Do Killer Bee back Plates sold onlne give better perf?

Are you looking for performance ?

Someone not long ago published directions on how to modify existing horseshoe backs to improve their HP production. I've found that the gray Sure Start backs are a bit touchy to try this. Trying to gently remove the spray bar in one caused the plastic to split, very brittle. The DuPont Delrin nylon ones are more durable.

I'd say if you want to try the KB one, go for it. There are a few other things to do to improve power, but the more free flowing KB back is a step in that direction.

Nice thing about the Coxes is one can do a number of things to improve performance without spending a bundle.

SkyStreak wrote:What makes the red KB one better.
I would like to buy a KB back plate and try it but I don't want to find its no different that what I have.
I have several of the beige back plates already.

I'm not sure if the one's you're looking at have a fine-thread needle-valve assembly.. but a backplate/carb having a fine-thread needle-valve assy. has the benefit of having a finer-resolution tuning for the engine. If you plan to experiment with a pressurized fuel-feed (bladder); then the fine-thread NVA is a must-have.

Your engine should be built to make the best use of all the parts being used.. for what the engine will be used for.

More airflow is good.. but remember; the reed is awesome when it's working.. but a tiny piece of grit ingested and getting stuck under the seat will end the activity and require removing the back-end of the engine to clean the reed/seat area. That's why Cox's sport-engines have a mesh metal screen in the air-intake.

Hi SkyStreak,
  Check here, https://www.coxengineforum.com/t6170-modifiying-horseshoe-backplates
If you're interested, I'll whip one up for you, under under one condition, you use it and keep us posted
on your progress. I'm not kiddin'. I was educated by St. Joseph nuns.
PM me your address, and I'll get t out by Monday. Totally gratis of course
I'm sure our brothers here can turn her into a monster.
Bob

The above is all good info for .049" and .051" cubic inch engines, but make sure you get the type that fits both your airframe's engine mounting area, and fits the application you want in performance. Fine thread needle valves will need to be found and scavenged from older engines, and we will help you with any boring of the venturi. As someone stated .084" is as wide as you want to go with suction fuel feed on an integral(built-in Bee type) tank style engine, and the bigger it is, the less user friendly it will be, as well as lower flight time due to it being thirsty. For a pressurized fuel system with a front rotary intake valve(like on a Tee Dee or Medallion .049), up to .150" wide is about as good as it gets before it becomes too finicky, and less power benefit.
Rusty

I found in some of my parts a back plate with no screen and it got me thinking that it was similar to a KB back plate.
I have an engine I've been experimenting with that so far I'm getting 17,000 with 15% and a 5x4 prop. Now that I discover this back plate I need to try it to see if it has any improvement on perf.

Drilling the backplate to 11/64" or a #16 bit is about as large as you can take the hole size up too. Anything larger equates to problematic fuel draw. There's nothing very specific about the Killer Bee backplate that sets itself apart from the rest. It's been said the early versions came with a fine needle valve assembly but I've never seen one. In reality, if you want more performance, up the nitro.

I have a few that I mounted on my active reedies and see a tad of performace improvement over the conventional horseshoe backplates. Probably the free flying reed under the reed retainer flanged cup with longer reed clearance than the beryllium allows easier and more  generous fuel-air mixture charge into the crankcase?

This is the backplate that I bought.. (less fuel-line and needle) coarse-threaded NV-body BTW..



The air-intake is unobstructed.. (no mesh-screen) and looks (to me) to have a smooth-dished orifice; as compared to a "sport" horseshoe-type backplate that has a screen. You could look at it as a sort of "tunnel-ram" reducing turbulence in the venturi.

SkyStreak wrote:I found in some of my parts a back plate with no sceen and it got me thnking that it was similar to a KB back plate.
I have an engine I've been experimenting with that so far I'm getting 17,000 with 15% and a 5x4 prop. Now that I discover this back plate I need to try it to see if it has any imrovement on perf.

17K is a good number for that prop and fuel, 25 or 30 nitro will give a boost for sure. Getting over 18K usually takes some work.  The new old stock red backplates are brittle, I have cracked two. Don't honk down on the screws too much, they crack at the venturi. Another tip was to turn the fuel outlet in the spraybar a few degrees away from directly downstream of airflow in either direction, I think that one came from Larry the Renger himself. This is one of Matts EX engines, it has a Surestart cylinder and shortened, lightened piston to allow SPI. Cant see tach but turned 19K with standard head. High comp head and some tuning probably could get over 20K easy.


It really sucks fuel

High static rpm with a mylar reed / Killer Bee backplate & crankcase
but not the piston and cylinder.



Best peak 24,790 / 7.1oz thrust / 106 mph pitch speed / 93.3w
Nelson plug / 25% nitro / HQ Carbon 4x4.5 prop


intake variable per throttle barrel
mylar reed



Best peak noted at 23,336 rpm
APC 4.1x4.1 / peak rpm hit 91 mph pitch speed


 

WOW!! nut= speed demon!! Cool, glad you never sent any engines to the old tach races.

Thank you,
I do plan to build a test plane for Cox reed engines .049 - .051
Will be fun to discover what is possible with RC Reed Speed.
They have a unique sound compared to TD engines.

