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  1. #126

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    That's a bummer. I can send you my old coil if it will keep the testing going, it's from a keyed crankshaft. It's a Phelon unit.
    Tommy Dale
    Racinrc14@yahoo.com

  2. #127
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I already tore it all apart and im gona use my other crank and coil. It will give me a chance to see if the timming of the two different units are tha same anyhow. I just need more time to play with it. Today was so nice i had to finish building the field roller for the club.

    Thanks for the offer though.

  3. #128
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I plan on procceding with my engine building and testing today. In a way I do it with kind of a heavy heart as I feel I was knocked pretty bad in another post.

    http://www.rcuniverse.com/forum/m_8545703/tm.htm

    I dont know if it is understood how much time and work I have in this. I think my bolts and nuts are just about worn out from assembly and disassemely plus the money that I have in this.

    I know my test procedures are less than perfect. For example today it is windy outside. I have no choise but to test outside. the tach will not work around floresent shop lights and my shop is flooded with them as i belive in a well light shop. My worry is that the wind will help unload the engine or falsly load it depending on which way the wind is and skew my test numbers.

    At this point I am wondering if this thread is even worth continuing if this is how most of you feel about my efforts. I hope that you guys understand that I never intended for this information to be a matter of fact statment of this mod will provide this and this part will provide this. I was merely listing my results for your comparison and see if others have had the same results in a little better format than it seemed to help gain power, but rather have some numbers to back up the claim of improvement. there has been lots of good ideas and exchanges of information on this post. And in my opinion while i know its not perfect i feel it has been very usefull to others.

  4. #129

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I, for one, am very appriciative of your work and hope you continue it. I have several Ryobis, one converted already with EI and am very interested in how I can get the most out of it without machinework as I do not have the machine tools. So please keep going.

    Jim

  5. #130

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    If your posting hard numbers, it ain't Pseudo-science. The reason things work may beyond some ability to understand, but the fact that it works (or doesn't work) is hard to argue with.
    Press on.
    TKG
    Too much power is just about right.

  6. #131
    av8tor1977's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I agree. Have at it and don't let them get you down. I am interested in this thread and appreciate the work you are doing, and I'm sure others do as well.

    AV8TOR
    If it is not SCARY, it is NO WHERE NEAR powerful enough!!
    All R/C planes have expiration dates---> It's just not printed on them anywhere!

  7. #132

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Since there has been a lot of discussion on different RYOBI engines, I feel it necessary to share with you some information I have collected over the years. I have studied at length three different engines, and these are the spec's as I measured them.
    Engine Bore Stroke Inside Measure on Crankcase Outside measure of Back plate (Reed Plate)
    28cc 1.32 1.28 2.2 2.1
    31cc 1.38 1.28 2.02 2.02 Early Style, recessed reed valve
    31cc 1.38 1.28 2.2 2.1 Newer style
    I have short shaft engines that have narrowl keyways on the crank, and others with wide keyways. I also have long shaft engines that have both. I have a back plate from a whip sold under the STIHL name (stamped on the WALBRO Carb Cover) that is white in color that is more square, not smooth like the the newer back plates.
    I have four different con rods, form very light weight to one that looks like it is really beefed up, but came in an otherwise stock motor.
    I am not going to address the different cylinders because there are so many different port shapes, and I haven't really got into that testing yet. However, if you leave out the gasket for higher compression, you should check the port timing and modify as necessary. You can change the port timiming by up to 5 degrees if you leave the gasket out.!!!
    All blocks are interchanglable with some minor mods. The early piston has more metal on the front skirt of the piston that can be ground down, but I don't recommend this because the early engines have a smaller counterweight, and this may be a more desireable engine in its original configuration."Don't cut up something you may regret later) "voice of experience".
    The stroke, wrist pin and journal size are all the same in the every engine I have checked.
    I will do further testing as the weather warms. Presently, I have engines turning a 20 X 6 close to 7500. I use mostly electronic ignition, but also mags. I am still using the stock Carbs with some variations, but will go bigger on my next experimenting. FLATHEAD 4

  8. #133

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Combat don't give up yet!!!! I NEED you to complete the testing so I know how to set up my conversion. I appreciate your time as I understand what it takes to do this kind of work. Unfortunately I dont have the know-how to comprehand some of the 'other' technical languages used in other posts, your language suits me fine because I understand it. If I had the time, I would do the very same thing, regardless of what other snobs might think. I have learned over the years that being an engineer makes you an idiot in the minds of the mechanics (me) who have to fix what you've designed. Please press on and continue the testing, I find it interesting and it's one of the only reasons I even log on to this website.

