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

Ok there is so much fragmented information on the improvement of ryobi performance it makes my head spin. The descriptions of what was done to improve the performance are usually vague and leaves allot of questions. My intent of this thread is to discuss in detail the building of and hopping up my ryobi engine part by part piece by piece and how the improvements affect engine power one modification at a time so we can tell what works and what doesn’t. I intend to post pics of all the processes I go through and hope that others will post some pics of their engines and parts so we can all see some of the differences in the ryobi parts and what works best. There are so many differences in parts it is mind numbing as is seen in the ryobi differences posting.

Ok so here we go. This is my engine. I am not going to cover the conversion of these engines as there is already so much info on this process already. I am only interested in covering performance modifications in this post. My engine was purchased at harbor freight a few years back for 50 bucks. I wanted this engine cause it had the two rings set up. The first engine I had converted was off of a weed eater of unknown manufacture I had picked up out of the trash. I still have the parts and will use them for comparison in some parts. I had used some of the parts from the first engine to build the harbor freight engine. Mainly the carburetor back plate. The flywheel I had modified for the first engine would not fit on the harbor freight engine as the key ways were different. Also the harbor freight flywheel had the key cast into the wheel. Anyhow modifying this part is not that big of a job and I did it on a friends lathe.

Here is my engine in pretty much stock form with only the conversion modifications. It has the back plate off of the first engine as it was already modified and I didn’t want to take the time to modify the new one. You can see that this engine had the mounting cast on to the case and needed to be removed with a hack saw and cleaned up with a die grinder. It’s not too hard to do. The first engine you could unbolt the mount and did not need this modification. I actually like the cleaner look of this case as it cleans up nice and I’m sure weighs less.

Running this engine in this configuration the best it would do is 6450 rpm. This is with a Dynathrust 18-8 prop. All my conversion parts are from paragon aeronautics as I liked their set up the best.

http://c1.ac-images.myspacecdn.com/i...c0d6acebf0.jpg

As you can see I have the short shaft version.

http://c1.ac-images.myspacecdn.com/i...65c3131a70.jpg

With the engine all disassembled you can see when the keyway is straight up the rod journal is just slightly right of center. It would be nice to see some pics of others and see how this compares to others so we might get an understanding of the timing and interchangability of the stock ignition system. I plan on going electronic but that is at a later time.

http://c4.ac-images.myspacecdn.com/i...422b23aba7.jpg

My rod is a stamped type with a flat top piston. It looks to me like there is tons of room for a domed piston to up compression. Again post some comparisons on the rod and pistons please.

http://c4.ac-images.myspacecdn.com/i...a6b27b7ef7.jpg

Here is my exhaust port. It doesn’t have the middle bar and the rings are already pinned on the piston. I think there is room for improvement here as it seems kind of small.

http://c2.ac-images.myspacecdn.com/i...689bcfee51.jpg

Here is a view of my intake transfer ports. It is very interesting how different they are from the ones that were posted on the ryobi comparison thread. Notice how they have a piece in the middle of the port. I think there is lots of room here for improvement but in a way I hate to grind any out of this as it will lower low end compression. It may be worth it in gains of flow. It would be interesting to see if they have the same volume as the ones that do not have this middle piece. I don’t know why they did this other than to de tune it to meet EPA regs. Again let’s see some pics for comparison.

I will at a later time degree this out and figure out what the port timing is.

http://c2.ac-images.myspacecdn.com/i...6e0fed77a5.jpg

Here is my back plate. It is stock other than being cut down. I did bend the reed valve stop out to 1/8" as I read somewhere this was the thing to do.

http://c1.ac-images.myspacecdn.com/i...06dc2ddbd4.jpg
On closer inspection of my back plate I made what I consider to be two important discoveries. The first being that this back plate off of the first engine is of a smaller diameter than the harbor freight engine. This allows for a loose fit and increase in the low end volume which is bad. It looks like the same difference in diameters that avi8to77 discovered in the differences 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.

