I appreciate all the hard work everyone is doing here to come up with the best combo and/or ideas for the Ryobi. But I want to make something that is very important clear. The very first thing one should do before modifying an engine is to make sure it is in perfect shape to begin with, especially as regards to the ring seal. I have personally seen engines gain over 600 rpms with just a ring change, and even more so with the Ryobi in the case of those that do not have rings that overlap the retaining pin. Once again, the recommended ring gap in other, similar engines is .003" which is about the width of a piece of paper! It is just basic good practice when modifying engines of any type to get a good seal on all important parts before starting with modifications. Then you can get a good, honest baseline to work with, and go from there. Without a "given" of a good ring seal, all the results and comparisons you all are getting will be "all over the board" and not realistic/significant.
This is so true. Also the ring is only as good as the bore it is bieng asked to run in. In Absolute perfect conditions we shoud even have a brand spanking new cylinder. This is impractical for most of us though. I know the testing isnt perfect and we arent all gona end up with the exact same numbers. i think in this format of testing the ting to look at is the difference in the rpm of the run before the mod and the rpm after the mod. What we are really trying to find is did it increase power and how much. And yes it is gona bee all over the board.
I've had trouble getting a steady reading on my tach. It normally jumps around plus or minus 40 rpm. I'm not sure how much of this is instability of the motor itself or whether the tach is not getting every pulse of the prop blade. When I test it on a 60 cycle electric light bulb it's dead on. The APC prop is gray, a pretty neutral color, so maybe the sensor has a hard time picking it up against the background. Maybe if I took a black marker and colored it up it would help. I'll have to try that! The tach I've got is a "GloBee" from Tower Hobbies but I'd bet all the R/C marketed tachs are basically the same.
I also have a glowbee and have the same trouble. If i put my finger over the sensor it reads zero. if i put my finger over the sensor and hold it near the ignition it jumps all over the place. I am thinking of going to a hall effect sensor type tach tor testing purposes. Also im not doing and more testing to I get my static thrust unit built as i think this is gona be far more reliable info.
I think it's more likely an inertia problem. The reed has got to change direction 7000 times a minute. That's over a hundred times a second! I bet with so little spring force on the reed it's lagging behind in getting back down to the seat as the crankcase pressure builds up on the piston's down stroke. In fact it may be still on the way up as the crankcase pressure turns around from negative to positive!
I though of this to but the rubber reed valve you could open by merely blowing on it. it had no spring action whatsoever. I will try to get some measurements as now i know how you did it. i think my scale goes to a tenth of an ounce. but im not sure.
As for the newer style cylinder with four transfer runners, I believe there are huge gains to be made by smoothing out the entrance to the transfer ports. The flow coefficient, and thus the effective flow area, of those ports just has to be abysmal with those blunt facing surfaces facing the flow. I not only bullet-nosed the web separating the two runners but also matched the outer edges of the ports to the crankcase so nowhere are there forward facing steps in the flow path. I bet you are right about the difference in cylinder volume (compared to the older cylinder, ie compression) but I'm not sure how to improve that situation with my setup. The only other cylinder I've got is the one with decompression slots.
I really dont understand why they went to the two runner set up. There is an absolute visisble difference in the combustion chamber and compression volume. If i come across a cylinder like i have got i will send it to you so you can do some comparison on it. All the port designs so far have been just like you say abysmal.
I got the parts from ajonr today. I got one of the engines with the small crank case and shrouded reed valve. I am so excited about this engine as i think its got lots of potential. Thanks anjor i cant wait to play with all this.
I think after i am done with this engine in the test peramiters i have laid out i think im gona do it again with a whole new set up and see if the results are simmilar or repeatable. I am about to get into some areas with engine that i have never seen done on the net before. not saying its never been done just saying i havent seen it so it should be interesting.