Piston Port to Reed Fed Conversion

Discussion in '2-Stroke Aircaft Engines' started by Armilite, Mar 3, 2019.

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  1. Mar 3, 2019 #1

    Armilite

    Armilite

    Armilite

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    Your Rotax 185UL, 277F/277UL, 440F/447UL, 503F/503UL, are Piston Port Engine's, the 462UL, 532UL, 582UL, 618UL, 670, are Rotary Valve Engines.

    The 277F/277UL, 503F/505UL, and the Skidoo 550F Reed Fed Engine all use the same Head/Cylinder Bolt Pattern. A Reed Fed Engine will outperform a Piston Port Engine.

    250(72mm x 61mm) 248.4cc
    277(72mm x 66mm) 268.8cc
    503(72mm x 61mm) 496.9cc
    550(76mm x 61mm) 553.6cc

    Most Reed Fed Engines the Reed Valve is on the Engine Case. On the Skidoo 550F, it's on the Cylinder. The 550F Cylinder & Case has a Small Port that the 277/277UL, 503F/503UL doesn't have, but you have a choice, add the Small Port on the Case, or Block off the Small Port on the Cylinder and use a Piston with Side Window Port. So what all does this get you.

    On a 277(72mm x 66mm) 268.8cc, with a 550 Cylinder, Piston & Rod (76mm x 66mm) 299.5cc. Some Minor Port Work needed for the different Stroke.

    On a 550 Cylinder with a 250 Type 253 61mm Stroke Crank (76mm x 61mm) 276.8cc.

    On a 503(72mm x 61mm) 496.9cc. With a 503F/503UL Bottom, with 550 Cylinders gets you a (76mm x 61mm) 553.6cc Engine. Stock Cylinders can be Bored 2mm.

    A 2004 550F with 34mm Carbs, Dynoed 70hp@7000rpm using Stock 9.6cr. So at 6500rpm it should make 65hp. Bump the CR up to 11.6 and gain about 4hp = 69hp! 550F's have been Big Bored to 81mm using an Arctic Cat Piston. (81mm x 61mm) 628.9cc.
     

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    Last edited: Mar 3, 2019
  2. Mar 3, 2019 #2

    Armilite

    Armilite

    Armilite

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    A Stock 503UL (72mm x 61mm) 496.9cc, rated 50hp@6500rpm, with an R&D Tuned Pipe made 62.3hp@6500rpm!

    The Stock 503UL actually Dynoed 49.8hp@6250rpm! 62.3hp - 49.8hp = 12.5hp Gain! 49.8hp +25% = 62.3hp. So 25% would be considered a very Mild Tuned Pipe.

    If, you bumped up a 503F/503UL from 10.8cr to 11.8cr = 2hp Gain. 62.3hp +2hp = 64.3hp! A Stock 582UL Actually Dynoed 64.7hp@6250rpm.

    A 550F with more CC to work with. If 550 is 65hp@6500rpm +25% = 81.25hp!
    The Weight Savings of Fan Cooled vs Water Cooled and the extra Cost.

    Your 582UL can make more HP also with a Good Tuned Pipe. With R&D's best Tuned Pipe for the 582UL it made 80.7hp@6500rpm. 64.7hp +25% = 80.8hp. So it's a Mild Tuned Pipe also.
    http://www.rotaxservices.com/dyno.html#3
     

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  3. Mar 3, 2019 #3

    Armilite

    Armilite

    Armilite

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    Rotax 582UL with a +25% mild Tuned Pipe made 80.7HP@6500rpm vs Stock 64.7hp@6250rpm.
     

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  4. Mar 3, 2019 #4

    Armilite

    Armilite

    Armilite

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    For comparison a newer 600 eTec is 115hp@8000rpm, the 600HO is 125hp@8000rpm. Notice, how it has a terrible Factory Exhaust. Dead Spot between 6400rpm and 6500rpm.

    Compare that to a Good Tuned Pipe on a 380HO/377/377UL making 57.26hp@7000rpm. It's not perfect either, a small blip at about 5900rpm but not bad. A 380HO use's 11.2cr vs 9.6cr the 377/377UL use's.
     