    Also, if you need a matched flywheel/magneto combo, just say the word. My flywheel has already been machined.....
    Tommy Dale
    Racinrc14@yahoo.com

  9. #134
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Thanks guys I do appreciate the support and makes this all worthwhile. I need your ideas as much as you need mine and really like how information is shared here.

    Flathead thanks for your input to. Thats the kind of info I would really like to see. 7500 on a 20-6? Holly smokes I would like the details on that build up. I can hardly get to 7500 on a 18-8. It would be interesting to compare what you have done to mine. are you getting that rpm with a stock ignition or a electronic conversion? I am starting to wonder is my stock ignition is a limiting factor. I cant seem to get much past 7400 RPM. When you say stock carb are you talking about the stock 7-8 mm venturi carb. If thats the case thats pretty impressive as I have found the biggest gain in power came with a carb increase. I see you are in goodland Kansas. Whats your altitude there? Its 1200 feet above mean sea level here. If your getting those results and are at an altitude between 1200 feet here and the 5280 feet of denver colorado than thats pretty impressive. I may have to come visist you on one of my trips back to denver to see my folks so we can do some side by side comparisons.

    Ok back to today testing

    I installed the crank and flywheel and coil combination from the new engine. I also refound TDC and remarked the timming marks as I had them before. I then installed the 17-8 prop and ran. I recorded a RPM of 8220. I now know at this RPM I now belive that im not up against an RPM limiter. I also tested the timming again and found that it seemed to be static set at about 29 degrees. It did not have the drop in advanced timming that was very prominent when the rpm was reduced to low speed like the other coil would. I think this made for a very rough idle. In my opinion an electronic ignition that retards the timming at idle will have a greatly improved idle quality and have lot less vibration.

    I then installed the 18-8 prop with the stock valve to get the days baseline testing numbers. I recorded 7410 RPM

    Next I installed the modified reed valve again and test ran. I recorded an RPM of 7410

    I then installed the rubber reed valve again and test ran with a recorded RPM of 7410.

    I now am wondering if in my first testing of the reed valve with the old ignition set up if my baseline reading was off somehow. I dont know how or why but i think it may have been as my readings today were all the same no matter which valve was used.

    Again in my first testing of test #7 reed valves

    stock valve RPM 7050
    modified reed valve 7410
    rubber reed valve 7410

    Second testing of test #7 reed valves

    stock valve RPM 7410
    modified reed valve 7410
    rubber reed valve 7410

    I am now thinking there is some other area of the engine holding up flow and not the reed valve. Each modified reed valve offered less restriction to flow and had no effective increase in power. In my opinion this tells me that the reed valve even in stock form can flow way more than the rest of the set up will flow. I dont know weither from here I should try to improve the intake manifold or the exhaust system. I really think my muffler flows real well as a can cover one of the two outlet pipes with no change in power. output. Also changing the port timming may help to.

    Test #8

    With all this in mind i now decided to try and reduce the thickness of the bar in the middle of the exhaust port and improve flow to see what results I could get. I did not at this time chan.ge the port timming. so after spending some time with my die grinder and narrowing this bar i Cleaned it all up and reassembled and test ran.

    Recorded an RPM of 7440. For a net gain of 30 rpm. Not much of a gain but its a step in the right direction.


    Ok to recap all this info so far

    Test #1 stock engine no performance mods. Using old 1 ring piston and newer engine with the twin intake runners per side. This should give a good baseline for a starting
    reference point.

    Recoded RPM 6300

    Test #2 Again stock engine and no perfomance mods. Using two ring piston and newer engine.

    Recorded RPM 6330 For a net gain of 30 RPM I actually expected it to be a little more than this.

    Test #3 Stock engine no performance mods. 2 ring piston and the older and looks to be higher compression combustion chamber design. If you look at the old crank case and
    look at the new one the new crankcase is just a modified version of the old crankcase ports. Therfore the ports should match the ports on the old cylinder just fine. Again the purpose of this test is to see if the higher compression help.

    Recorded RPM 6570 For a net gain of 240 RPM!!!!!!!! At this point I was not convinced this rpm gain was due to the higher compression and could have been a result of better ports.

    Test #4 Takeing the best combination of test 1-3 cylinder and piston combination. Removing the cylinder base gasket and try to increase the compression ratio some more. With the combination of piston and cylinder I have, when the gasket is removed it causes a piston to cylinder contact. I measured the height of the piston in relation to the top of the spark plug hole. If you take a dial caliper and extend it you can use it for a depth gauge at the end of it. If you hold it on the spark plug hole and rotate the crank when the piston comes to the top you will have your reading. Ok so my reading with the gasket was .610 Without the gasket it was .585 and agian there was contact. Ok so i measured the gasket and figured it moved the cylinder down .030 this means that i had a .005 interfereance fit. So i cut a gasket out of carboard stock that measured .010 . When I installed the cylinder with the gasket and remeasured it gave me a reading of .590 so I now have moved the cylinder down .020 and should have .005 clearance between the piston and the flange of the combustion chamber.

