Hello guys and gals, first off, let me say that I'm an engine geek. I love all engines, as well as their ancillaries (specifically, turbochargers). I've spent most of my wrenchslinging years with cars, but have decided to take a break and kinda took a fancy to the small four strokes on the market, particuarly the Honda GX 31 and GXH50, and the Ryobi 26cc thumper (or should that be tapper?). After scouring the internet for info on the Ryobis and Hondas, I was lead here and have been lurking for almost a month reading posts and learning all I could about Ryobi four strokes. If you like the four stroke sound, you pretty much have one choice, as far as I'm concerned- the Ryobi. The Honda GX31 is too expensive and heavy, IMO, and from what I've read, those are really the only two four stroke gas engines y'all have used. Something that occured to me was that the 26cc Ryobi doesn't have a whole lot of power. Sure, it'll move a 12- 15 lb. plane around, but not like a two stroke will. But what if that was different? What if that 26cc Ryobi could put out 3 HP?

Anyway, forgive me... I tend to get long winded and start to ramble...

The point I came here to make- I believe I'm very close to developing a reliable, reasonably priced, functional postive displacement supercharger for small engines. How reliable? Change the oil once a season in the pump. How reasonably priced? Around $200- $250. How functional? Well, it's still in the testing phase, and I'm still waiting for the weather to warm up so I can do some extensive testing, and I still need to build a dyno so I can have actual numbers to back my claims, but according to my math, that Ryobi should be in the neighborhood of 3 HP with a take off weight increase of less than 12 oz. I know there's been countless "can I supercharge or turbocharge my engine" threads in the past- these particuarly run rampant in the car boards with the kiddies, and me being a new member and all, I don't expect any of you to believe me. However, let's give myself the benefit of the doubt for a moment... would that be something worth producing for you folks who fly four strokes?

Thanks for reading.

Welcome aboard!!! We love new idea,s here. By the way did you check out the Shindiawa 4 stroke engines. They have a supercharging effect in the manner they operate. Take Care Capt,n

Howdy, Cap'n. I saw a few threads on the Shindiawa mills, but couldn't find much else. I'm not talking about a supercharging effect, though... I mean an honest- to- god- bolt- on- to- an- existing- engine belt driven supercharger that will move a given volume of air for each rotation, as well as compress the charge (something I failed to mention in my post). I can't say for sure, but I don't anticipate any carb modifications, because if it works like a draw through setup on a car, carburetion shouldn't be affected.

Gee, I may have to build another plane to test it out on.

Cool!!!!!

I'm a junkie too. Can't wait to see what your results are.

Doug

Quite a while ago OS had a Roots supercharged 1.2. The originals ran so hard they would wipe out the rod and or the crankpin. So OS put a little tiny carb to limit the HP. It seem like at WOT there was still vacuum in the blower cause the carb couldn't pass enough air.

IF YOU BUILD IT THEY WILL COME....


Sorry, couldn't resist. I love engines too, and would like to see your results. I would love to build something antique, like a Taube, or Eindecker, or AVRO Triplane or something with a four stroke gasser just for the sound; but with enough power to justify the weight of the engine!

Keep us posted,
AV8TOR

Wow! sounds good. can wait to here more.

keep us posted!

Yes, I remember that engine well. One of the reasons, I feel, that they were having issues with reliability was that they used the glow internals. Comparing the crank and rod to the designed specific output of the OS and the 26cc Ryobi, it's evident that the Ryobi is much more durable. One of the things I thought about last night after I logged off was that there are two basic types of 26cc Ryobi engine- the half crank (700 and 800 series) and the full crank (1000 series). I'm not sure how much boost this engine will handle, but I surmise that the full crank would be a much more durable engine. I plan on testing both engines, as well as a few piston ported two strokes, such as an old 21.5cc Echo I have laying around.

As for the vacuum in the blower, I'm not sure what you mean by that. Roots blowers are positive displacement pumps, meaning that they always move the same volume of air per rotation, regardless of speed. I suppose that there would be some vacuum between the carb and the blower if the carb was a restriction? Since they don't compress the charge, the only way they produce boost pressure is by overdriving. In a nutshell, if an engine needs 3 CFM at 7000 RPM, and the blower moves 3 CFM at 7000 blower RPM, with a 1:1 ratio, there will be no boost. However, if you were to spin the blower at 14,000 RPM (1:2 ratio), you'd start to see boost. I can't recall the formula to calculate boost with a postive displacement blower, and I'm at work, so I don't have access to my books and notes, but a rough estimate would put that at about 4 PSI, depending on thermal rise of the charge and the VE of the blower. The downside to a Roots blower is that no matter how you cut it, efficiency is in the 50% range, which is poor and lends itself to high intake charge temps.

The blower type I'm using is, as I said before, a postive displacement pump that compresses the charge, so overdriving may not be nessicary. It entirely depends on the efficiency of the design. I have a few different impeller and housing designs I plan on trying.

Something else that occured to me while typing this was a reduction drive for the prop. We all know that big, slow props are more efficient (not to mention quieter) than small, fast props. Now, what if we had this 3 HP 26cc supercharged four stroke putting out a TON of torque through a 2:1 belt reduction drive? The engine can still breathe in the middle of the powerband, and you can have a nice big scale prop.