Jack i dont think its so much what piston you use or what mods you have done to it. no matter what mods or what ring gap or how many ring ect ect if it wont seal its no good. Only way to know how your set up is is with a leakdown testor. I think i would even say that no matter what ring and piston combo you have if you test it with a leakdown testor with a .023 orfice and get a 100 over 100 reading with a 13 second time from valve close to 0 psi leakdown count then your gona get a stock motor with a larger 12.7 or 11.1mm venturi carb close to or around 7500 rpm.

It seems these are the most important factors.
#1 a cylinder ring combo with as little leakage as possible and
#2 a larger carb

eveything else just dosent seem to work I know others have had some gains in increasing the port timming and that just hasent been the case for me and i had done that mod twice with two different cylinders. the gains others got from this mod i think are on cylinders that are very different from mine. i know for sure your using the two runner per side and getting results close to mine with this mod so yes it probably works on that type cyl. on mine nope no cigar lol.


I started out today to do the rest of my testing. I had my engine all ready to go with the port mods and test ran recorded 7530 rpm with a static thrust of 14 lbs 2 oz. so absolutly no change there.

Next i converted to the electronic ignition. when test ran it seem to lose rpm and performance. this puzzles me greatly. I had the timming set to 28 degrees advanced as I understand how to set the timming. i degreed in 28 degree advance and set the sensor in the middle of the magnet. when test run i was getting 7280 rpm and 13 lbs 2 oz thrust.

I was able to gain back some of the power by hand tunning the timming and testing retime and test and retime and kind of adjust for performance. best i could get was 7440 rpm @ 13 lbs 13 oz thrust.

Even though the electronic ignition seemed to lose power it was so easy to start. just a light flip and man it was off and running. this thing also has a great advance curve so at idle the timming is retarded to where the idle is so smooth. yo can idle so low you can darn near count the prop blades go by. SERIOUSLY the idle and starting was drastically improved and this was worth it right there.

From here im pretty much done testing this engine. It is more than adequate for the plane im gona put it on and its getting nice out so its time to go fly.

I am gona start another conversion that can be tested on further.

With the set up I currently have there is something limmiting this engine to or around the 7500 rpm range. no matter what I do other than the making sure I have a good cylinder to ring seal and providing all the compression i can get and a larger carb nothing else works in any tangible gain in power. I dont know if there is something holding back this set up or if it has just plainly reached a point to where there is no more to get out of this engine with this CC range. it seems the only way to get more power from here is more CC.

I did check the port volume on the two runner cylinder and it has a volume with the two runners together of 2 ml. so that would be a 4 ml port volume altogether. sorry got no way to convert this to cc.
The cylinder witht the one runner port has a capacity of 2.6 ml so that would be a total port volume of 5.2 ml. interesting that my cylinder has the larger ports but yet it dosent repond to the port timming modification.

I dont know what else i can try. I do however think that if i take a stock ryobi and get it to have around a 13 second leakdown count at 100 over 100 reading and put a 12.7 mm venturi carb on it it should run around 7500 rpm. I guess this will be where i will start when I do my next test engine. I will know that alll the mods discussed here so far will do nothing to improve this number and from there i need to go new directions.