    Recorded RPM 6,660 For a net gain of 90 RPM now I am convinced the rpm gain of test three is from the higher compression as is this RPM gain is also.

    Test #5 This test takes the best results of test 1-4 and uses the crank from the old engine to see if there is a gain as it looks like this crank has more advance in it. Out of pure curiosity i took the ignition coil from the old engine and used it with the new flywheel. It would hardly run in this combination. Likewise on this test i use the old flywheel. In this configuration it runs great with the old coil but like crap with the new coil. On inspection of all these parts there are two manufatures of thses parts. The newer coil and flywheel is made by walbro. the older coil and flywheel is made by phelan. For some reason they are a matched set and cannot be inerchanged in any combination from new to old. The only way to change the flywheel is to change out cranks. Anyhow so the theory is that the older set up has an advanced timming. When the crank was changed out the seal was left on the outside nezt to the flywheel. I will try and put it on the outside of the inner bearing on test # 9 as this should reduce the crankcase volume.

    Recorded RPM 6,670 For a net gain of 10 rpm. At this point i am not sure there is any advance in this setup from the other set up. there isnt enough rpm gain to

    Test #6 I took the best results of test 1-5 and used a 12.8 mm venturi carburetor that ws purchased on ebay for 15bucks. After making the necassary modifications to the carburetor which pretty much just consisted of swaping stock parts from other carbs to make the configuration that worked best for my application I test ran the engine and had my biggest gain yet.

    Recorded RPM 7170 thats a net gain of 500 RPM !!!!!!!!!!!!!!

    first testing of test #7 reed valves

    stock valve RPM 7050
    modified reed valve 7410
    rubber reed valve 7410

    Second testing of test #7 reed valves

    stock valve RPM 7410
    modified reed valve 7410
    rubber reed valve 7410

    Test #8

    With all this in mind i now decided to try and reduce the thickness of the bar in the middle of the exhaust port and improve flow to see what results I could get. I did not at this time chan.ge the port timming. so after spending some time with my die grinder and narrowing this bar i Cleaned it all up and reassembled and test ran.

    Recorded an RPM of 7440. For a net gain of 30 rpm. Not much of a gain but its a step in the right direction.


    In my opinion the best set up so far would seem to be

    An older engine with the one ring piston and ring set up with the port and head configuration of the cylinder on the right. also using the older flywheel and ignition coil set up if your going to stay with the stock ignition as it seems to have some retarding in it at lower throttle and will help lessen the vibration at idle.



    Taking out the one ring piston tossing it and purchasing this piston and ring set up with the two rings that already have the zero gap setup.

    http://search.cartserver.com/search/...words=753-1207

    Next lowering the cylinder to the base by taking out or reducing the thickness of the gasket according to what you engine measures out to be safe to do so.

    Next installing a 11-12 mm venturi for what my test indicate to be the biggest increase in power gain.

    I dont see any need yet to do anything with the reed valve but reducing the thickness of the cylinder exshaust port will give a very small power increase yeild. it all adds up I guess.

    So far this should give about or around a 7410 rpm with what I consider to be the best of all the stock parts with no major machining modification.

    From here I am not sure where to go. My test # 9 was gona be to modify the intake manifold and maybe bell mouth it at the reed valve end. I just dont see where this will help. the intake runner is already bigger than the venturi and the limiting factor as far as max flow will be the smallest orfice sive in the system which is the venturi. simply put no matter how much bigger i make the port i cannot stuff any more air through the venturi.

    I can change port timming for my next test and may be the direction i go on this. other than flat out removing the middle bar i dont think there is anything else i can do for exshaust flow improvement.

    I am wondering if reducing the crankcase volume will improve flow as a smaller volume in the crank case volume might help in aidiing air induction. With less volume there will be less of a pressure change swing in the crank case. There will be less time or degrees of crank rotation needed to reduce the crankcase pressure to start drawing in fuel and air. The max volume will be goverend by the bore and stroke of the engine and atmosheric pressure but crankcase volume, and airflow restriction will all affect this function.

    I think My next test will be test #9 change the port timming to 150 degrees and record RPM. Next for test # 10 try and reduce crankcase volume. I need ideas on this as there isnt much room to do this modification. and for the last test I will do the electronic ignition to see what this yeilds.

