Andrew,

Go here and join the group. Then post your questions. You may have to register as a Yahoo member to join (I'm pretty sure you will). This is a very active forum and I'm sure you will find .049 glow heads available somewhere.

http://groups.yahoo.com/group/049Collectors/

John

        Andrew, the newer slit type cylinder have been around for a long time. I first saw these in the early eighties. I noticed then the performance of the Babe Bee was quite powerful. This is due to the dual bypass ports inside of the lower portion of the cylinder. This gives considerably more power then the older Bee cylinders which were single ported. Single ported engines though will give you a lot more longevity in run time though. Some of the Golden Bees had the single ported cylinders. These cylinders typically have the #2 stamped on them. Cox did make dual bypass cylinders back then and they usually were stamped with #1. The slit style cylinders also known as production or Sure Start engines do provide some good power. The main thing is that the quality control is a bit lacking. The cheap price makes up for it though and you can purchase a few and pick the best runners from there. The open type cylinders are generally older and I've found the quality to be better. If you have a dual bypass cylinder with open exhaust I would consider that a keeper. These were used on Black Widow engines and make a great deal of power. These piston cylinders can also be a bit expensive. You can also purchase a Tee Dee cylinder which is open exhaust 2 bypass ports and 2 transfer ports as well. Those pistons are lightened and the cylinders have a taper to them.  Those cylinders usually have the #4 stamped on them. They would be your highest performance pistons cylinders available for Cox today. You can benefit using them on a reed style engine, but your going to see its top performance on a Tee Dee engine. I've seen Tee Dee's hit close to 26k which I don't recommend due to part failures. Some suppliers are also offering a lightened and trimmed piston cylinder combo. These are made from Sure Start piston cylinders and these can add another 1000k to your engine. This style is known as SPI. This means sub port induction. These work well and don't break the bank in purchasing a set. Ken

I think the slit type is supposed to reduce the likelihood of the fuel flashing off and starting a fire.  But there's more to it than that.  The Wikipedia entry on Cox engines is certainly comprehensive, but I can't vouch for its authenticity.

http://en.wikipedia.org/wiki/Cox_049

Hi guys,

I can vouch for the authenticity of that Wikipedia page http://en.wikipedia.org/wiki/Cox_model_engine, because I wrote it.  It is an accumulation of the knowledge I have learned from various sources including but not limited to:

• 049 Collectors Forum: http://groups.yahoo.com/group/049Collectors/
• Martin Hepperle's Cox Engines site: http://www.mh-aerotools.de/airfoils/cox_frameset.htm
• Former Cox employees like Larry Renger who is a member of this forum http://www.modelaircraft.org/files/RengerLarry.pdf
• Model Engine News http://modelenginenews.org/
• Cox Catalogues and price lists, of which I have copies of most from 1955 to 2000
• Tim Dannels' and Dan Sitter's Cox Articles from The Engine Collectors Journal http://www.modelenginecollecting.com/Cox%20Web%20Material/Cox-Book.html
• and of course my own experience and obsrvations

As mentioned at the bottom of the wiki article.

Now, to answer the original question...  The answer isnt a simple one... What is more important than the type of exhaust port the cylinder has, is what engine the cylinder and piston were designed for.  ie the bypass porting inside the cylinder, whether or not it has SPI (Sub piston induction) and whether or not the cylinder has a tapered grind. Tapered grind refers to it being smaller at the top to tighten piston fit at tdc.  The only cylinders that are [intended to be] tapered grind are the Tee Dee, Killer Bee and Venom, (and some Black Widows.)

As for the porting, the Tee Dee porting has two boost ports or grooves that extend beyond the original port grooves. This apparently assists with improving the atomisation of the air fuel mixture by creating a vortex.

The Killer Bee whilst being a slotted exhaust, also has SPI, a tapered grind and one bypass boost port on each of the two bypass ports.  This particular way of porting was thought to be better than the Tee Dee porting for reed valve engines, hence why it was used on the Venom. (which the prototype used a Tee Dee cylinder).

Confused yet?  The slit exhaust was designed to stop fires and was used after they tried various screens attached to the cylinder and found them to be too difficult/costly to manufacture.

Most slit exhaust cylinders you will see on bee type engines will have no SPI, and have one or two bypass ports and my or may not have a bypass booster on each bypass depending on when it was made and what engine it was intended for.
 
So before you decide which one you will use I would look at all of the above factors.

Cheers