Between cox cylinders with the large exhaust ports and dual intake transfer ports, whats the difference? I have always kept the piston matched to the cylinder, but used the assemblies interchangeably. The two blackwidows i have were actually car engines. I put prop drive washers and ordered blackwidow tanks and carbs for them and installed hi compression heads. Did a factory black widow have something more?
  I also have a collection of the cylinders with the slit exhaust ports and have ignored them. How do they run?

Larry Renger is really someone who can authoritatively answer this question.

Here are a few points as I remember them. Some may be incorrect:

Transfer ports: Since the time of the Space Bug Junior, Cox has used one transfer port for sport engines and two for power (Space Bug and Thermal Hopper at that time). The single transfer port worked better with the smaller venturi which provided easier starting and better fuel draw...good for beginners. I believe this was carried through until near the end.

The extra boost in the TD cylinders was an improvement, not on the first ones.

The exhaust slot top and bottom locations were/are positioned for timing. Which way they are pointing is arbitrary.

TD cylinders were tapered for higher performance. Early Black Widows used TD cylinders.

Black Widows used the "stunt vented" tank setup from the Golden Bee, but with a larger venturi for power.

Toward the last, I THINK ESTES used the Sure Start front end on an unvented plastic tank for the Black Widow, as well as the BabeBee and the Texaco.

George

Hi guys,

Firstly, let me say the info on the Wikipedia page is simply an amalgamation of information I obtained from three main sources. ie (1) Larry Renger, (2) Martin Hepperle's  http://www.mh-aerotools.de/airfoils/cox_frameset.htm and (3) Mark Boesen's 049collectors forum http://groups.yahoo.com/group/049Collectors/.  

I do have a collection including almost every type of Cox engine ever made so I have been able to make some of my own comments and observations as well as confirm information obtained from my various sources.

To answer the question, Larry is the best person to answer this question as he worked at Cox as a design engineer and is responsible for many engines and RTF planes, including the Black Widow and Venom engines.

However, I will have a go in case Larry is over answering Cox questions.  To quote Larry on the 049 collectors forum "The original split exhaust was made to prevent fires.  The open exhaust can blow flaming fuel out and start the plane on fire.  This can’t happen with the slit exhaust."

From what I have learned, standard slit exhaust cylinders have No sub piston induction. This is handy for using a muffler as mufflers degrade SPI engine performance considerably.

Early slit exhaust cylinders were same porting as Black Widows, ie dual bypass no booster grooves.  Later ones came out with a single bypass booster groove on each bypass port. However I have seen single bypass slit exhaust cylinders too. These would not be very good unless you want a lower power engine. I believe that the booster groove is an attempt to put back what the slit exhaust and lack of SPI takes away. Not sure if this is true in reality.

The exception to the above is the original Killer Bee.  Slit exhaust, dual bypass, one booster groove on each bypass, tapered cylinder, lightened piston and sub piston induction and stronger balanced crank shaft to handle extra power.
The killer Bee cylinder can be easily identified as it has a wider lower slit and you can see the SPI gap when the piston is moved to TDC.

The Venom used a cylinder similar to the Tee Dee, but it had one large bypass booster on each bypass. ie much bigger than slit exhaust bypass booster groove. (see pic) The problem with the Venom was that the piston was made too light.
 
The Tee Dee 049 and 051s had dual bypass ports with dual booster grooves (one on each side of each bypass port, tapered grind, lightened piston, SPI but NEVER slit exhaust. The 051 has a single groove in the skirt of the piston for identification purposes.

So which is best (for power), from top to bottom, Tee Dee (number 4), Venom, Killer Bee, Black Widow (number 1), Dual bypass Slit exhaust then Single bypass (number 2). IMHO.

Cheers

Warren,

Thanks for all of this. Have you seen a #4 Cylinder where it is marked in the side of the cut for the Exhaust window rather than below it like most Cylinder markings?

Mark