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Who Wants MAC Products Aluminum 1/2A Tuned Pipes?

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Who Wants MAC Products Aluminum 1/2A Tuned Pipes?

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Old 05-11-2015, 10:53 PM
  #76  
Pond Skipper
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For the Cox engine I am at the stage where the next step is to file the the top of the exhaust port at and angle and raise the port about .5mm to allow more boost into the cylinder.

I have a single bypass port cylinder in the mail coming from Portugal - if it is what I expect there will also only be one exhaust port from the photos it appears to be the case.

Here is the parts description:

Cylinder, Piston, Rod Assy Kyosho 049-1477 Cox f1 LARROUSSE ferrari F189 Single Bypass


If that doesnt pan out I have a cylinder picked out to mod it has two bypass ports and two TD style exhaust ports a non SPI
Here is the cut pattern will mod only one side facing the pipe the other side will be blocked off.







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Old 05-12-2015, 12:16 AM
  #77  
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I have also noticed when the pipe starts to function it acts like a pump drawing more fuel air thru the carb. The NV setting on pressure has a small window from sweet spot.
Yes with boats all mechanical bugs / weak system components have to be worked out. I have ran mono's and outriggers on TD's and Queen Bee's. The TD's had more top
end speeds but the QB had a more robust crank case and could handle the Dumas 1/2A flywheel for more runs before over time it would waller out the aluminum crank case.
I had planed to use a bronze bushing but never sourced the part and drill bit size.The flywheel is a bit heavy I wanted to fabricate a lighter one. The surface drive outriggers went
fast compared to the submerged drive mono's. From about 17mph mono's to 26ish riggers on the same amount of power. I used exhaust throttles on the TD's for best power management. I am curious about the pipe length on your tunnel design did you fabricate the outboard or retro fit the engine to vintage unit?
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Old 05-12-2015, 12:55 AM
  #78  
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I made the outboard myself.
If I find the pipe, I'll measure it.
Funny thing I remember is, I ran incredibly high compression heads, like you would never get away with on a plane. But perhaps it was the water cooling, it ran sweetly like that, and the time a head plug failed and I used a stock cox head, it couldn't get planing the torque was so refuced.
it makes me wonder if the crank surviving the high rpms might have been from the extra high comp. ratio.

I had the same experience with the surface drive: night and day.
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Old 05-12-2015, 03:08 AM
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I could run higher rpm with surface drive the loads on the engine are less then with an air prop pulling a plane around. So the loads on the ball socket and piston rod made it possible. When I raised timing to 170 the combustion chamber was expanded so high compression head is a absolute must or the power loss is too great as you observed.
I plan to only run with one shim about 155 deg and do the cylinder mod is the best way to insure the pipe is boosting the cylinder. The Bolly Book stated tuned pipes will not function on anything less the 140 deg timing - if 2 shims gives me 170 odds are per shim its 15 deg.
http://www.bolly.com.au/book/Book.ph...er=6&Section=4

The engine was difficult to run at 170 deg the NV was way to sensitive with the Tarno Carb. I have a non SPI cylinder on 1 shim and so far it show promise. I am waiting for the single bypass cylinder to come in before I decide which cylinder gets filed. You had mentioned before you hadn't done any work to the porting, did you use a RC carb?

I plan to grind down some of the aluminum off the bottom of the glow head to seat it further down for higher compression to make up for the shim- I want to regain the same amount of compression prior to the shim.

With an outboard how did you manage to hang the pipe forward over the length of the boat?


Check this out I made a Micro Cracker boat with a TD .020 water cooled and exhaust throttle surface drive with a 20 mm surface prop

https://www.youtube.com/watch?v=gSqH9EZGKKc

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Old 05-12-2015, 03:35 AM
  #80  
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This looks promising perhaps a 1/2A version.



http://www.rbinnovations.com/category_s/3.htm


https://www.youtube.com/watch?v=b8KKbmMtuGg

https://www.youtube.com/watch?v=3bi5h7Tf2BY
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Old 05-12-2015, 10:38 AM
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Nice boat! I really wish I had video of the outboard boat running now.

I only used non spi cylinders, as at the time I thought it would be impossible to run a pipe with a spi cylinder- but Andy W was the first to prove norvels run on a pipe just fine, even though they have spi.

I didn't use base gaskets, for the reason you mention, instead I cut the exhaust ports higher. I thought at the time this would be important to increase blowdown time.

I have since run several 1/2A size motors on a pipe, and found that the idea of sub X port timing not working to be not true.
I suspect this comes down to the relative densities of air to the engine- as you get smaller, it goes up, so things change, like Reynolds numbers for airfoils.

yeah the pipe on an outboard was a bit of a headache! I made it in a curly S shape.
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Old 05-12-2015, 12:05 PM
  #82  
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With SPI you have to either tune to the SPI or tune for the boost going directly into combustion chamber cant do both. The window for SPI is smaller than the later but can confirm it does work with a cox engine there is a small loss using a piped system once tuned it is regained and I have had 22k plus static with a APC 4.5 x 4
The SPI function acts like a vacuum and could actually be doing good work for such a small gap.
I think opening up the top of the exhaust port allows more window time for the boost charge.


Ahh ok figured you had something rapped around the out board engine. I have been using a hat mounted video cam will have to
find some water and get my mono uploaded on YouTube will message you if you like to check it out.
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