black widow performance question

5.5x3 is a "bigger" prop, so I would expect lower numbers than with a 5x3 cox contest prop.

Yes, lots of variables.

Phil

Sorry about the quick question, let me tell you whats happening. I have two home made black widow's. They were built with widow tank kits from cox before they closed. The rest of the parts were just the best stuff I could find at the time, and i'm think of making some changes. They have not been run in a few years and not since I got a tach. So I never new what they would turn, only that they were faster than babe's and ran longer. For some reason I expected them to run much faster than it did, but by what you guy's say its doing ok. The first engine settled down after four runs and needled well. It made a solid 16800, and flashed up over 17000 once, but a honest 16800 anyway. The engine has a slit exhaust cylinder with two transfers and one boost per transfer, no SPI. It has a merlin drop in with four shims. I am thinking about changing the cylinder.
I'm going to have to tear down the second engine. I cant get a good solid run on it, so it's coming apart for a good cleaning.
Phil

Before you do anything, take the engine to a good light and hold it up to it so the light shines through the exhaust. Rotate the engine to Top Dead Center and look for light shining below the skirt of the piston. If there is a slight glint then there probably is not enough to pretend it is Sub-Piston Induction (SPI) If there is good light showing then you may want to measure it or estimate the SPI. I suspect you have some.

Next get a 5/64 or 2mm drill bit. See if the passage through the tank is opened to this size already. If not disassemble and open it up. This can be done to Baby Bees to hop them up quite nicely!

The slit exhaust vs the open port is a non-issue unless you need that very last iota of power.

Phil

I think you're in the ball park with 20% nitro, try removing a gasket and see what that does, if so, try two? As you probably know there's a lot of variables to a strong running engine, piston fit (little loose) new reed, proper compression, etc. Also, check the inside diameter of the air tube on tank, they were made in two different sizes, if your running a "black" golden bee tank or one of the later versions it might be the smaller diameter and opening up the backplate won't really help much.
If RPM is jumping all over, replace reed and clean needle, slip fuel line over to seal, check glowhead gaskets.

pkrankow wrote:Before you do anything, take the engine to a good light and hold it up to it so the light shines through the exhaust.  Rotate the engine to Top Dead Center and look for light shining below the skirt of the piston.  If there is a slight glint then there probably is not enough to pretend it is Sub-Piston Induction (SPI)  If there is good light showing then you may want to measure it or estimate the SPI.  I suspect you have some.
Next get a 5/64 or 2mm drill bit.  See if the passage through the tank is opened to this size already.  If not disassemble and open it up.  This can be done to Baby Bees to hop them up quite nicely!
The slit exhaust vs the open port is a non-issue unless you need that very last iota of power.
Phil

Mark Boesen Today at 1:06 am
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I think you're in the ball park with 20% nitro, try removing a gasket and see what that does, if so, try two? As you probably know there's a lot of variables to a strong running engine, piston fit (little loose) new reed, proper compression, etc. Also, check the inside diameter of the air tube on tank, they were made in two different sizes, if your running a "black" golden bee tank or one of the later versions it might be the smaller diameter and opening up the backplate won't really help much.
If RPM is jumping all over, replace reed and clean needle, slip fuel line over to seal, check glowhead gaskets.

So to modify a bee for more power you must open the tank venturi AND backplate air hole with the 5/64" drill, is that correct?  I believe the BW was .082".

I bought a tach and can't wait to get measuring and comparing props, reeds, venturi size, etc.

I'm buying Cox Super Fuel 25% nitro from my local Hobby Town store. They order it from SIG or Tower I think, but I pay no shipping.  Since it sounds like you experienced modelers prefer higher RPM and speed why would one want to run 15% or 20%?  The stuff I have is 10% castor and 10% synthetic.

Greg

The back plate hole should already be larger than the 5/64 drill. I am nearly positive of this. Even the old screened metal plates if you knock the screen out. I don't know the actual size of the hole in the back plate. There is no need to modify the back plate.