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

It would be really cool to see a "before and after" comparison of using a Frank Bowman ring. The Ryobi has a large ring gap because the ring does not overlap the pin in any way. With the Frank Bowman ring, you either tap the pin halfway down into the ring land, or grind it half way down. Then Frank's ring has a notch that fits over the pin, allowing a MUCH smaller ring gap, which helps power a lot. I suspect the benefit would be slightly less on a two ring piston than on a one ring, but there still would be a benefit.

I just don't have the time and patience to do a one change at a time, comparison test program. This will be interesting.

AV8TOR

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

I think thats a great idea. Do you have a link where to get these rings? How much do they cost. Cost is knind of an issue right now as i havent worked much lattley. Stupid economy and housing slow down. Right now I have more time than money lol.
Jeremy

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

He doesn't have a website. His contact info is:


Frank Bowman
Email: [email protected]

Phone
Home: 505-327-0696

Address: 1211 N Allen Ave
Farmington,, NM 87401

The rings run about 12 bucks shipped.

AV8TOR

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

I am going to have to keep an eye on this thread. I have a ryobi which is ready for testing. I went ahead and ground the transfer ports, so they are one big slot instead of 2. I posted this a while ago, and i think the title was: could this be the key to power. I havent ran the engine yet cause i dont have a mount. I should also look into getting a tach so i dont over rev the engine. If i ruin this engine, im not too worried, i have a nice stihl engine waiting to be ran as well.

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

I was looking at doing the same thing. I am wondering if they did it this. I would really like to see what this does. By chance do you have any performance specs before this mod so you have a comparison?

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

no unfortunately i dont... i dont have a tach, so no numbers. What i could do is get another jug and bolt it on when i get my tach. I was really wanting to see if this mod will even hold up, cause im afraid that the ring doesnt have enough support. I really need to get a mount for this thing. Do you think that making a mount kinda like a glow engine will work? and have it bolted onto the jug. or should i make stand offs. I dont want to use a plate mount, cause i dont have a carb spacer so the throttle will open all the way.

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

I dont understand the question. This engine dosent have mounting lugs like a regular glow engine has. so then from there you would either have to weld on lugs or fabricate some sort of mount that would bolt to the engine to accomplish this. Where would you attach this mount? the engine that I have dosent have the flywheel shroud mounting lugs on it. I suppose if you have these lugs on your engine as I know many of them do then I dont see why you cant fabricate a mount to mount off of the front of this engine and would have lugs like a regulat glow engine. That being said it seems to me it would be far more easy to fabricate a carb spacer out of a flat piece of aluminum, than it would be to fabricate this elaborite mount. i dont know that mounting it off of the cylinder holddown bolts would work well or not. the thing that would scare me about that method is the fact that there is only two bolts to work with and very small area to bolt to. it may be possible that with only one bolt per side the vibration would be hard to control to where it would not flex the mount and cause it to crack from work hardening. I will have to stare at my parts for a bit to ponder this.

If you get a tach i would recomend the glowbee tach. I really do like mine.

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

i have been pondering for a while now. lol... i just wanted to do this, cause i can get the mount that uses the jug bolts made for real cheap. Im not sure if this engine will even make it to a plane, i just want to be able to run this engine on a test stand for a couple hours. but if its going to crack the jug where it will be bolted on, then i wont risk it

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

If all you want to do is run the engine on a test stand then how hard would it be to fabricate a mount that utilizes the front mounting holes? it could be a really simple piece of angle iron.

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

I guess i could probably think something up. Im heading home today, so when im at the old man's shop, i could probably "borrow" some materials, and make something up. Once that is done, I will just need to make a battery pack to make an onboard glow setup. I am going to try and run the engine on gasoline with a glow plug powered all the time. Rysium has done this, with good results, so im going to try it.

