fit90

Does anyone have any suggestions on how far a Tee Dee .049/.051 venturi can be drilled out? The engine I want to try this on uses a lightened piston, Galbreath head/Nelson plug, Backplate pressure and a fine thread NVA. I typically run Sig Champion 25% with added castor and turn a cut down APC 5.7-3 cut down to about 4.9-5.0. I think the engine has some unused potential that just requires a little extra fuel to take advantage of. I know that I have seen some suggestions on this forum but I can not find them. I am still looking though.

Thank you,

Bob

combatpigg

My Feedback: (3)

A TD that is propped for more rpm than what you will get from a 5.7x3 can make good use of a 5/32" venturi. I would try 1/8" first and see what you get with your combo, then go to 5/32" if you get curious.

Jim Thomerson

Back in the mouse racing days, I drilled them out to 1/8 inch, and used back plate pressure with a shutoff pinching both fuel and pressure line.

Lifer

My Feedback: (1)

Jim,

Did you ever race "Mouse" at the Nats?

Toad

I used a 5/32 bore on mine (.156) on the same setup. I also went with .008 spi or LESS. worked good for me and .156 is what Cox suggests in the instruction sheet. be sure to clean out the fuel jet holes after reworking the bore, they tend to burr over some.
1/2a pylon

hllywdb

I use 5/32 on backplate pressure. I have also used the spacers under it. Hey, TD Tunnel Ram!

fit90

Thanks for all the help.  I think I will start with the 1/8" venturi and if all goes well I will try the 5/32" opening.  I think that I am finally ready to start experimenting with props smaller than five inches.  I think if my plane is 10 ounces or lighter and not too draggy it will work out well.  If not it will still be fun finding out.

I used to fly 1/2 A a lot in the mid 80's with mixed results.  After shamelessly stealing some ideas and tips from you guys I am finally getting some good performance along with dependability.  These little engines are proving to be a lot of fun.

Thanks again.

Bob

fit90

HOLY CRAPOLI!

I just drilled the venturi out with a #22 bit which I measured out to .155" with an out of certification vernier caliper and put an APC 4.5-3.5 on this Cox Tee Dee .051 as described earlier except that this one has a standard Tee Dee .051 piston and got 25K right off the bat.  Also, I enlarged the fuel jet holes by a few thousandths each when cleaning them.  I do not know what size bit it was but I would guess between a #80-#85.  The engine ran consistently through an ounce of fuel. No burbling, belching, going lean or rich. Super performance and dependability for me.  I have to look for this in my next girl friend.  After I finish my current projects I think I will build a Cam Racer for this bad boy.  In the mean time I will keep experimenting with props and with lightened pistons.

Thanks again for all the help!

Bob

Larry Driskill

'Tis good that you are having success with your venturi modifications.

Girl friends could be more complicated . . . .

Just as an aside: A Fox standard 1/4X32 long plug can be modified to serve as a TeeDee .049 venturi.

The "post" has to be knocked out and the resulting hole drilled out to an 1/8" , or so.

The threads are the proper size and there is a relief above the plug thread in just the right place for the fuel from the needle body to flow around the plug/venturi.

You just have to drill some small fuel feed, jet holes in the relieved area.

mikegordon10

I never had a hard time getting TD's to turn up. But getting them to hold together was another problem.

fit90

Larry,

I totally agree-girl friends plus wives and ex-wives are all very complicated, at least for me.  I will try the fox plug/venturi mod some time soon.  Thanks for letting me know about it.  Also, thank you for all the parts support.  At minimum, the Galbreath heads and Nelson plugs that I use are from you.  I have also used some of your fine thread needle valves in experiments with some of my Norvels.  Thank you for supporting those of us that still play with these fun little engines.

Bob

gcb

Keep a close watch on that ball-socket!

George

fit90

I just took a Tee Dee .049 I plan on using on a DNU and put it together with the Galbreath head, Nelson plug, lightened piston, pressure tapped backplate, fine thread NVA and .155" venturi.  With three head gaskets (I don't know their thickness) and on Sig Champion 25% with added castor it turned an APC 6-2 at 21k through on ounce of fuel with great dependability and consistency.

Thanks again for the help on venturi size and everything else,

Bob

hllywdb

Try 2 head gaskets and a 5.5 X 2, with the larger venturi you need to let it unload. I agree with George, buy the piston reset tool. After run in you will need to tighten it up and then check it when the rpms start to lag.

fit90

I think I will try the 5.5-2.5 after some test flying.  As much as the engine likes to keep its RPM up I wan to keep the speed down.  The additional thrust of the 6 inch prop is an added bonus.

Resetting the piston to conrod ball is paramount to longevity on all Cox engines.  I typically reset mine every 10-15 flights, when ever I have the engine disassembled or at the first sign of abnormal starting or running.  I think this might be a little over kill but  I use a full size electric starter and will occasionally try to drill my planes into the ground.  The only part I have ever had fail on a Tee Dee has been a modified crankshaft.  I thoroughly believe that I am luckier than I am good with these engines but I will gladly take what I can get.

By the way, the 5.5-2.5 on an .051 Tee Dee with the stock venturi flew my 16 ounce Hummer around fairly well.  A little slow but still acceptably well.

Thanks for the tip,

Bob

VGE Hobbies

My Feedback: (9)

Bob,

That was one of my custom pistons I milled out for you right?

Reggie

fit90

Reggie,

No, these are some.049 cylinder/pistons I had from other engines.  I got your .051 cylinder/pistons Wednesday and if I am lucky I should be able to give them a few runs this weekend.  Both the pistons and your work are super beautiful.  However, because of the taper fit I think they will require some breaking in to achieve their best performance.  I have really high expectations for them based on your work and the really tight taper fit they have.  I will try to reach you Friday or early next week to talk about the crankshafts.

Thanks,

Bob