    As it stands now what I have is more than adequate for what plane I am gona put it on. I would still like to see this testing out to the end.

    In a way I would very much like to get my hands on one of the smaller crankcase engines witht the recessed reed valve. I have my suspisions that this could be the best canidate for the best performance despite what is written here but till I get one I wont know for sure lol.





  10. #135

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Switch the order of your #9 and 10 test. IF stuffing the case is a simpler operation than changing the exhaust timing.
    TKG
    Too much power is just about right.

  11. #136

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Tell me what you need and an address to send to and you will get it.

    This is getting verry interresting, Please dont stop testing.I have been trying to do this for a while.You have sparked my interest in this again.

  12. #137

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Combatpilot-
    I have several cranks and carbs that might interest you if you would need one.

  13. #138
    av8tor1977's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    What is your present exhaust port timing on your best setup? I have found raising the timing from the often found 120 to 130 degree range up to 150 degrees to be very beneficial. Also, I would still like to see a comparison of going to a Frank Bowman ring. I think you will find some power in that as well.

    It takes a little power to drive the mag, both to generate the current and to move the air with the mag fins. So you will find a bit of power there as well if/when you go to CD ignition.

    My Ryobi with the base gasket left out, exhaust ported to 150 degrees, Frank Bowman ring, 11mm carb, aftermarket muffler, and electronic ignition (no magneto) turns an 18 x 6 prop at 8500 rpms. (I know this is too high for the Ryobi and will be putting a larger prop on when I get a chance.)

    The 7500 +/- rpms you are getting with an 18 x 8 prop is not bad at all, but there is still some more power to be had.

    Good luck and keep going,
    AV8TOR
    If it is not SCARY, it is NO WHERE NEAR powerful enough!!
    All R/C planes have expiration dates---> It's just not printed on them anywhere!

  14. #139

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I think a page or two ago he found it to be 140 degrees. And I think his intake duration was 130 degrees.
    Tommy Dale
    Racinrc14@yahoo.com

  15. #140
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Yep thats right racinrc14 i had a exhaust port timming of 140 degress which is actually higher than i had expected.

    Thanks for all the offers i dont know what i need at the moment. I really need ideas on reducing the crankcase volume.

    I think that may bee a good idea on the moving test 9 for 10.

    I know I need the bowman ring. Like i said in an erlier post.
    While tearing my engine down a inspecting I realized that I already had the zero gap rings with the notch to fit over the piston pin. My cylinder must be a little worn as i am getting a .019 gap on the top ring and a .017 gap on the bottom ring. I dont know if a new set would have a beter gap or if its my cylinder.
    at this rate its no quite zero gap lol

    While reading through this thread again reviewing all this info i found a post i had missed. I dont know how i missed this and he has a very good point.

    nitro joe

    "unfortunately like you say the older engine has the single ring piston which is pretty lousy. In my opinion so far the best set up is to find the older engine and then get the new style two ring piston to put in it."


    To be fair to this lowly design:

    (1) What did the end gap of this piston ring measure?
    ( 2) Was the ring face and sides free of any nicks,or scratches?
    ( 3) Condition of the bore it was asked to run in?
    (4) Did you check the ring on a surface plate ? (Glass plate with a new piece of ~ 1000 grit oiled wet/dry)
    (5) What was the piston ring groove to ring clearance?
    (6) Is the piston groove completely contamination free?(no burs,nicks,or contamination)

    Some folks call this "blue printing", measuring all the basic stuff, before messing with the mods.

    Just an old mechanic wondering....

    It would seem unfair to dismiss a design that has proven very effective in minimizing friction in countless high performance applications,due to missed concepts,with such a blanket statement.
    It very well may be the best set up would be the single ring with a zero gap and it might have the benifit of less friction. I think this is worth testing but i really dont want to spend the money on a ring for this test. i guess it wouldnt be to bad at 12 bucks but my piston is pretty scored up and i dont think it will seal well on the ring lands. I do know my numbers may be somewhat skewed as my cylinder is used and not new or perfect by any means.

    av8tor1977 what exhaust are you using on this engine? I am wondering if and when i go to electronic if mine will run right up there with yours. oh yea what prop also i think an acp prop gives very different results from a dynathrust but i just like the dynathrust look better lol.

    Do you guys think maybee my 12.8 mm venturi carb is to big. I know most guys on here go with the 11.1 mm venturi carb and seems to be the standard.

    What i am thinking for the reducing the crankcase volume is to switch the seal to where it is next to the ineer bearing rather than on the outside. this will reduce the volume in the crank shaft bearing housing. it wont let the outer bearing get lube but a sealed bearing with grease should be ok for that.