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

[img][/img]I got a chance to get by the shop and get all the parts from the first older engine I converted. Here is the comparison of all the parts

to start with the flywheels are made by two diffrent companies. the old one by phelan and the newer one by walbro. For all intensive porposes they are esentially the same part. the only noticible difference is the keyway size. the newer on has the key cast into it eliminating the need for a key. You can see by the tip of the pen there is a little bump that indicates the location of the keyway. you can see that the keyway is in the same spot on both of these flywheel in relation to the magnet casting hump. this is important to note to see something in a later pic.

http://c2.ac-images.myspacecdn.com/i...0e44c99951.jpg

the next pic is of the pistons. the newer one has two rings and has a different rod than the older one. other than that they are pretty much the same. same rod length same bearings same piston overal dimensions.

http://c3.ac-images.myspacecdn.com/i...a359316162.jpg

the next pic is the cylinders. there is a bunch of differenc in these. first off the transfer ports are altogether different. the older one has the single port per side and the newer one has the two smaller ports per side. I really dont know why they went to the two ports per side version. it looks like the ports when all totalled together have the same volume per side. My only guess is that this configuration will deliver the fuel and ait mix into the cylinder with more velocity and speaed it out a little better in the cylinder.

the next is the exshaust port. the older cylinder has the center bar and newer one dosent. the older cylinder port exits straight out. the newer cylinder the port sweeps up just alittle and flares out twords the end as it exits the cylinder. it also looks like the port timming is different but i havent had a chance to confirm this.

The last difference that i can see is in the combustion chamber. if you look at the chamber where it forms a lip as it transitions into the cylinder the older cylinder has a wider lip than the newer one. this wider lip makes it look like the dome to creat the combustion chamber is smaller. It is my oppinion that the older cylinder is a higher compression cylinder. I am trying to think about cc ing the combustion chamber to find out what the differenc in combustion chamber size is. I would also like to get compression ratios on these engines. I am wondering if I put an oring on the single grove piston if I can get a seal where i can cc it that way.

http://c1.ac-images.myspacecdn.com/i...6a3ce862ac.jpg

here is a pic of the exhaust ports. it is kind of hard to see the differences in these pics.

http://c3.ac-images.myspacecdn.com/i...6aea562b1a.jpg

The last and i think the most importtant is the difference in the timming with the stock ignition. We already know that the flywheels are pretty much the same. If you notice in the pics the cranks are turned to where the keyways are straight up. the newer enginge the rod journal is almost straight up or a little to the left. the rod journal in the older engine has the rod jornal noticaby visible to the right. this would advance the timming of this engine when using a stock ignition. again we already know the flywheels are the same soit has to be advanced. The cranks look to be the same other than the keyway. since i already have a flywheel for both cranks I intend to install the old crank in the new engine and see how it affects power on one of my tests. again this wont mean anything if you use an aftermarket electronic ignition but i want to do it so the guys using stock ones will know.

http://c1.ac-images.myspacecdn.com/i...d007b0ea30.jpg

There is a huge difference in compression between the cyingle ring and the dual ring when pushed into the cylinder and your fing held over the plug hole. the dual ring one darn near cant be puished in unles you give it a little time to let the compression leak out. The single ring one can be pushed in easily. I dont know if it will do any good to test the old engine with the original piston and ring. I think however it would be worth a look with the new piston and ring setup in the old engine. this shoud give me a good idea of the performance charateristics between the cylinders in stock form.

I also miss spoke on the back plates. as far as i can tell the case sizes are the same and the backplates are the same. the backplate just has a sloppy fit.

So again from here I am gona fix my reed valve problem and re test to get a good starting point.

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

Swap meet/Ebay time.
Evra 190 was sold by Hobby Lobby for a few years. Its a Ryobi 31 with mounting rails cast in to the crankcase.

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

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

I took apart a couple of Ryobis that I had last night. One of them has the smaller crankcase with the recessed reed in the backplate. It looks almost brand new. The other one was a little dirtier but has the larger crankcase with the standard backplate. It also has the cylinder with the slits cut up from the exhaust port. Both are long shaft engines. Both have a single piston ring. Both pistons appear to be identical. So I thought I would use the like new piston and cylinder off the small crankcase motor and mount them on the standard crankcase. Once mounted up, I discovered that the connecting rods are of different lengths. The piston from the smaller crankcase hits the crank before reaching bottom. I wonder if I will get a good engine if I use just the cylinder from the smaller crancase mounted on the larger crankcase with the piston and rod from the larger crankcase. I forgot to compare the transfer ports. What do you guys think?

