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

TKG i cant agree with that more. If your unsure of the order of the parts refer to this site

http://web.archive.org/web/200501161...ro/family2.asp

Select your carb and there will be a parts diagram expanded view.

Ok here is some info straight from the FAA Airframe and Powerplant Mechanics Handbook. EA-AC-65-12A

Notice there is no mention of vacume and there is talk of pressure differential.

The only difference of this carb and a walbro is the diaphram seperating the fuel and atmosheric air and diaphram position opens and closes the needle which is the same as fuel bowl level opening or closing it. by the way add a diapram to this carb like a walbro and now you have an inverted flight negative g carb.

I spent 13,000 to learn this in 94 and now I give it to you for free

Sorry about the cropping as its the only way I could get it to load readable size.

http://c1.ac-images.myspacecdn.com/i...cd51ad413c.jpg

http://c3.ac-images.myspacecdn.com/i...7e083e3876.jpg

http://c3.ac-images.myspacecdn.com/i...bb7edd7c36.jpg

http://c3.ac-images.myspacecdn.com/i...47ada538d2.jpg

http://c3.ac-images.myspacecdn.com/i...ac6d57c736.jpg

http://c3.ac-images.myspacecdn.com/i...c68c4c2e52.jpg

http://c1.ac-images.myspacecdn.com/i...7e46a3821c.jpg

http://c2.ac-images.myspacecdn.com/i...a372d5a585.jpg

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

I've read the link, combat, many times in fact. I have the page saved in my favorites. I have tried the float lever at several different heights, and nothing changes. But I will try again. I have also double checked the orientation of the gaskets and films on both the pump and the diaphragm side, and all is well. I have also started another thread on the topic so as not to detract from your testing. By the way, this is a Zama carb, did I mention that?

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

I hope you got some lube with that 13 large! I paid $900 for my A&P.

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

Where in the world did you get a&p training for 900. I went to colorado aero tech. I stand by my decicion there as the training was excellent. the fact you cant understand how a carb works tells me maybee you got what you paid for.

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

from what your saying now I would be willing to bet your needle valve isnt shutting the fuel flow off for whatever reason.

I havent had a chance to look at a zama carb but i bet its not much different

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

Ouch. I went to Parks for AvSvcience, then went to work for Garrett for about 6 years and accumulated the necessary time for the FAA signoff. Then I went to Browns' in Okla City for the test prep, test and o's and p's. It's not that I can't understand, I just don't study the particular subject in any great detail when there are so many others willing to share what they know about the subject.

Anyhow, I tried the lever at level to the carb body, just below, and just above, earlier today. I did notice that the needle didn't seem to move much, if at all while pressing down on the lever against the spring pressure when it was at level and above. Perhaps I didn't get all the gunk out.

Good luck on the testing, I hope all goes well. Nice looking test bed, too.

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

again like i said on the other post

Racin im not trying to beat you up. sorry if you feel that way and sorry if i offended somehow. Lets agree to not let this go any further. I am sure we are two intelligent highly skilled people so lets put our heads together and solve this.

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

Ok I got my new test stand done today and here it with engine running on it.

http://c3.ac-images.myspacecdn.com/i...a4a8d28ed2.jpg

http://c3.ac-images.myspacecdn.com/i...c266b27b0a.jpg

http://c1.ac-images.myspacecdn.com/i...a62de80090.jpg

I tried to test the exhaust timming mod today to. the best i could get was 7380 rpm which is down from the 7440 that I had been getting.

I had a static thrust of 13lbs 10 oz.

I dont know how acurate all this is as i discovered some problems.

1st my engine would not hold a steady top end rpm. it kept kind of searching and you could hear it do it to.

2nd I dont know how accurate my tach is after droping and repairing it. I have one of them laser tachs on the way to check against.
I am of the opinion that these hobby tachs suk pretty bad and are very general and not very accurate at all.