The passage through the fuel tank needs modified on the baby bee tank, and some bee tanks (many are already the larger size). It is possible to go larger than 5/64, but only a couple thousandths. If you go too large then the engine will become very difficult to start and operate.

Phil

"So to modify a bee for more power you must open the tank venturi AND backplate air hole with the 5/64" drill, is that correct? I believe the BW was .082".

I bought a tach and can't wait to get measuring and comparing props, reeds, venturi size, etc.

I'm buying Cox Super Fuel 25% nitro from my local Hobby Town store. They order it from SIG or Tower I think, but I pay no shipping. Since it sounds like you experienced modelers prefer higher RPM and speed why would one want to run 15% or 20%? The stuff I have is 10% castor and 10% synthetic.

Greg"


Hi Greg,

Yes, to open the backplate and have a smaller diameter tube doesn't help much (off the top of my head i don't remember the inside diameter) just make sure its the larger of the two and remember this is for dual port cylinders only.
I've never drilled out the larger dia. or messed with shorting/lightening pistons, but I do a lot of piston lapping, swapping, ball resetting, and head gasket changes. Personally i'd take a loose, well fitted piston (snug ball) over an increased SPI piston anyday.

Here's the best artical on the 'net to get the most out of your engines:

https://www.coxengineforum.com/t753-the-revised-2011-gibeault-mouse-race-program

Mark Boesen wrote:"So to modify a bee for more power you must open the tank venturi AND backplate air hole with the 5/64" drill, is that correct?  I believe the BW was .082".

I bought a tach and can't wait to get measuring and comparing props, reeds, venturi size, etc.

I'm buying Cox Super Fuel 25% nitro from my local Hobby Town store. They order it from SIG or Tower I think, but I pay no shipping.  Since it sounds like you experienced modelers prefer higher RPM and speed why would one want to run 15% or 20%?  The stuff I have is 10% castor and 10% synthetic.

Greg"


Hi Greg,

Yes, to open the backplate and have a smaller diameter tube doesn't help much (off the top of my head i don't remember the inside diameter) just make sure its the larger of the two and remember this is for dual port cylinders only.
I've never drilled out the larger dia. or messed with shorting/lightening pistons, but I do a lot of piston lapping, swapping, ball resetting, and head gasket changes. Personally i'd take a loose, well fitted piston (snug ball) over an increased SPI piston anyday.

Here's the best artical on the 'net to get the most out of your engines:

https://www.coxengineforum.com/t753-the-revised-2011-gibeault-mouse-race-program

Great invaluable info and wisdom in the pdf at the link above.
Here's the direct link:
https://dbabd7f0-a-62cb3a1a-s-sites.googlegroups.com/site/nitroengine/TheRevised2011GibeaultMouseRaceProgramv3.pdf

Greg

I tore down my second engine for cleaning, gaskets, reed, fuel hose. The problem with it was a very thick deposit on top of the piston. The compression was to high. Anyway, during re-assembly one of the tank screws went through the plastic back plate before it was even snug. I got so disgusted I put it in a bag and tossed it in the parts bag. I cant deal with that right now. 11.95 plus shipping to fix 1.00 worth of plastic.

Caution, mild rant about the crap plastic back plates

I got sick and tired of fussing with the plastic back plates and spent a year amassing a fair supply of the metal back plates by bidding and occasionally winning groups of dirty, nasty, mostly disassembled .049 cox engines...several "lots" had 4 or 5 metal back plates, some with a broken ear

My opinion is a metal back plate with three ears is better than a plastic BP any day... However, I managed to get one good 4 eared metal back plate for each of my 19 Bee type .049s for not all that much scratch

I know Bernie has always said the cost to get a mold done, and minimum parts order from his supplier is cost prohibitive and he makes sense--- but I think if I had a choice I would buy several metal back plates over the plastic lesser expensive part

That said, the reverse is true for me with the carb body of a TeeDee....I find the plastic reproduction and cost to be better than the very nice machined metal part....I crash a LOT with my TeeDee powered combat trainers and never screwed up the new plastic carb body...old brittle ones yes ....other than being very good looking, the 2 metal carb bodies I bought were not money well spent