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Building Tips and technical articles. => 1/2 A building. => Topic started by: Andrew Tinsley on July 21, 2011, 02:36:16 PM
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A propos of my earlier thread on a Black Widow, Just how much power is lost with the later two slit exhaust compared with the single large exhaust? If it is appreciable then milling out the bridge between the two slits seems a simple solution. I notice that Xenalook are doing this with product cylinders to supply the TD market. Is it just looks or are there serious power gains to be had? My first reaction is yes there is, but I am betting on not too much of a difference!
Regards,
Andrew.
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Try a few of each and see? Xenalook is probably smart enough to know that you don't make money selling the customer what they need, or even selling them what they want -- you make money by selling the customer what they think they want, and what they'll pay for. If that's TD cylinders with uselessly big* exhaust ports, then that's what you sell.
* And no, I don't know if that makes a difference or not.
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I never quite figured out the theory of the slit exhaust. Maybe it had to do with a cheaper cutoff tool.
I've always had a theory that Cox engines had way too much exhaust area and not enough intake. A modern schrurle ported engine has three times as much intake as exhaust. The Cox is the opposite.
My belief is that most of the exhaust gas & noise exits the engine as soon as the exhaust cracks open, so when it opens means more than how long it stays open.
Cool, low pressure incoming air needs a BIG passage. High pressure exhaust will find its way out from the smallest hole. If had the machinery, I'd like to have a Cox cylinder with one exhaust port left closed and the area used for a third (really big) intake bypass.
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I believe the slit type cylinders were designed for fire protection. Earlier attempts used the welded wire screen on the cylinder. I suppose that the slit restricts the flame from jumping out on start up. The slit type cylinders have a slightly different porting arrangement than the standard Black Widow cylinder. If you look up inside you will see what appears to be 2 ports just like the Black Widow, but each port is divided . It looks like you have 4 channels. This is what I believe is what is known as the transfer port which was typical of TD cylinders. The older TD's had the tapered cylinders as well. Some of my older TD pistons have a oil hole also located on the bottom of the rod. I feel the Sure Start cylinders work very well, but they're all not up to par. I noticed that when I purchased some of them for $5.00 when Estes was unloading them. 1 out of 4 though were doing pretty well. They certainly have tremendous ball socket play for new piston rod assemblies. I generally get around 19k + when using the Sure Starts but my Black Widow's do better than that. Ken
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hi Kenneth,
I never really realized how much the "play" in the ball socket joint of the rod/piston meant on the Cox engines until I got a resetting tool. A tightened ball socket joint does give more rpm! ;D
Big Bear
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hi Kenneth,
I never really realized how much the "play" in the ball socket joint of the rod/piston meant on the Cox engines until I got a resetting tool. A tightened ball socket joint does give more rpm! ;D
Big Bear
More important: You won't beat a hole through the top of the piston. That's what it took for me to buy a resetting tool.
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Ken, your correct. The slit type exhaust port was to reduce the chance of fire.
If your planning to operate the engine at very high RPM you will see a slight drop in RPM...but we're talking top end RPM and above of what the engine was designed to operate normally. If your building a Mouser I would not use a slit type cylinder, if it's gonna pull a stunter or for sport they're great.
Mark
http://groups.yahoo.com/group/049Collectors/