3rd I could not get a steady idle and it changes every time i run it. I discovered here that when i chenged the throttle shaft out from the old carb it lets it vibrate around and wear some slots into the edge of the butterfly valve. as you can imagine the larger they get the worse the idle. now i know why it changes ever time i run it also.

4th when i was dissasembling my engine again i discovered my spark plug was loose. what can i say but DUHHH!!!

I need to get thses four things ironed out before I am willing to make a good determination on the exhaust timming change test.


Ok also when looking at my rings it has spots in it that are shinney and other spots that are not and have a good coat of varnish on them. It seems to me if the rings are contacting all the way around the ring face should be shiney all the way around where it is in good contact with the cylinder wall.

This really makes me wonder how good of a seal i have with this ring cylinder combo.

Aviator1977 said it well in another post that this is a very basic important starting point. Its got me thinking on how do we figure how good a seal we are getting? I then remebered my airplane training and i havent had to do this for years but i think we could build some leakdown testers and check it that way. If you are unfamiliar with a leakdown test i will have this procedure later and we can all know where e are at cylinder seal wise. you can see how it works here to http://en.wikipedia.org/wiki/Leak-down_tester

At this point I have what i feel to be to many inconsistencies in the testing procedure that I am contemplating stopping this thread and starting all over on a new one. I guess the best way to look at this thread is it was a good education on getting a good consistent testing set up. I also need to purchase a new carburetor to. I think i will get a couplke just to have some on hand to.

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

combatpilot,

I guess I don't understand why you want to close this thread and start a new one. I would be inclined, if I might give my $.02, to forge ahead with the original topic of the thread and that is ".....ryobi performance modification, analysis and comparison". There already has been a wealth of information collected about what works, what doesn't work, and what might work in the quest to get more out of the Ryobi. Part of the process of discovering what works to improve performance IS the "guess/try/guess again" nature of the work. Just because you've hit some snags doesn't mean you should give up! If you started a new thread it would just create a discontinuity on the subject. Although I haven't done a thorough search on the Ryobi subject I'd bet this thread is one of the longest yet, even though there are only a handfull of contributors so far. It's true that there are a number of off topic posts, which is to be expected, but sometimes those posts spark some interest in other areas that are related to the subject.

If you started a new thread on the same subject what would you call it and how would you relate it to the information that has been collected on this thread?

diceco

BTW I've just completed an analysis, using Gordon Jennings two stroke tuning book, and discovered that for the bifurcated transfer port cylinder, the transfer ports are plenty big enough to give peak power at 7500 rpm but the exhaust port is not. I further determined that the duration number of 150 deg for the exhaust port, that's been mentioned by several, is just right if obtained by raising the top of the port 0.11 inches. This not only gives greater duration but larger area also. In so doing Jennings suggests an elipsoidal shaped port and proper radiusing and chamferring of the edges of the port. I'm looking forward to see what the performance gain really is. Even if one doesn't use the calculations in the book, his general comments on what makes two stroke motors work is very good reading.

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

Yeah, I really like that Jennings book. Good info.

Really nice job on the test stand Combat Pilot.

AV8TOR

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

Well the thought is that i dont know how accurate all my information so far is as i have had large problems in my testing procedures. As far as I know this is the only post that I have ever seen that has this kind of information on ryobis. I think regardless weather I start a new thread or continue on this one I need to startf rom the begining again when i get my testing procedure worked out better.

I really do need to get my hands on that book.
My library dosent have it does anyone know where to get it?

Ok here is the perfect reason why i started this post.

http://www.rcuniverse.com/forum/m_8616877/tm.htm

7500 on a 18-6 prop and absolutly no information on the setup. taken from a troybuilt but no info in the cylinder it uses. I know im using an 18-8 but i just cant see that making that much difference. I just dont understand how hes getting to 7500 when i cant get past 7400 with all ive done so far?