    From there I am wondering just how much farther inward i can move the backplate. I think the only way to do this is to machine the back of the case and i would rather avoid this.

    I am also thinking of machining my own backplate from a piece of plastic.

    I have some other ideas but i need another backplate and an old junk case to experiment with.

    It would be nice to be able to stuff the underside of the piston with something. unfortunatly i dont think this would let the piston cool properly.

    Ajonr might you have another backplate and a junk case? mybee even a 11 mm venturi carb for comparison?

  16. #141
    av8tor1977's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I run mostly APC props, but a Zinger is what happens to be on my Ryobi at the moment.

    Before worrying about other methods for stuffing the crankcase, I would make the bearing/seal change and see if the engine responds well first. You can't move the backplate inward on the engine much because the reed valve stop will hit the crank pin.

    Once again, with the ring gaps you are running you would see a nice power gain with a Frank Bowman ring. 12 bucks isn't that much in the grand scheme of things... (Just my two cents here.)

    AV8TOR
    If it is not SCARY, it is NO WHERE NEAR powerful enough!!
    All R/C planes have expiration dates---> It's just not printed on them anywhere!

  17. #142
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    In your post about the reed valve mod, I think that the transfer port size is holding u back. On the newer jug, the ports are very narrow. On my jug, i removed the metal between them completely. I have not been able to test the mod yet (its just too dam cold here in canada) I have been told that the mod might cause problems with the rings not being properly supported. As soon as i can get this engine running, i will post a video. The only other mods to my engine are bigger carb, modified muffler (just drilled two 1/2" holes) exhaust changed to approx 150 degrees, and the transfer port mod.
    To stuff the case, if you were to machine a new backplate, you could have a recessed area that would clear the conrod and crank pin. Just be careful when stuffing. I blew up a homlite 25 doing that. the plate that i used was too close to the crank pin, and when the metal expanded, the pin gouged it and the metal pieces jammed and broke the ring. It was spinning at about 9000 rpm when it did this, so it made one hell of a bang.
    I hope they serve beer in hell!

  18. #143
    Twin Star's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    CombatPilot
    Who do you get to mill your flywheels and other parts. I'm in SW Mo. and I'm wanting to try a conversion project.
    No engine parts were deliberately harmed in this process.

  19. #144

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I guess I had missed the post "SLAMMING" you. I feel that we all have info to share, and promise you my support. If you haven't guessed by now, my emphasis has been on "Stuffing" the crankcase. That is why I have mentioned the different back plates and reed valve arraingments. I cannot determine to date if smooth back plates, or partially inclosed reed valves are best. I do know that the early crankcase gives me best performance to date. I am adding additional material to the backplates from the "STIHL" labeled units because are smooth and easy to add material. I am fighting a severe infection at present, so my testing is on hold, but it don't stop my thinking process. I am at 3650 ft elevation, which makes a difference also. Keep up the good work, and keep us informed. FLATHEAD 4

  20. #145
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Quote Originally Posted by diceco

    combat....

    You are doing some very meticulous experimentation on the Ryobi engine and being a Ryobi flyer I'm very interested in what you find out about them.

    One of the questions I have is what effect the "side decompression slots" in the cylender walls actually have on performance. I was recently given a Ryobi trimmer that has a single ring, old style transfer ports and a long shaft, exactly my preference for the Ryobi motor EXCEPT it's got those little slots in the cylender walls, which CAN'T be good for performance..... but I wonder what the real measured effect is. It may not be as bad on one would think.... or maybe it is! Have you or anyone else ever done a performance comparison to measure the effect?

    diceco
    Combatpilot.... Your work has inspired me to do some experimentation on my Ryobi motor. I have been flying it in a GP Giant Super Sportster for about a year. It flies ok but it could use some more power.

    I yanked it out and put it on the test stand today and ran a couple of tests.

    First off it had a very small carb on it with a venturi size of only 7 mm. I had an 8 mm venturi carb from another Ryobi WW so I put that on it. I have difficulty getting a stable reading of RPM but I think it gained about 50 RPM. I did not do a baseline today for the small carb but have used data from a run done in November installed in the airframe. The measured thrust went up about 1.1 pounds from 11.5 to 12.6. As I said one test was done in the airframe and one on a test stand so there is possibly a difference there. These data are corrected to sea level standard conditions as outlined previously.

