Tee Dee cylinders / 2 boost ports vs. 4

Cox International Thu Apr 12, 2012 1:57 pm

cribbs74 wrote:
So, for the record then......

Your TD cylinders have 2 bypass and 2 boosters on each bypass for a total of 4 with no taper?

That is what my TD .049 and .051 have that were bought by me in 1992. I also have an early .051 that I suppose I should check to see if it's tapered!

You also show out of stock on your site is that the case?

These cylinders have per each side:

One large channel (2 in total)
One narrow channel (2 in total)

and are identical to the #4 stamped TD cylinders we bought from Cox some years ago in bulk (their remaining stock).

What you are referring to are the ones with the total of 6 channels inside. I may be mistaken in that perhaps those were made into the ealy 90's.

There seems to be one huge misconception in regards to the 6-channel version. Allegedly, the 4-channel version performs better. Below is a (verbatim) copy and paste from an email from Larry Renger (former Cox engineer) who was involved in the TD cylinder design.

As to out of stock, don't know what you mean. here is a link to the listing:

http://coxengines.ca/cox-.049-tee-dee-cylinder-and-piston.html

We found the two boost port version ran higher rpm than four. The reason is that it introduces a swirl to the mix that enhances combustion. Four ports are too symmetrical. This trick was used in the Killer Bee, Tee Dee and Venom. I picked up the hint from the “Two Stroke Tuner’s Handbook”, a long out of print 2-stroke bible.

fit90 Thu Apr 12, 2012 2:07 pm

Is there any known advantage or disadvantage to the tapered bore? Also, do you know why it was dropped?

ahrma_581 Thu Apr 12, 2012 2:14 pm

fit90 wrote: Also, do you know why it was dropped?

I would bet, as with so many other things these days, the reason is cost..

**Admin** Thu Apr 12, 2012 2:18 pm

Some Close ups of Bernie's TD cylinder. I was going to pull the cylinder off my TD but I have all that picked in a box right now (so it is out of my way while cleaning the basement).
Tee Dee cylinders / 2 boost ports vs. 4 Flutes10

Tee Dee cylinders / 2 boost ports vs. 4 Flutes10

Tee Dee cylinders / 2 boost ports vs. 4 Spi_be10

Cox International Thu Apr 12, 2012 3:08 pm

fit90 wrote:Is there any known advantage or disadvantage to the tapered bore? Also, do you know why it was dropped?

Although the last Cox product manager asserted to me that the taper makes no difference I would disagree. I believe that a tapered cylinder, everything else being equal, would perform a bit better. How much better and if this is justified by the higher cost remains debatable.

But, taper is only one factor for performance. There are so many other variables that come into play and a properly matched un-tapered cylinder can well outperform a not-so-well-matched tapered cylinder.

I would think that cost was a reason Cox went to straight-walled cylinders.

**Cribbs74** Thu Apr 12, 2012 3:09 pm

Good to know Bernie thanks.

Like I said I purchased mine in '92 or somwhere around there. So it makes sense. Apart from milled fins or no milled fins and cylinder diameter, I had no idea there were any different designs.

I must have been mistaken about the out of stock. Sorry if I started any nasty rumors! lol!

Cox International Thu Apr 12, 2012 3:10 pm

Subitted by a customer:

Hi,
I think I have it. The reason for the 4-boost port Tee Dees not making as much power as the 2-boost port Tee Dees is probably because the transfer ports expel out the air/fuel mix so close to the exhaust ports, so some of the un-burnt fuel goes straight out the exhaust. The Surestart has only 2 boost ports, AND the main port and the boost port is fairly centered. They (the transfer ports) have about .8 and 1mm on each side of the transfer ports before you run into the exhaust ports on either side. The Tee Dee has 4 boost ports, as well as the main port and it is perfectly centered between the exhaust port, leaving a very small amount of metal (about .4- .5mm) between the upper part of the boost port(s) and the exhaust port.

In the Two-Stroke Tuner's Handbook this is on page 118 and 119 (go by the number at the bottom of the page, not the PDF page numbers) and it is referred to as "short circuiting".

I hope this helps you.

Timothy

John Goddard Thu Apr 12, 2012 4:32 pm

!!!!!!!!Don't buy Bernies TD cylinders!!!!!!!!!!
Cos
I want them all
lol!

I've bought 3 sets so far and boy do they work.
2100 rpm bolt on hopup over a medallion topend
and partly responsible for my snapped crankshaft last weekend.
We now know that 60% nitro isn't a good idea................. Airplane

You want more power with no Faffing around?
Bernies yer Man.

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Tee Dee cylinders / 2 boost ports vs. 4

Tee Dee cylinders / 2 boost ports vs. 4

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Re: Tee Dee cylinders / 2 boost ports vs. 4

Re: Tee Dee cylinders / 2 boost ports vs. 4

Re: Tee Dee cylinders / 2 boost ports vs. 4

Re: Tee Dee cylinders / 2 boost ports vs. 4