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

i think that u should continue this thread until we get a final setup thats proven to make power. When that is complete, maybe a thread called "proven mods for a ryobi" would be in order, with only proven mods stated. In canada, we have just got a foot of snow, so i cant really get out and test my engine again. I would really like to get rpm numbers, but its too cold for my tach to work.

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

It's on the Net here [link]http://www.edj.net/2stroke/jennings/[/link]

You bet it makes a difference in prop speed, a BIG difference. See post #195. jester241 said he's using and 18x6W prop. It sure looks like it's an APC prop! If it is then his motor would turn about 7000 rpm on an APC 18x8W prop.

diceco

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

Pitch can make a pretty big difference on static rpms. This is because when a higher pitch prop is not moving through the air, a good portion of the blade is stalled and causing a ton of drag. This is also why lower pitch props are used for 3D flying, as lower pitches are more efficient at lower, or zero, airspeeds. As an aside, this is also why high performance full size airplanes use variable pitch props.

I keep telling you guys, a Frank Bowman ring is the first mod to do after you have a free flowing muffler and an 11mm carb on a Ryobi. The second thing to do is raise the exhaust timing to 150 degrees.

Take a good used cylinder, sand it carefully with 400 to 600 grit sandpaper, and put a Frank Bowman ring in it. If your engine isn't sealing well, all the mods in the world won't help as they should. It is just basic good hot rod practice to overhaul a used engine before modifying it. Bearings, seals, and ring should be perfect first, then start modifying. An aftermarket muffler costs 30 to 40 bucks, a carb retails for around 40 bucks, an ignition system is 80 bucks plus, a lowly prop is at least 15 bucks. A Bowman ring at $12.00 shipped is a cheap investment, and they flat work.....

Once again, I have many times seen engines with moderately worn stock rings gain 600 to 800 rpms with a Bowman ring. The recommended ring gap for engines of these sizes is around .003", and I'm betting all of yours are significantly more than that.

AV8TOR

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

I don't think, at the prop speeds and pitches we are considering here, we have a problem with cavitation at static conditions. Cavitation unloads the power system. Sure the drag of the prop increase in those areas that are cavitated but the fact that there is no lift in those sections causes a net decrease in the power system load.

If we went to an 8in pitch prop from a 6in pitch prop, from the same manufacturer and model prop, and saw no decrease or if we saw an increase in prop speed one might suspect some cavitation. But based on my back to back test of the APC 18x6W and 18x8W props the results are as expected. You move more air at the higher pitch, it loads the power system down and there is a decrease in prop speed.

diceco

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

Diceco thanks for the link. On the prop issue i guess thats why is so important to have a test standard prop that is tha same manufacturer dia and pitch for all our test information.

Aviator I cannot disagree with any of that and I think i have been underplaying the importance of a good seal. I think on my engine that when it warms up it is losing seal for whatever reason. when run to full throttle it runs out good then slowly losses about 180-200 rpm as it gets hotter. if reduced to idle then let cool for a bit and run back up to full throttle it has the same results. This is part of why its so hard to get a good consistent reading and why i say my testing is somewhat flawed.

I made a leakdown tester yesterday. I could not air it up to 100 psi as my buddies shop i made it at didnt have air that went that high. he best i could do is 80 psi.. When I built it i had made a orfice with a .040 dia. when used on my engine with the prop at TDC and held there i got a reading of 78/80 psi. That means the input pressure was 80 psi and the pressure in the cylinder aft of the orfice was 78 psi. this can be expressed as a percentage of leakage but I need to figure out the math. When run at 100 psi the math is easy lol. 1 psi - 1 %.

