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Cox Engine of The Month
August-2019
fredvon4's

"Tee Dee .049"



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Post  geoffwise on Mon Jun 10, 2019 7:56 am

dens model supplies
Dual bypass ports
Sub-induction (SPI)
Dual booster ports (one per side)
(The same porting as TD #4 Cylinders )
Brand new Current Production item

These are special manufacture; whereas we took a #1 Production cylinder, removed the bar in the exhaust ports and lowered the bottom port cut-out to induce SPI. (cannot be used with a muffler)!!!!!!!!!!!!!!!!!!
his item is derived from disassembling brand new, never-run, engines and may show minor traces of having been mounted and/or minor tool marks.

Features:cox int
Dual bypass ports
Sub-induction (SPI)
Dual booster ports (one per side)
(The same porting as TD #4 Cylinders )
Brand new Current Production item

These are special manufacture; whereas we took a "Production" cylinder, removed the bar in the exhaust ports and lowered the bottom port cut-out to induce SPI.

This cylinder will equal OEM Tee Dee cylinder performance and is currently our highest-performance cylinder but please note that they are not "tapered" and the piston can be slid through the top of the cylinder.

Inside of exhaust ports will be unplated (not oxided).

Application:
All Cox .049 Tee Dee engines
All Cox .049 Medallion engines
All C


You can Not use am muffler with SPI but do not all tds have spi??? And this one?? /#11-Cox .05 Tee Dee RC Engine . .So you ask what is this about I have 049 050 051 TDS and 2 off the new crap one's re built so they work and a tarno 1/2a To SPI or not to SPI that is the Answer Geoff
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Post  KariFS on Mon Jun 10, 2019 11:33 am

I am pretty sure that both cylinders come from the same source.

Most people think that SPI and muffler is not a good combination. I don’t have enough practical experience to say for sure, but I did receive a couple of Tee Dees with mufflers installed, and the guy had run them a lot and did not mention any problems. The engines were covered in castor so they had obviously been run a lot in that configuration. And Cox did market mufflers for Tee Dees as an accessory. So they do work, but the muffler probably affects the performance.

The Tee Dee .05 R/C has a special non-SPI cylinder. The bore is the same as in .051, by-passes are like the ones on regular Tee Dee, only difference is the lack of the SPI.

As far as I know, all Cox engines that came with a muffler as standard (Tee Dee R/C .05 and .09, Medallion R/C, R/C Bee, Dragonfly, QZ, QRC and Queen Bee), were without SPI.

I ran some side-by side tests with a couple of Babe Bees, both had the late style double-slit cylinders, and during that test I did not see a significant difference in rpm whether the muffler was installed or not. A Tee Dee head did not change things much either, except the needle adjustment got a bit ”fiddly” with the high comp head. So the conclusion of that test was that with a non-SPI cylinder the muffler does not rob performance. Your results may vary Smile
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Post  geoffwise on Mon Jun 10, 2019 1:24 pm

Thanks KariFS, that is what I expected with no spi. So using a td with same top end should be the same. I will have tested it. Non spi first but home running is not on! With no muffler! With a non spi top end it should be the same as a MEDALLION or better and then the rc carb with pressure.
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Post  ffkiwi on Mon Jun 10, 2019 5:38 pm

geoffwise wrote:Thanks KariFS, that is what I expected with no spi. So using a td with same top end should be the same. I will have tested it. Non spi first but home running is not on!  With no muffler! With a non spi top end it should be the same as a MEDALLION or better and then the rc carb with pressure.

Well a genuine Medallion cylinder only has one transfer-so even allowing for some losses -you should still be ahead of the game using a TD cylinder and muffler. Do not however underestimate how brutal the effects a muffler can have on power when fitted to an SPI engine-I provide the two links below as examples. The first is directly relevant as an 049 example, whilst the second shows an extreme case.... Note that I am not implying you would experience this degree of loss with a TD cylinder-merely that it provides well documented proof from an unimpeachable authority-PGF Chinn himself -of what CAN happen when mufflers are fitted to engines with SPI...

http://sceptreflight.com/Model%20Engine%20Tests/Davis-Charlton%20Quickstart%20Wasp.html

http://sceptreflight.com/Model%20Engine%20Tests/ST%20G.20-23.html

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Post  Oldenginerod on Mon Jun 10, 2019 6:53 pm

I recall seeing an old advertisement somewhere for a Tee Dee muffler kit which instructed the installer to use timing shims under the cylinder to get rid of the SPI. These shims are sold by Cox International for this purpose.

Also, I'm pretty certain that Den's Model Supplies is an agent for Cox International, so the Cox products they sell should be identical.
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Post  ffkiwi on Mon Jun 10, 2019 7:44 pm

I should amplify my comment above-a genuine STANDARD Medallion cylinder has only one transfer-some of the later R/C ones have two-but single flute, not with the additional bypass grooves on either side that the TD has. then later on you went from open exhaust to slit exhaust-which further complicates matters-in terms of variables. AFAIK nobody has the ability to remanufacture Cox cylinders in the way that Cox did it-to the original specs-and Cox International are doing their best to meet the needs of the customers by modifying existing inventory cylinders to meet the specs-as closely as can be done-of the original types.  Here is a typical example: https://coxengines.ca/cox-.049-tee-dee-cylinder-and-piston.html

I suspect this is largely because the original equipment used for manufacture has long since been superseded in general light engineering manufacture

So what you get is a 'best we can do now' version of the original using late OEM production cylinders as the starting point-so now there is a whole raft of 'retro' cylinder porting variations possible when compared with the originals....the net result being that some combinations if retrofitted will perform better than the original Cox OEM engine, others about the same-and others somewhat worse.

The original TD 049 used a tapered bore-the 'retro' cylinder does not-the original Killer Bee used both a tapered bore AND a lightened piston-thus accounting for the amazingly good-for a reed valve-performance. The differences may be subtle-but they stack up.  Essentially now we have a situation where-depending on the age of the engine-and what if any retro parts have been fitted-there is now an entire spectrum of performance possible-rather than the fairly clear division of power in steps that existed in the past  ie. Babe Bee - Golden Bee- QZ- Black Widow -Medallion TeeDee -KillerBee.....throw the various product engines plus the Texaco, the R/C Bee/Dragonfly into the mix-allow for a bit of tolerance variation and it becomes virtually impossible to create a meaningful ranking in the 049 category-other than to say the Babe Bee is at one end and the TD at the other...

I have never seen-anywhere-what the Cox factory figure for SPI was-people have measured their own engines and found anything from zero to about 0.015"  -but what was the factory specification for it-and did it intentionally vary from cylinder type to cylinder type-excluding of course the ones intentionally intended-such as the QZ 049-to have none.

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