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Post  fit90 on Sat Jan 21, 2012 6:14 pm

starting a pressurized Cox Start press cox
Hope this works
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Post  fit90 on Sat Jan 21, 2012 6:15 pm

Nope, computer is smarter than I am
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Post  nitroairplane on Sat Jan 21, 2012 6:17 pm

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Post  fit90 on Sat Jan 21, 2012 7:38 pm



I hope this works this time

Sorry, not yet
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Post  microflitedude on Sat Jan 21, 2012 7:42 pm

"The video you requested is not available"

Are you sure you don't have the video listed as private only?
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Post  fit90 on Sat Jan 21, 2012 7:45 pm

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Post  fit90 on Sat Jan 21, 2012 7:46 pm

This is a lot of work!!! If anyone thinks it's not hard being dumb they are wrong! Just ask me.
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Post  microflitedude on Sat Jan 21, 2012 7:47 pm

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Post  dckrsn on Sat Jan 21, 2012 8:16 pm

fit90 wrote:This is a lot of work!!! If anyone thinks it's not hard being dumb they are wrong! Just ask me.

Hey, you didn't know, you found out how, and you did it.

Nothing dumb there.Wink

Bob
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Post  RknRusty on Sat Jan 21, 2012 9:44 pm

Hey, Bob, I posted a comment on your video. That's a fast freakin' little Surestart "Type" engine. I almost ducked under my keyboard! What's that thing tach out at?

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Post  fit90 on Sat Jan 21, 2012 9:56 pm

It's turning just a little over 19K in the video, probably around 19.2 to 19.3. I am hoping to get this one to top 20K. I am using straight Sig Champion 25% and a Cox 5X3 stiff grey prop. I drilled out the venturi with a #10 bit, used a 128 tpi NVA from a 290 engine and opened up the spray bar hole a few thousandths and put it on an engine with a polished KB crank, SPI piston/cylinder and Galbreath head and Nelson plug with one gasket.
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Post  dckrsn on Sat Jan 21, 2012 10:15 pm

fit90 wrote:It's turning just a little over 19K in the video, probably around 19.2 to 19.3. I am hoping to get this one to top 20K. I am using straight Sig Champion 25% and a Cox 5X3 stiff grey prop. I drilled out the venturi with a #10 bit, used a 128 tpi NVA from a 290 engine and opened up the spray bar hole a few thousandths and put it on an engine with a polished KB crank, SPI piston/cylinder and Galbreath head and Nelson plug with one gasket.

IT'S ALIVE! Nice work.

Bob


Last edited by dckrsn on Sat Jan 21, 2012 10:23 pm; edited 1 time in total
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Post  RknRusty on Sat Jan 21, 2012 10:16 pm

fit90 wrote:It's turning just a little over 19K in the video, probably around 19.2 to 19.3. I am hoping to get this one to top 20K. I am using straight Sig Champion 25% and a Cox 5X3 stiff grey prop. I drilled out the venturi with a #10 bit, used a 128 tpi NVA from a 290 engine and opened up the spray bar hole a few thousandths and put it on an engine with a polished KB crank, SPI piston/cylinder and Galbreath head and Nelson plug with one gasket.
What angle do you position the spraybar orifice, stock straight ahead, or do you aim it off-center?

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Post  nitroairplane on Sun Jan 22, 2012 4:47 am

Yeah that is one hot engine man!
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Post  PV Pilot on Sun Jan 22, 2012 5:51 am

Angry little cox motor,,nice work on the vid and engine.
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Post  fit90 on Sun Jan 22, 2012 7:41 am

The hole in the spray bar is facing directly into the back of the engine.
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Post  Mudhen on Sun Jan 22, 2012 8:58 am

fit90 wrote:The hole in the spray bar is facing directly into the back of the engine.
You may get a higher, steadier rpm, better fuel draw, more thorough atomization, and easier starting by canting the spray bar hole. The least amount of pressure in the venturi tube (thus the greatest draw,) will be that area between the inner diameter of the venturi wall and the outer diameter of the brass needle valve insert. My engine for tach race had the hole angled at 60 degrees. I'm not implying this is ideal. For this engine, it worked. For a pressurized engine, your mileage may vary. But it is worth experimenting with various angles.
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Post  fit90 on Sun Jan 22, 2012 9:59 am

Thanks for the input on the spray bar angle Mudhen. I remember reading something about that a while ago but could not find the info. I also learned that making the venturi and spray bar hole larger are only effective up to a cetain point. This NVA flows so much fuel under pressure that the needle setting is ultra sensative. I think I will redo the backplate and try the angled spray bar.

Thanks again,

Bob
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Post  andrew on Sun Jan 22, 2012 10:32 am

fit90 wrote:This is a lot of work!!! If anyone thinks it's not hard being dumb they are wrong! Just ask me.
Bob
That certainly explains why I'm worn out at the end of the day!! Spent the whole day working at being dumb and was too dumb to figure it out!!! Sad

Mudhen wrote:
......... more thorough atomization........... For a pressurized engine, your mileage may vary. But it is worth experimenting with various angles..........
Mud
You've brought up a valid point.
Certainly for a normally aspirated engine, the old Bernoulli velocity/pressure principle dictates positioning to minimize pressure at the spraybar hole for maximum fuel draw. OTOH, pressurized engines don't need a vacuum to draw fuel, but good fuel atomization is important. Burn surface plays a big part in everything from gunpowder to solid rocket motors, so better atomization means more burn surface, which should transfer to a better flame propagation rate, i.e., more rpm. Dumping fuel into a high velocity air stream would, I think, help atomization. For a pressurized engine, I wonder what effect having the spraybar pointed directly into the airflow would have? Either way, various spraybar angles can't help but be a player in squeezing the last 100 rpm out of the motor.
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Post  PV Pilot on Sun Jan 22, 2012 10:42 am

For years and years, the general consensus(still) around the drag racing community was that the more you can atomize Nitromethane, the more power you can get out of it. They have perfected the top end or second system nozzle orifice sizes to the point of shooting a fog type mixture into there motors. They have even gone(years ago) to adding a high speed pinch valve,,for a quick leanout,,to get that extra burst of power.

I was thinking of a couple extra pinholes around that spray bar, to break up those droplets even more.

Just some food for thought, and fun.
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Post  fit90 on Sun Jan 22, 2012 11:10 am

All this has me thinking to the point that I just ordered some more NVA's from Texas Timers. Unfortunately, I will be busy the next few weekends. But, when I get some more time to play with this I should have everything I need right at hand.
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Post  RknRusty on Sun Jan 22, 2012 5:50 pm

Glad I asked about the spraybar because I'm planning to build two Killer Bees as close to identical as possible for the Com Bats I got for Christmas. I'd like to try different positions if it can be fiddled with without loosening the spraybar too much.

Once I got a new red KB backplate with a loose spraybar that turned with the needle. I cleaned it of all fuel and JB Welded it but it came loose again. Maybe it can be re-positioned and then heated and the plastic will cool and grip it.

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Post  fit90 on Mon Apr 30, 2012 8:40 pm

Back up again
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Post  RknRusty on Mon Apr 30, 2012 10:23 pm

fit90 wrote:Back up again
Come again?

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Post  fit90 on Tue May 01, 2012 7:25 am

RknRusty wrote:
fit90 wrote:Back up again
Come again?

Instead of putting a link to this thread in the "Medallinon .15 side nipple" thread I was just lazy and bumped this thread back up.
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