I didnt think this had a good enough resolution so I wanted a smaller orfice. the best i could do was .023 as I had to use a tip out of a wire feed elder for the orfice. smallest drill bit I had was .040. when this tester was run at 80 psi i got a reading or 76/80. This is a little better resolution. I would really like a .010 orfice. I think even as this dosent seem like much leakage and in a 350 chevy it wouldnt be but on this small of an engine its a bunch. I removed the carb and held the reed valve open when this test was performed as my thought was that if i didnt with the reed valve an leakdown wouldn have a place to go like in a crankcase on a four stroke engine. You could hear quite a bit of leakage. If you rotated the prop the seal was best at the tdc and was pretty lousy at ather spots int he stroke.

I will get some pictures of this on later and will keep working on this so we can get an acceptable range for testing standard purposes. this should help give more consistent information from all of us if.

I would really like to see what kind of a reading av8to1977 is getting on his as his seems to be the best as far as seal improvements so far.

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

I am starting to think rather than starting a new thread im gona do another engine conversion side by side with what I already have for comparison to see if my results are the same between the two and I can get a direct comparison that way.

Here is the info on the leakdown testor.

Here is a bunch of stuff I already had on hand with the exception of one brass nipple, one pressure gauge and one air coupler.

http://c1.ac-images.myspacecdn.com/i...c94046a2d4.jpg

I took and machined a aluminum slug that would lightly press into the pipe nipple that goes between the gauges. it has a .040 hole in the center and it is .500 inches long. this is What makes this tester work and if we all post results on here from one of these testors it needs to have this same dia and lenght orfice or it will be different results.

http://c1.ac-images.myspacecdn.com/i...a033667234.jpg

I used the vice to press it into the end of the brass nipple and the tapped it a little further into the nipple

http://c4.ac-images.myspacecdn.com/i...81c33688d7.jpg

http://c3.ac-images.myspacecdn.com/i...78e5ce4f26.jpg

It wa s all put together and here is the final result. the hose that screws onto the plug hole is off of a automotive compresion tester I already had and this makes it ieasy to use. the schrader valve has to be removed from the end as the valve will not let the air travel in the direction we need. It just happened to have the quickchange type of end tha matched one that was cheap at harbor frieght.

http://c3.ac-images.myspacecdn.com/i...38e8f9c71e.jpg

I left the schrader valve in the hose and pressured it up and as you can see my gauges are pretty even as this is crucial also that they be even.

http://c2.ac-images.myspacecdn.com/i...5645dbc4ed.jpg

Ok again the .040 orfice didnt have the resolution i wanted so i diassembled the orfice tube and pushed the slug to the end of the tube. i then drilled it out and tapped it to recieve the .023 welding tip. it was then shoved back down into the tube and reassembled

http://c2.ac-images.myspacecdn.com/i...cfa0045779.jpg

http://c4.ac-images.myspacecdn.com/i...914609999f.jpg

Ok now with it puged in and hooked to the cylinder the prop was held at tdc and you can see i am getting 76 psi after the orfice with an input pressure of 80 psi. without the orfice the pressure will be equal to the input pressure gauge as there will be no restriction to cause a pressure drop. the smaller the orfice the better resolution of pressure drop we would have but this is the smallest hole i can figure out how to get. The idea here is as the cylinder leaks the air pressure off and due to the orfice the input pressure cant get air into and past the orfice fast enough to equalize the pressure. the lesser pressure is our loss and can be expressed in a percent. again this is easy if the input pressure is 100 psi and i will try that when i can. the goal is to make the ring and cylinder seal to where there is as little of a loss in pressure as possible ie if my reading was 79 over 80 psi then that would be less loss that 76 psi over 80.

http://c4.ac-images.myspacecdn.com/i...86cbb5fe93.jpg

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

I think I have an 18 x 8 Top Flite or Zinger prop around here some where. When I get time, I'll get the Tiger Moth out and change the 18 x 6 on it for an 18 x 8 and see what it turns. Does 8500 on the Top Flite Power Point 18 x 6. I was pleasantly surprised that it ran that well, and checked it several times with my TNC tach. I know the TNC is accurate, as I checked it against a calibrated full size aircraft tach and it was within 1 (one) rpm of being in perfect agreement.