    I next put on the old style cylinder with the single runner transfer ports and the decompression slots cut above the transfer ports. The piston was a two ring and the crankcase the later configuration designed for the two runner cylinder. By your observation the cylinder head volume may be smaller too ie greater compression. The performance was abysmal!! It lost 630 rpm and required a lot richer mixture but boy did it idle nice! It got down to 1300 RPM before it started missing, but it still didn't quit! Needless to say idle is not the operation point we are most interested in is it! The obvious conclusion is that a cylinder with decompression slots makes a good paper weight!!! I'm not confident enough of a positive outcome to try filling the slots with anything.

    The results of your testing point to a bigger carb as the very first thing I need to get improved the power. BTW when you all speak of carb size, eg. 11 mm, are you talking about venturi size? Also I noticed that even on the stock carb that came with the WW that the intake manifold dia is greater than the carb bore. You'd think that it would be of great benefit if the two were the same although with the aft facing step there is almost no loss in flow coefficient although the flow will decelerate.

    Also, what do you suppose the benefit of cutting a waist in the reed is? More flow area when the reed is lifted? Also I notice that, at least for the backplate that's apart on my bench, the reed seat is not flat. The reed is suspended over a concave surface so that when closed there is space between the reed and the seat in the middle of the flat reed. In this configuration there would have to be some crankcase pressure to close the port to the carb. Is this the way they're supposed to be? I would think that if the reed were completely closed at static condition it would work better, but then again this is all a guess. I see in your most recent post that on your second reed test there was no difference in the modified reed so perhaps the question is academic.

    One other thing. When I first saw the newer style two ring double runner transfer port cylinder design I couldn't believe there were blunt forward facing steps at the entrance to the transfer ports. That certainly would make a very lossy entrance flow coefficient. I just had to try and improve the situation. Unfortunately I did not do a back to back test to see what the performance difference was.

    diceco

    PS. There are always some sour grapes in the bunch. One needs to just throw those away and enjoy the rest of the grapes! I for one am glad you are publishing your findings in this forum.
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  21. #146
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Wow what a lot to reply to. I would have replied erlier but i was at the rc swap meet. I ended coming home broke but i got rid of a bunch of stuff I was never gona use and gained a zenoha g63 for 50 bucks. he says the crank is bent and needa a new one. this crank is a three piece crank all pressed together just like a motorcycle crank. Its not to hard to straighen it back out as it just slipped on the rod journal pin. I then needed a plnae to put it on so i scored a new in the box sig sun dancer arf for 225. man is my wife gona be peved lol. needless to say im broke again and this sure wasent the intent for the day but I just could not resist.

    Dieco thanks so much this is the kind of comparision I would very much like to see.

    I do not have a cylinder with the side decompression slots so i cannot do any comparison on this set up. I just dont see how this could be good for performance. If a larger gap on the rings of .030 makes a difference than i cannot see that the slot would not make a difference. they are in affect leaking compression back into the crankcase just like a larger gap in the ring would do and we already know this is not good.

    I have difficulty getting a stable reading of RPM but I think it gained about 50 RPM.
    this is interesting as I also have difficulty getting a stable reading and I am wondering if the ignition is affecting the tach. I am thinking a thrust weight testing might be more accurate for this but i have no way to do this and really dont want to take the time to fab something up. I would like to see how you do your test this way. I ussually have to work at it for a while till i can get a stable reading and go with that number. it takes a little fooling with but i feel i have been pretty consistent in my method.

    I next put on the old style cylinder with the single runner transfer ports and the decompression slots cut above the transfer ports. The piston was a two ring and the crankcase the later configuration designed for the two runner cylinder. By your observation the cylinder head volume may be smaller too ie greater compression. The performance was abysmal!! It lost 630 rpm and required a lot richer mixture but boy did it idle nice! It got down to 1300 RPM before it started missing, but it still didn't quit! Needless to say idle is not the operation point we are most interested in is it! The obvious conclusion is that a cylinder with decompression slots makes a good paper weight!!! I'm not confident enough of a positive outcome to try filling the slots with anything.
    now this is very interesting as I had a pretty large gain in power. now this is some good comparison thanks so much. The only thing is I donot have the decompression slits in mine. so i cant really tell what the difference is. Now im wanting one of these cylinders with the slots just for comparison sake.

    The results of your testing point to a bigger carb as the very first thing I need to get improved the power. BTW when you all speak of carb size, eg. 11 mm, are you talking about venturi size? Also I noticed that even on the stock carb that came with the WW that the intake manifold dia is greater than the carb bore. You'd think that it would be of great benefit if the two were the same although with the aft facing step there is almost no loss in flow coefficient although the flow will decelerate.
    Yes i do mean the venturi size. If you go back through this thread you will find where you gan get the size from the carb number. I think I folow you in the loss of flow coefiecent. I agree it would be of benifit if they were the same size as this would give a more consistent velocity. Just as long as the venturi is not larger than the intake runner. I just dont see where this would work. if you get the 11 mm carb you will notice the outlet end of the carb is the same size of the intake runner port.