Jim

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

did you install the piston 180* out? the piston skirt is higher on one side than the other to keep it off of the crank counterweight...

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

Thats a very good point on the pistons.. can you switch the pistons on the rods? I am thinking the smaller crankcase may be a better engine if you can get one of the new style backplates to fit it. I dont have a recessed backplate so i cant compare. If the recessesed backplate and smaller crankcase has a smaller crankcase volume it mat be the better choice. What does the timming look like on these engines? it would be interesting to see.

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

I did have the piston turned the right way. Still hits the crank. There is no way I can see to put the good backplate on the smaller crankcase. It is just too small. Keep in mind that the crankshaft on the smaller crankcase has a shorter off set therefore the connecting rod has to be longer. Just wondering how this will affect the stroke and compression when swapping the head to a standard crank and connecting rod.

Jim

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

I think it stands to reason that the engine with the bigger crankcase is gona have a longer stroke. so if the stroke is longer and the bore dia is the same on both engines than the engine with the longer stroke is gona have more displacement. there is two truths i have found over the years when it comes to engines

1. There is no replacement for displacement

2. Cubic inches cost cubic dollars.

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

the one with the shorter stroke was probably the 28cc. whereas most of the ones that u will see are the 31.

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

Long ag and far away Ryobi made 26cc engines. I may still have one laying around I compare it to the pictures and a 31cc we got.

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

The one with the smaller crankcase did look like an older engine. It had one of the round mufflers on it. It also was the one that was the cleanest looking. If it is a 28cc, will the cylinder work on one of the 31cc crankcases and piston rod assemblies?

Jim

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

It should work, cause it think the bores are the same size. U should probably measure to be sure, and do a mock up assembly and make sure everything works properly.

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

Tommorow or maybee monday I should get to do some testing. I think this is gona be my test procedures.

Test #1 Stock engine no performance mods. Using old engine 1 ring piston and new cylinder. record RPM I really want to see the rpm diff in the 1 vs 2 rings. I have a brand new ring for the one ring piston.

Test #2 Stock engine no performance mods. New 2 ring piston and new cylinder. Record RPM. This should give a good comparisoin between the two rings set ups.

Test #3 Stock engine no performance mods. New 2 ring piston and older one ring cylinder with higher compression and different ports. Record RPM

Test #4 Best of 1-3 and no cylinder base gasket to up compression. Record RPM. Should change port timming but no port mods at this time.

Test #5 Best of 1-4 and check port timming and modify if necassary. Record RPM

Test #6 Best of 1-5 and old crank from older engine with advanced ignition timming. Record RPM

Test #7 Best of 1-6 and new 12.8 mm venturi carburetor. Record RPM

Test #8 Best of 1-7 and moddified reed valve. Record RPM moddification will be discussed later. mostly reprofile valve and thinner reed stock.

Test #9 Best of 1-8 and rework the manifold and bell shape it at the reed valve end to reduce contact surface area. Record RPM

Test # 10 Best of 1-9 and and try to reduce crank case volume. Record RPM

Test # 11 Best of 1-10 and use electronic ignition. Record RPM

If have money and time I may try to make the y manifold

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

oh pretty please could u get some video? :D

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

It is great to see all the other info about the Ryobi.I have torn apart about 20 of them and found alot of differances with them. 1 the lower part with the crank,two differant sizes,some of them have been milled in production and some are cast and cleaned up, also the front seal/bearings are differant on some of them.The outside case,some are wider than others.2The heads,the newer Ryobi's with the "E-Z start "in the title are the ones with the compresion vents that go up the sides for emisions complience.I could go on and on,BUT I have found an older engine that was dated 1978 that had 2 rings on the piston and the rod was forged aluminum and held to the crank with a bolt( name was 'Piston Powered Products model # 99).The other one I have is a Troy built/MDT dated 3/2006 also has two rings on the piston,But this is the new casting I have heard about .The lower crank case has the magneto shield as part of the casting.This will require much more work to convert.