Almost sounds like a threat to start an online RPM contest with a standard unmodified propeller/fuel mix. Maybe the APC 4 1/4 - 4 prop or something similar that is readily available still. Reedy and rotary class. Bragging rights, no cash is best. I can not say much about the KBee backplates, but imagine the carb bore is just slightly larger than the others. I only have one separate white backplate and pulled the needle assembly to file the bore a bit bigger. That would be the older G clip copper reed. Maybe the mylar reed with the newer retainer is faster. IDK.

Lol Alan true,

The RC carb by eyeball looks like a reasonable intake dia. of course it was made to feed the thirsty TD engine.
Does not seem to be a issue with the reed valve. APC 4.1x4.1E is plenty stout to handle the engine, the thinner
blades let the reed engine gain some fresh new useable performance compared to the fat bladed IC props.

i have tried some crazy stuff with KB backplate, this one failed. It did run 19.5K on 25% and a 5/3 gray cox prop. Standard head.
Too much vibration in the intake.

crankbndr wrote:

SkyStreak wrote:I found in some of my parts a back plate with no sceen and it got me thnking that it was similar to a KB back plate.
I have an engine I've been experimenting with that so far I'm getting 17,000 with 15% and a 5x4 prop. Now that I discover this back plate I need to try it to see if it has any imrovement on perf.

17K is a good number for that prop and fuel, 25 or 30 nitro will give a boost for sure. Getting over 18K usually takes some work.  The new old stock red backplates are brittle, I have cracked two. Don't honk down on the screws too much, they crack at the venturi. Another tip was to turn the fuel outlet in the spraybar a few degrees away from directly downstream of airflow in either direction, I think that one came from Larry the Renger himself. This is one of Matts EX engines, it has a Surestart cylinder and shortened, lightened piston to allow SPI. Cant see tach but turned 19K with standard head. High comp head and some tuning probably could get over 20K easy.


It really sucks fuel

crankbndr: where did you get the syringe? I like the idea. Small fuel supply, and calibrated.

if only i had time to run some engines. i am still on garage cleaning duty. i recently put some old 128tpi needle valve assemblies into some new KB backplates. haven't had a chance to put one onto an engine assembly yet.

happydad.

Hay Happy, unfortunately I have have been around a lot of nurses and hospitals. Those syringes are full of saline so I either ask for a few or steal some or both.

aspeed wrote:Almost sounds like a threat to start an online RPM contest with a standard unmodified propeller/fuel mix.  Maybe the APC 4 1/4 - 4 prop or something similar that is readily available still. Reedy and rotary class.  Bragging rights, no cash is best.  IDK.

I think this would be a great idea. Keep it simple though limit it to parts that are Cox production parts.

SkyStreak wrote:

aspeed wrote:Almost sounds like a threat to start an online RPM contest with a standard unmodified propeller/fuel mix.  Maybe the APC 4 1/4 - 4 prop or something similar that is readily available still. Reedy and rotary class.  Bragging rights, no cash is best.  IDK.

I think this would be a great idea. Keep it simple though limit it to parts that are Cox production parts.

Best to check the archives for the old Tach Race threads. We've done it all before. The whole thing was a huge drain on the host and interest has all but died out. Looks like the interest might be returning. Back then, because the runs were controlled by one person then it was all fair and above board, hence it had significant prizes. (I won a NIB Black Widow for my Mouse entry. By the way, I think I'm still unbeaten. 24,100 rpm on a tanked reedy )
There was some talk about a "proxy" tach race, which is maybe what you guys are talking about. The idea would unfortunately be open to corruption, plus a lot of variation in fuels, props climate etc.

Oldenginerod wrote:

SkyStreak wrote:

aspeed wrote:Almost sounds like a threat to start an online RPM contest with a standard unmodified propeller/fuel mix.  Maybe the APC 4 1/4 - 4 prop or something similar that is readily available still. Reedy and rotary class.  Bragging rights, no cash is best.  IDK.

I think this would be a great idea. Keep it simple though limit it to parts that are Cox production parts.

Best to check the archives for the old Tach Race threads.  We've done it all before.  The whole thing was a huge drain on the host and interest has all but died out.  Looks like the interest might be returning.  Back then, because the runs were controlled by one person then it was all fair and above board, hence it had significant prizes.  (I won a NIB Black Widow for my Mouse entry.  By the way, I think I'm still unbeaten.  24,100 rpm on a tanked reedy )
There was some talk about a "proxy" tach race, which is maybe what you guys are talking about.  The idea would unfortunately be open to corruption, plus a lot of variation in fuels, props climate etc.

If there are no prizes, then you are only cheating yourself. Maybe a picture of the the tach. I am sure someone would be cutting the prop down. Nitro content could be an issue if not available. I can rarely get 15%, unless I mix it.

Hi Rod,

What prop did you use to get 24.1k rpm with a tanked reedy mouse entry and % nitro used?

They say not to go over .082 ventury on a tanked engine. How do you calculate the intake size on a horseshoe bake plate. The spray bar divides the intake.