Cox cylinder question
#1
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Cox cylinder question
Some of the Cox reed-valve engines have 2 slits on either side of the cylinder. But most of these engines have just a large port on either side. What is the difference? Is there more or less power produced?
Thanks,
Beeza
Thanks,
Beeza
#2
RE: Cox cylinder question
The slits where introduced for safety reasons (I think). In terms of power, it is the inside that counts, the slits doesn't seem to hinder that much.
#3
RE: Cox cylinder question
ORIGINAL: Mr Cox
The slits where introduced for safety reasons (I think). In terms of power, it is the inside that counts, the slits doesn't seem to hinder that much.
The slits where introduced for safety reasons (I think). In terms of power, it is the inside that counts, the slits doesn't seem to hinder that much.
See lower right engine.
George
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RE: Cox cylinder question
More than once I had a POOF! from the older style open exhaust start all the fuel on the outside on fire and had to blow out the engine fire before it took out the model. And one time it even spread to my fuel dowsed hand. That time it was hand first and model next all in quick steps. Never mind the grass!
The slit cylinders are supposed to avoid this issue at the cost of very little or no power loss. My own choice is to keep using the stock of old single large port cylinders as I always found that it made it easier to prime the cylinder... which, oddly enough, is what leads to the POOF! and possible fire starting....
I have to admit that I also can't get past the idea that the bridge of metal across the cylinder port is bad for the power. As far as I know none of the Tee Dee cylinders were ever done with the two slit style. I suspect it was for this reason.
The slit cylinders are supposed to avoid this issue at the cost of very little or no power loss. My own choice is to keep using the stock of old single large port cylinders as I always found that it made it easier to prime the cylinder... which, oddly enough, is what leads to the POOF! and possible fire starting....
I have to admit that I also can't get past the idea that the bridge of metal across the cylinder port is bad for the power. As far as I know none of the Tee Dee cylinders were ever done with the two slit style. I suspect it was for this reason.
#5
RE: Cox cylinder question
Supposedly, there will be no power loss with the twin slit cylinders. But, after reading the posts, I thought I would just check to see how much of a restriction might be imposed by the slit exhaust.
The BW I measured was an earlier version with metal backplate and red spinner, no cylinder number, minimal SPI, wrench flats on top cylinder fin. Port height was .115" .
I had two Surestarts handy with twin slit exhaust, no cylinder number, no detectable SPI, wrench flats on top fin.
SS #1: Top of upper port to bottom of lower port: .095"; slit height: .026" for maximum opening of .052"
SS #2: Top of upper port to bottom of lower port: .103"; slit height: .029" for maximum opening of .058"
So, on both twin slit cylinders, exhaust area was approximately half that of the BW. I also checked the length of the ports on all three engines and they were essentially the same.
There may also be some timing differences, but I didn't pull the cylinders for a measurement.
The BW I measured was an earlier version with metal backplate and red spinner, no cylinder number, minimal SPI, wrench flats on top cylinder fin. Port height was .115" .
I had two Surestarts handy with twin slit exhaust, no cylinder number, no detectable SPI, wrench flats on top fin.
SS #1: Top of upper port to bottom of lower port: .095"; slit height: .026" for maximum opening of .052"
SS #2: Top of upper port to bottom of lower port: .103"; slit height: .029" for maximum opening of .058"
So, on both twin slit cylinders, exhaust area was approximately half that of the BW. I also checked the length of the ports on all three engines and they were essentially the same.
There may also be some timing differences, but I didn't pull the cylinders for a measurement.
#6
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RE: Cox cylinder question
The Cox engines have twice the exhaust port area of much higher performing engines..so I don't see any "magic" being performed by this feature. The dual exhaust port arrangement probably helps maintain cooler running and more even cooling...keeping the ball socket happy?.
Exhaust gas is under such high pressure that crude porting designs aren't improved much with "custom" work [work that doesn't effect timing].
I'd like to see before and after tach readings [with a high revving prop] where the engine is left stock for run #1, then run #2 has one of the exhaust ports blocked off.
Have run #3 with the exhaust port blocked off and turn the area beneath it into an intake bypass port. I'll bet someone somewhere has already tried this.
If nothing else, the 2nd exhaust port gives extra sub piston induction area.
Exhaust gas is under such high pressure that crude porting designs aren't improved much with "custom" work [work that doesn't effect timing].
I'd like to see before and after tach readings [with a high revving prop] where the engine is left stock for run #1, then run #2 has one of the exhaust ports blocked off.
Have run #3 with the exhaust port blocked off and turn the area beneath it into an intake bypass port. I'll bet someone somewhere has already tried this.
If nothing else, the 2nd exhaust port gives extra sub piston induction area.
#7
RE: Cox cylinder question
I haven't bother testing the differences scientifically, we have absolutely zero 1/2A racing events here, and the only one running cox engines (occasionally) is me. Plus, once I got a taste for running Norvel engines it is very hard to go back...
Running with exhaust throttles on the cox engines, one can see just how little exhaust area that is really needed. It fact these engines are hard to throttle down, the slightest leak around the exhaust and they run at fairly high rpms.
If anyone really wants to make some "scientific" test, one can now obtain three different types of cylinders from coxengines.ca ;
i) regular sure start (twin slit, no SPI)
ii) regular sure start with the "bar" removed (no SPI)
iii) regular sure start with the "bar" removed, and aditional lowering of the port to give SPI
That way the internal transfer porting would be identical (two ports and two boost channels) and the exhaust would be the only difference.
Running with exhaust throttles on the cox engines, one can see just how little exhaust area that is really needed. It fact these engines are hard to throttle down, the slightest leak around the exhaust and they run at fairly high rpms.
If anyone really wants to make some "scientific" test, one can now obtain three different types of cylinders from coxengines.ca ;
i) regular sure start (twin slit, no SPI)
ii) regular sure start with the "bar" removed (no SPI)
iii) regular sure start with the "bar" removed, and aditional lowering of the port to give SPI
That way the internal transfer porting would be identical (two ports and two boost channels) and the exhaust would be the only difference.