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

Sorry I dont have video capabillities. Didnt get a chance today as i had to work on other things. responsibility suks. Maybee tommorow.

What was front bearie difference you have seen on the crank seals. What I have seen is on my older engine the seal was after the inner bearing which leaves no way what so ever to lube the front bearing. the latter model has the crank seal out at the end of the shaft next to the flywheel. This allows for good lubrication of the front breaing but it also inscreases the crank case volume which is undesireable. this is a trade off either way. I think i will put the seal next to the inner bearing and use some grease in the outer bearing and see how this changes performance. I will do this in the reducing crank case volume section of the test.

If you look at the pictures you will see that my newer engine had the cast on mag sheild. You can see how i cleaned up mine and it really looks quite nice.

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

I was able to see the differance in the front seal after I dropped one.oops.It was a long shaft with the seal on the front then bearring.I could see a 1/4- 3/8 " space in there.I have 7 short shafts with the seal first and only one that has the bearring first.Long shafts ,4 with seal first and 6 with bearing first.Some of the motors were Ryan or other type,and the rest are Ryobi.2 large bearrings one far forward and one aft next to the rod/counter weight.

What is everybody doing to replace the mag space when you put on the EI conversion??

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

I was told that you leave the mag off. I jusst dont see how this will work with the paragon prop hub that i have. I plan on putting my flywheel in a lathe and turning it down to the size that i need. I should be able to acomplish this by removing the crank and putting the flywheel on the crank. then using the prop hub adapter to chuck to to center it all up right. Its gona be a while before I can do this though as i just dont hacve the money. work has suked lattley and i have a lot of chatch up to do

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

It sounds like you have a prop hub for use on a magneto equipped engine. It just takes the place of the nut that holds the magneto on. I have used these before. What you can do is take a hole saw, and carefully cut the center of the magneto out, as large as is practically possible. Then dress it round, preferably with a lathe. You can then use it to "adapt" your prop hub to the crank. Just place the magneto center you made onto the crankshaft, and then screw on your prop hub. If running Gas/Glow, that's all there is to it. If running electronic ignition, then drill either the center piece you made, or the prop hub itself for a magnet to trigger the sensor.

Of course, if you are going to run the magneto ignition, then you must use the mag flywheel. Some people cut off the fins to reduce weight and eliminate the power robbing drag of the impeller blades. Rebalance the flywheel afterwards if you do this.

AV8TOR

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

Av8tor1977 thats pretty much it in a nutshell. Thats pretty muck what i figured on doing only i was just gona cut it down in a lathe. Any idea where to get the magnet and the shape, size and type?


I got a chance to do some testing today. I think my results are pretty interesting.

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
conclude this. Since there is a difference in the interchange of these part i now feel there is some timming in the coil assemblies themselves. I am not sure how this is accomplised but i am sure it is something electronic. I would like to check the timming but i need to make a degree wheel and fixture for a dial indicator to find TDC. Once this is located i can then make a TDC timming mark on the flywheel and somewhere on the case for a reference. using my timminig light i can tune the light till the timming lines up at TDC. then all i have to do is look at where the knob on the timming light is and I will have my advance number. I will have to check this when I get time. If I can get an electronic ignition all this info wont even matter but it is still worth doing as i hope guys using the stock ignigtion can gain from this information.

Next I will move on to the larger carburetor. I need to do some modifications to the carb so it will fit this application. The carburetor I purchased is a walbro #387. It has a 12.8 mm venturi. The modification i need to make is: Change the throttle shaft as the old shaft has a better arm to it. The fuel pump cover needs to be changed also as it has the correct idle adjustment for this arm. other than that the only other thing that needs to be done is to remove the throttle return spring. I will proceded with this when i get more time.