    Also, what do you suppose the benefit of cutting a waist in the reed is? More flow area when the reed is lifted? Also I notice that, at least for the backplate that's apart on my bench, the reed seat is not flat. The reed is suspended over a concave surface so that when closed there is space between the reed and the seat in the middle of the flat reed. In this configuration there would have to be some crankcase pressure to close the port to the carb. Is this the way they're supposed to be? I would think that if the reed were completely closed at static condition it would work better, but then again this is all a guess. I see in your most recent post that on your second reed test there was no difference in the modified reed so perhaps the question is academic.
    As far as cutting the waist are you reffering to the modified reed valve i tried in the second part of the reed valve test? if this is the case the idea was to reduce the pressure it took to unseat the valve and causing a decreased restriction to flow. i dont know if it would create more flow area or maybee it would if the valve were to lift higher. It needs to be understood that to move the air gas mixture there has to be a difference in pressure. Sorry but there is no such thing as vacumme. except outer space and in your wifes closet. so it is not vaccume that draws the air in but it is atmospheric pressure that pushes it in as it is at a higher pressure than the pressure in the crankcase caused by the upward stroke of the piston. the upward stroke also causes a pressure differential. things in nature flow from high to low in the path of least resistence. So the idea was that with the modified valve it will take less pressure differential to open the valve and would cause more air to flow as the valve opens sooner and the air will flow with less resistance. remeber the path of least resistance. so in affect the pressure of the crankcase will be higher when the piston starts to compress on the downward stroke than if the valve causes a greater path of resistance to flow like the un modified valve. That was also the idea of the rubber valve as it is supper easy to open and has a very small path of resistance to the airflow. Does this make sense or did I not explain it good. Im sorry if thats fuzzy i know my comunication skill at times need work. If you have two reed valves modify one and make a rubber one also. if you put your mouth on the intake runner where your lip covers the very small pulse port for the fuel pump and try to blow through each one you will see what I mean. This is how is what i did and the difference is quite visisble although it dosent taste to well lol. I dont think the no power output results to be academic as i take it to indicate that there is a resrtriction to flow elsewhere where this mod makes no difference. it may make a difference if this flow problem is found and found to be a problem so it is good info to put in the cranial file cabnet and may yet be usefull latter.

    I also had a reed tah was not flat on the backplate and i adressed this in the beginning of the post.

    The second discovery is that when I bent the reed valve stop it bent close to the screws which relieved the stop out towards the intake hole. If you look at it from the side it does not allow the reed valve to completely sit flat with the back plate and you can see a small gap between the valve and back plate. The back plate has kind of a swoop up cast into it where the reed valves sits. It is impossible to get a picture of this as I have tried lol. I don’t know how I didn’t catch these problems to begin with. Just not paying attention I guess.

    Ok so where do I go from here. I think my first step is to modify the back plate that goes with this engine without any performance mods. This will give a stock and correct crankcase volume. I then need to bend and modify my reed valve stop to where it holds the valve flush with the back plate and has the 1/8" gap. I think if you’re going to bend this reed valve stop the best thing to do is to put it in a vice as close to the bend as possible and bend it there not up close to the screws. Check your reed valve when you do this to make sure it still sets flush. I will then test run this engine again in this configuration and get a good starting point. From here I can begin to modify.
    form flathead
    If you haven't guessed by now, my emphasis has been on "Stuffing" the crankcase. That is why I have mentioned the different back plates and reed valve arraingments. I cannot determine to date if smooth back plates, or partially inclosed reed valves are best. I do know that the early crankcase gives me best performance to date. I am adding additional material to the backplates from the "STIHL" labeled units because are smooth and easy to add material. I am fighting a severe infection at present, so my testing is on hold, but it don't stop my thinking process. I am at 3650 ft elevation, which makes a difference also. Keep up the good work, and keep us informed. FLATHEAD 4
    Those kind of numbers at 3650 ft is pretty damn impressive. Yes i can see you are wanting to stuff the crankcase lol. Im right there with ya on that one. When you say erlier crankcase do you mean the one that has the smaller dia and the shrouded reed valve backplate. If so i have said in my opinion this may be the hot set up. the smaller dia crankcase = less crankvolume. the shrouded reed vanlve means there is more backplate stuffed into the crankcase making less crankcase volume. also look at the counterweight on the crank. its the one on the left to me this screams less crankcase volume.