AV8TOR

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

I put the Ryobi back together after re-working the exhaust port and ran it up. It gained 255 rpm prop speed and 1.0 lb thrust; a significant amount to be sure! In the current condition the APC 18x8W turns 7630rpm and it pulls 15.0lbs thrust. These numbers are corrected to 59 deg F ambient temperature and 29.9 in Hg barometric pressure. The raw numbers, for those of you who don't believe in normalized data, were 7600rpm and 15.2lbs thrust. These were obtained by averaging three data points taken within about 3 minutes of each other.

The attachment shows a drawing of the exhaust port measurements; stock, objective (150 deg duration), and actual (160 deg). Unfortunately the port ended up being larger than I intended. A hand file is NOT a precision machining tool, at least in my hands!

A note of caution about porting the Ryobi. Gordon Jennings recommends cutting a shallow ramp leading away from the edge of the port, the purpose of which is to guide the piston ring(s) back into the cylinder wall from the bulging condition that a wide port might cause. I am certain he is speaking of doing this in an iron cylinder liner This should not be attempted on the Ryobi because of it's AC (aluminum chrome) construction. The chrome lining is very thin and no attempt should be made to cut a "ramp" in it. One should be sure there are no sharp edges in the chrome lining at the port lip, and do create an ellipsoidal port shape as suggested by Jennings. The bottom of the stock port is pretty much straight across. I very slightly cut the bottom of the port to make a slight curve in it's edge but this was only for the benefit of getting the ring(s) back into the cylinder for the last bit of travel before BDC. This will do nothing to the effective port area because the piston doesn't go below the bottom of the stock port at BDC. The slight cut to the bottom of the exhaust port is not shown in the drawing.


I also measured the cylinder head volume and found it to be 2.5cc. I then added the deck height 0.12cm and used the bore 3.5cm and stroke 3.25cm to calculate a compression ratio of about 9.5:1. Better than I thought it might be after hearing so often of those "low compression" weedie motors! Yeah it would be nice to raise the CR and get more torque but there is no practical way I can think of to do this. First off, the deck would have to be machined, then the cylinder base, but now you've messed up the port timing, so they would have to be reworked! Not worth the effort IMHO.

And one last test: After running up the motor on the APC 18x8W I switched to the Master Airscrew 18x8 Classic and got 260rpm more prop speed but 1.2lbs LESS thrust. NOT ALL PROPS MARKED WITH THE SAME DIAMETER AND PITCH PERFORM THE SAME!!

When I get a chance I intend to go back in my records and track the performance history and modifications of this motor from new-cut-out-of-weed-wacker configuration to the current configuration, which is about as far as I think I can go with this motor. The only other thing I might try is a free-er flowing exhaust system.

diceco

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

Pretty nice numbers. I only get 7360 rpm with a Top Flight 18X6 Power Point prop. Only mod is a larger bore carb. I'm using a Walbro WT-324 which is 11.1mm. I did open up the inside of the stock muffler some and put a 1/2" outlet on it. I've never had the cylinder off it so I don't know how the ports are in it. I would say it is one of the newer style low emission type engines so I may not get much more from it. What is the best gap for the spark plug when using EI? I've got mine about .020" gap. Any thoughts how to get a little more power out of this thing. I may need to get a new ring(s) from Frank Bowman. I've heard this will help as it has stock ring(s). I don't know if it has one or two rings.

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

Wow im suprrised you got that much of a gain. I didnt get anything like that in fact it didnt seem to make a difference at all. I dont think i raised the exhaust roof anywhere near the .110. It just didnt take that much to get it from 140 deg to 150 degree. I didnt do the eliptical port but stayed mainly with the original port shape. Did you remove the center bar? Its hard to tell as im having such trouble with my test equipment and am not gona make any more tests till my new tach gets here. I have some more cylinders so i should be able to do side by side performance comparisons. Thats a good idea on taking the average of three testing points. One thing that seems to be common on these engines is they lose a couple hundred rpm after running full speed a while and get hot. after cooling at idle and run back up it will produse the same results time and time over. I try to take my readings after it gets hot and the numbers stabilize.