All in all i have so far achieved a Gross gain in rpm of 370 RPM

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

You have lots of patience. Thanks for posting the results. Classically, the best "weedie" performance gains are from a more free breathing exhaust, and from a larger carb. One won't work well without the other though; with the more open exhaust having an advantage if you are only going to change one thing usually. The next thing is to check the exhaust port timing. Some Ryobis have a really low exhaust timing of around 120 degrees. Bringing them up to about 150 really livens things up.

A good way to check your deck height without all the caliper work is to use a piece of solder. Bend a piece so that when inserted into the spark plug hole, it touches the side of the cylinder. Then turn the engine over a few times. The piston will smash the solder against the head, and then you can measure it for your "deck" or piston/head clearance. .015" is a minimum deck height, with maybe .020" being a bit safer or a good idea for high rpm engines.

AV8TOR

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

Oh, and what prop are you using in your tests?

Also be aware that changes in temperature, and to a lesser extent, barometric pressure and humidity will affect your results from test to test when things are close.

AV8TOR

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

Yea i know that will all effect it. and it will change from day to day. Unfortunatly i have no control of this. all the test so far were done in a 4 hour period and so the weather conditions should be pretty close.

I am using an 18-8 prop.

I do plan on checking the port timming i think i have that in test #11

As far as checking the deck height it really isnt that hard to do it with the calliper.

You got to admit it is pretty interesting that the older cylinder is the better performer. I had a suspicion this would be the case as it does have a higher compression ratio.

I dont know if my muffler is beter breating or not. i have never tried a stock one and the one i have now it the paragon muffler. it has two giant outlets. Some back pressure is desireable in 2 strokes though. it is possible to go to far and reduce performance.

Even with only 370 rpm gain the power output gain is pretty noticeable.

At this point i am inclined to say find an older engine with the single intake runner per side and the higher compression ratio and add a two ring piston to it. the two intake runners per side may be just fine but this cylinder has a much lower compression ratio.

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

Ya know something that keeps bugging me about this engine is everyone says what a weak rod it has. Has anyone acctually seen one of these rods fail? I dont know why you cant run it like a regular aircraft engine where you only use the full power at take off or when doing a manuver and reduce the power at cruise. Regular aircraft engines wont take or not supposed to have full power applied for long periods either.

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

Yeah, I have heard of a number of them blowing up, but only when pushed well past the recommended static rpms of 7500.

Throttle back? What's that? Well, I use the throttle stick, but many of the flyers I see fly just push that stick all the way up and leave it there.... (My brother is one of them.) ;)

AV8TOR

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

actually one of the guys that taught me to fly told me not to worry too much about throttle. The other guy that taught me stressed it alot. It actually helps alot when flying. I think that people who use the throttle, even if its just a little bit, make better flyers. I usually like the ratchet on my throttle stick to be very loose.
Well, to get more on topic, were supposed to have nice weather (nice for being outside not for flying) so i might get energetic and finish my mount, so i can test my ryobi. Like i said before, i dont have a tach, so wont have any numbers. I just want to see if the engine will run and last with the area between the transfers removed.

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

I had some more time today so I performed test #6

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 !!!!!!!!!!!!!!

Ok so far just using the best stock parts from different engines and a 12.8 mm carb venturi from ebay with no special mods other than a thinner base gasket I have acchieved a gross RPM gain of 870 RPM !!!!!!!!

I was a bit dissiponted in the flywheel and crank swap. I was sure this was going to yeid some increase from advanced timming. This just was not the case due to the fact that I am thin king the timming is set within the ignition coil electronics as the coils could not be interchange with the other flywheels.

I am debating weither to do the electronic ignition first or do the backplate mods first. I probably will do the backplate first as i dont have any money to but the ignigtion yet.

It would be nice to see someone follow the same process I am doing to see if they get simmilar results. All in all I think we are starting to see a map of what changes or mods will yield what gains in power.

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

you can still advance the timing with the stock flywheel, remove the key from the crank and put a little loctite on the taper, that should hold it in place

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

Here is my take on the prop hub issue. All I need now is the Hobbyking CDI unit w/hall pickup and a magnet.