    I think this picture speaks volumes. the one on the left is quite visibly smaller. if the end of the reed stop is the same depth or didstance to the rod then the one on the left definatly has more material in the crankcase ==ing less crankcase volume. I know it looks like it wont flow as well but from what your numbers indicate the not as good flow is offset by a large gain in less crankcase volume. also notice the relief cut in the backplate where it clearances the cylinder. the one on the right is cut at an angle and would seem to me to have lees material to take up crankcase volume. this is just my opinion and i would really like one of these motors for testing.



    In your post about the reed valve mod, I think that the transfer port size is holding u back. On the newer jug, the ports are very narrow. On my jug, i removed the metal between them completely. I have not been able to test the mod yet (its just too dam cold here in canada) I have been told that the mod might cause problems with the rings not being properly supported. As soon as i can get this engine running, i will post a video. The only other mods to my engine are bigger carb, modified muffler (just drilled two 1/2" holes) exhaust changed to approx 150 degrees, and the transfer port mod.
    To stuff the case, if you were to machine a new backplate, you could have a recessed area that would clear the conrod and crank pin. Just be careful when stuffing. I blew up a homlite 25 doing that. the plate that i used was too close to the crank pin, and when the metal expanded, the pin gouged it and the metal pieces jammed and broke the ring. It was spinning at about 9000 rpm when it did this, so it made one hell of a bang.
    You very well may be right on the transfer ports holding me back. I have looked very closelly at the cylinder with the two runners per side and have concluded that even with the runners being smaller colectively they are very close in volume to the single runner ports. I really dont understand why they did this and would really like to hear it from the engineers mouth on this one. I am very interested to see how you rengine responds to the removal of the metal between the runner ports. I hope you dont take this wrong But i think even if it does improve its not gona be as good as the single runner cylinder as it has a higher compression ratio. in my opinion widening the runners of the higher compresion cylinder may be the way to go. Point well taken and appreicated on the bang warning lol.

    Before worrying about other methods for stuffing the crankcase, I would make the bearing/seal change and see if the engine responds well first. You can't move the backplate inward on the engine much because the reed valve stop will hit the crank pin.

    Once again, with the ring gaps you are running you would see a nice power gain with a Frank Bowman ring. 12 bucks isn't that much in the grand scheme of things... (Just my two cents here.)
    Im right there with ya on this. it sounds like a good idea to try the seal first and see where that goes. the more i think about it i am convinced the next step is to do some crank stuffing. this stock set up has such a large crank volume it just cant create a very large pressure differential. it very well may be that there is not enough of a pressure differential created for atmospheric pressure to push the air into the induction sytem at a velocity to where a change in the reed valve restriction to flow would make a difference. Anyhow as far as moving the backplate inward on a 2 inch dia a small move should make a large reduction in volume so i dont think it will take much.

    I so agree with the ring but that may have to wait a while as i am now broke lol. darn swap meet. oh poor me i know lol. anyhow the rings are 12 apiece so he told me it was 24 for the 2 ring set up delivered.

    I am also wondering if i could set up two ports on the crankcase and use a one way valves one in and one out. I could use this set up along with a u tube manometer to measure the pressure differential created with a given port, valve and crankcase size configuration. this could be very interesting.

    Wow I hope i didnt miss anything lol.








  22. #147
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Ajonr and twin star i replied to both of you in my home e-mail. i then logged on to rcu and saw i had messages which were the same ones i replied to. when i reply from my home e-mail i am wondering if it goes to you or to rcu. did either of you get my reply if not let me know and i will get it to you again.

  23. #148

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Combatpilot-
    Didn't get anything from you.Go direct.
    aj0nr@sbcglobal.net

  24. #149
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I didn't get any thing either!
    No engine parts were deliberately harmed in this process.

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    OK. something started to bug me,so I got the digital mic out and started to measure everything again.
    I have 1 that is differant.The piston is 1.306 in. It came from the small case.It is 2.0615 in.inside diaganal from bolt to bolt.
    The other cases measure 2.1990 in. inside case bolt to bolt.

    There are differant cranks. Long and short shafts.I was able to compaire them with one I dropped and bent the shaft.That one was the larger case.
    by the measurements,there is no way the large case crank could fit in the small case.
    I have put some back together,swaping heads to cases.Some do hit at top dead center. Some don't.
    I have 5 differant heads also. 4 slots runners, 2slots, 2 slots with comp releifs, 2 slots that is just differant, and then the smaller cylindar.
    Now the question.Are they all 31cc ??
    The smaller cylindar is maybe 28 cc.


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