Update: RCM Article For Cox Engine Backplate Modification

NEW222 Fri Mar 30, 2018 2:02 pm

Hi there. So while doing some reading this lazy Good Friday, I was thinking back to the early to mid 90's. I have remembered a tip in one of the Model Airplane News articles in the 'Hints & Kinks' referencing drilling /enlarging the intake on a Cox engine. Would anyone happen to remember or have this saved anywhere on their computer, or know where I can search it? To be more than honest, I would feel comfortable as memory serves, to say between 1992 - 1996. Just trying to see if I can get a copy as I may want to try it.... Thank you.

NEW222 Fri Mar 30, 2018 2:42 pm

Ok. Thinking it may not have been Model Airplane News now. I found a site that has them all and went through them and did not find the article I wanted. Now to go look for RCM Magazine....

fit90 Fri Mar 30, 2018 5:00 pm

I think there is a post about it on RCU's 1/2 spot. I have several Tee Dees will drilled venturis that are run on crankcase pressure. I also built a Sure Start will a drilled out intake than ran on crankcase pressure. I can take some measurements if you would like.

NEW222 Fri Mar 30, 2018 5:31 pm

I will try searching RCU and see if it comes up. Also, thank you for your offer, but you do not have to go out of your way. It was just something I was trying to find. This article in question was for a Bee type engine.

fit90 Fri Mar 30, 2018 6:33 pm

The offer still stands. ask any time.

Ken Cook Fri Mar 30, 2018 6:45 pm

A Black Widow can handle opening the intake to .093". However, this isn't always without issue. Hard starting, fuel draw issues, and shorter run times, and difficulty getting a decent flying setting becomes a factor. .082" would be a better option because the power gain isn't as substantial as most claims. A product backplate can be successfully opened to 11/64". While the engine will run with a slightly larger opening, a too large venturi shows it's ugliness on launch when the engine just quits upon release like someone turned off a switch. This is where the need for pressure is required.

NEW222 Fri Mar 30, 2018 7:18 pm

fit90 wrote:The offer still stands. ask any time.

Thank you.

NEW222 Fri Mar 30, 2018 7:20 pm

Ken Cook wrote: A Black Widow can handle opening the intake to .093". However, this isn't always without issue. Hard starting, fuel draw issues, and shorter run times, and difficulty getting a decent flying setting becomes a factor. .082" would be a better option because the power gain isn't as substantial as most claims. A product backplate can be successfully opened to 11/64". While the engine will run with a slightly larger opening, a too large venturi shows it's ugliness on launch when the engine just quits upon release like someone turned off a switch. This is where the need for pressure is required.

Hmmm. Kind of funny, but after reading your post, it almost sounds like you quoted the article in question. The numbers in decimal almost sound familiar as does your talking of fuel draw and starting issues, as I believe that that was also covered in the 'hint' I am looking for. Thank you.

fit90 Fri Mar 30, 2018 7:41 pm

Both Paul Gibeault and Rusty have had some excellent posts about mouse engines which probably cover all this information.

My little bit of experience with opening the venture on a reedie was to open it using an 11/64" bit, install a fine NVA and to use crank case pressure to eliminate fuel feed issues.

This shows where the pressure tap goes through the crank case:

Update: RCM Article For Cox Engine Backplate Modification Ss111

This shows the opened venture:

Update: RCM Article For Cox Engine Backplate Modification Ss211

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This shows the pressure tap exiting the crank case supported by a blob of J B Weld. The inside of the pressure tap was filled with solder and then a hole was drilled through the solder with a #80 bit

Update: RCM Article For Cox Engine Backplate Modification Ss411

Oldenginerod Fri Mar 30, 2018 7:58 pm

Here's a link to Paul Gibeault's Mouse Racing article. It describes the modifications you refer to.

Rod.

https://coxengines.ca/files/MRP.pdf

NEW222 Fri Mar 30, 2018 8:27 pm

Oldenginerod wrote:Here's a link to Paul Gibeault's Mouse Racing article. It describes the modifications you refer to.

Rod.

https://coxengines.ca/files/MRP.pdf

Thank you. This is actually funny, as I was reading this article earlier looking for a part about sanding the tank back flat for another individual here asking about it. After quickly glancing through the article a few times, I did not see what I was looking for. But, now that you linked it to me on my question, the part I was looking for earlier is in the same paragraph!

pkrankow Fri Mar 30, 2018 8:49 pm

I opened my baby bee tank venturi to 5/64, which is a couple thou off 2mm and it is a nice easy hop up that does not detract from operation... well, they run out of fuel quicker. Same starting, same running, more power. Does not work so well with an old single bypass cylinder (little to no performance change), but on the newer double bypass, and double bypass with boost it offers a few hundred rpm with little risk to the engine.

Phil

Tee Bee Fri Mar 30, 2018 8:51 pm

I'm not sure how far the Venom II venturis that Bernie is selling currently are drilled out, but mine so far has started easily, launched great, and makes significantly more power than the Black Widows I've tried on the same airplane(Sharkface). Running it stock with no pressure taps or other mods. It has had me thinking about drilling out one of the BW venturis to compare notes. The only drawback I've noticed with the hotter engine is a shorter runtime, about 1.5 minute.

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Update: RCM Article For Cox Engine Backplate Modification

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