinders to get more flow to get more charge in cylinder and increase cc pressure to bring velocity back up at low rpm. It'll also allow the cc pressure get below atmospheric pressure sooner at bdc and allow reeds to open sooner to maintain flow through crankcase to cylinder before transfers close, then fill cylinder volume more efficiently once ports close. At really high rpm levels you can get to a point of deminishing returns where the extra pressure causes more drag than you are gaining from the stuffing. Also you can lose low end power if your cc pressure is more than needed and allows too much charge to escape through exhaust port at low rpms.(usually the case with high blowdown degrees between exhaust port and transfer openings and a strong scavanging exhaust set up). So in a nut shell you'll need to experiment with your particular engine/porting design.
    Last edited by FORBESAUTO; 01-06-2018 at 08:21 PM.

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  19. #119
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    Quote Originally Posted by Chaz View Post
    Stock MontyMan "pro/gas" powerhead ...

    This is the "waterski" 6 guzinta 1 pipe ...

    Chaz, can you build me one of those mids for my bass boat? That'd be cool as crap to be at the landing waiting on your flight in a tournament with set up!!

  20. #120
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    Thats way way longer than stock, like has doubled the length of the exhaust.
    I wonder how that looked on the dyno compared to without it?
    Stock has nothing under the adapter as the collector is in the middle of the case not at the bottom.
    Last edited by powerabout; 01-06-2018 at 09:43 AM.

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