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

jack how did you cc the head. I been wondering what the best way to do this is.

damn so much to do and so little time to do it lol.

Duh i just realized i am working on a different cylinder than you have and thats why my port timming is different. I am wondering if your mistake of 160 degrees isnt a blessing in disguise lol.

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

My motor is the newer style with the integral fan shroud, which I've cut off completely. It has the bifurcated (two runners per side) transfer ports and an exhaust port with no bar, and also a 2 ring piston. If you take off the muffler and rotate the engine you can see if the piston has two or one ring and also if the exhaust port has a vertical bar separating the port. The two ring pistons are good. The ring end gaps are very small (I haven't actually measured it) and seals very well. If you then take out the spark plug and shine a light into the cylinder and rotate the crank until the piston is at the bottom of it's stroke you can see the transfer ports and determine if there are one or two on each side. The only complaint I have with the bifurcated transfer ports is the large blunt forward facing edge at the opening to the ports. I made substantial modification to this area in attempt to smooth the flow going into the transfer ports from the crank case. Unfortunately I did not get back to back performance data for that mod. See posts #134 and #145.

My muffler is stock except for a 1/2" piece of EMT electrical metal conduit welded into the original opening.

As for spark plug gap I'm not even sure what it is but .020" sounds about right. I don't think the gap is super critical.

Although I haven't tried a 11.1mm bore carb, mine is 12.7mm, I bet it's fine. av8tor1977 is using a 11.1mm carb to good effect.

If, in fact, you have the same set up as me, I would try the exhaust porting mod next, if you're up to it! The effect on my engine of the exhaust port mod was significant and if you want more power I'd try that first.

If you've got a different version of the Ryobi motor I have no experience and couldn't say what would be the best mod to try first. combatpilot has done a lot of work with the older style motor and might be able to give some input. If you read all the posts in this thread you might be able to glean some info on what mods work best and which ones are not a big pay off.

diceco

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

My motor's stock exhaust port timing was 128deg. The exhaust port of the older and newer style heads are very different so it might follow that the timing is different too. The stock port had no center bar either and was one continuous open port.

I noticed too that the engine sagged a bit for sustained WOT. On my runs I did let the motor stabilize but the time from pushing the throttle up to WOT and when I took data was probably only about 20 to 30 seconds. This is not a terribly unrealistic time to take data as the amount of time WOT is used in actual flight is only about that much too.

To get head volume I filled a small medical style cup that has cc graduations, with total capacity of only 10cc, with water and pored it into the cylinder, with spark plug installed of course, until it was just at the level of the deck. Then I looked to see how much was left in the cup. A real syringe would be even better. For the deck height I put a piece of bailing wire bent into and L shape that would reach to the side of the cylinder into the spark plug hole of the assembled motor and rotated it through TDC and adjusted the thickness of the wire until it would just barely rotate through with out binding up. The volume then is the area of the cylinder bore times the deck height. The total volume at TDC is then the head volume plus the deck volume, of course.

diceco

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

I believe mine is the same as yours. I had the integral fan shroud which I cut off also. I looked in the exhaust and it looks like 2 rings. It doesn't have the vertical bar in the exhaust port. This engine has compression out the butt. I noticed that mine will sometimes quit if I go WOT then down to idle quickly. I've had it idling around 1860 to 1950 rpm. The idle is exactly consistent. If I keep the idle around 2000 rpm, all seems fine. I might tear down the carb. and check it out as I got it from Ebay and just bolted it on and ran it.
Did you remove the base gasket or just leave it in? I'm not real keen on messing with the exhaust port. I might screw it up and I don't have another cylinder if I booger it up.