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    Last edited: Mar 3, 2019
  5. Mar 3, 2019 #5

    pictsidhe

    pictsidhe

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    Reed's will widen the powerband compared to piston port and make starting a lot easier. They do nothing for peak power. A plane doesn't need low end Powe so the only benefit will be easier starting. I did like the extra low end I got on my MZ motorcycle I converted and it was much easier to start afterwards, but no extra peak power.
     
  6. Mar 4, 2019 #6

    Armilite

    Armilite

    Armilite

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    ==========================================================

    Your Motorcycle with a Multiple Geared Transmission is going to work differently than a Prop on an Engine at a set Ratio/rpm.

    A Piston Port vs a Reed Port vs a Rotary Valve will start the same usually (1-2 Pulls) if properly Tuned (Points or CDI) and if Primed/Choked right! Like my Skidoo 670 if I haven't started it in a Month, just hit the Small Primer Bulb 10 times, and it will Start in 1-2 Pulls. With an Ultralight that hasn't been started in a while with a Big Squeeze Bulb, maybe 4-5 Squeese's and it will kick over. Most of hese Engines use Fuel Pumps run by Vaccum. Some Ultralights have both a Standard Vaccum Fuel Pump and Primer, and some have an Electric Fuel Pump.

    The vast Majority of Ultralights and Kitplanes need 18+hp to maintain level Flight, with the Rotax 277UL Single being the most used. It makes 18hp@5000rpm. Twins like the 377UL, and 447UL make 20hp around 4500rpm, the 503UL makes 20.2hp@4000rpm! So it's pretty Safe to say these Engines use 4000rpms to Max 6500rpms.

    When you look at Racing Statistics, the Yamaha 292 Reed Fed Single, Dominated the Class over all the other 292's about 20 different Brands, that were All Piston Ports. The only Engines to beat the Yamaha 292 Reed Fed Singles was the Small Rotary Valve Twins. Skidoo/Rotax never made a Production Reed Fed Single or a Rotary Valve Single.

    They did make this (78mm x 70mm) 334.6cc Rotary Valve Single prototype in 1969, 39hp@7000rpms RV Single with a Muffler! Basically a 1/2 670 that came out 14 years later. A 1993 670 (78mm x 70mm) 669.2cc is 115.7hp@7750rpm. The 670HO was like 125hp@7750rpm. So a Standard 334.6cc Rotary Valve Single with a Good Tuned Pipe would probably be around 57.8hp@7750rpm.

    I believe a Reed Fed Engine just has Bigger Ports than the Piston Port Engines so they Breathe Better.
     

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  7. Mar 4, 2019 #7

    pictsidhe

    pictsidhe

    pictsidhe

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    Tuning a 2 stroke is much more involved than improving the breathing. If you ever get around to actually trying to tune one, you'll find that out PDQ. Meanwhile, I'm going to trust my actual experimental results and those of other experimenters over your armchair theories.
    Try starting a race tuned piston port and race tuned Reed engines then tell me there is no difference in starting.
     
  8. Mar 4, 2019 #8

    Armilite

    Armilite

    Armilite

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    First Off, Pictsidhe were not Talking, Building, Tuning, Comparing, any Motorcycle Race Engines here. This is Home Built Airplanes that use 2 Strokes at Max 6500rpm! So yes, keep using your actual experimental results and those of these other so called experimenters and you might really learn something, but it's apparent you haven't learn too much so far. Like I told you before, READ, that Book I gave you the Link to, actually Buy, or Find, a Rotax 2 Stroke, and put your Theorys to work. Book Link, http://www.amrca.com/tech/tuners.pdf

    2nd, Pictsidhe for someone who has said, they have never Built or Owned a Rotax 2 Stroke, or even used one on an AirPlane! You have a bunch of Opinions! Talk about Armchair Theories from a Armchair Mechicanic. Did you even Read that Book I suggestted yet? http://www.amrca.com/tech/tuners.pdf Making more HP is all about Improving Breathing using Porting, CAM's, Valves, better Exhaust and Air Filters! Until maybe just recently, you said you got a used Honda/Briggs to exsperiment on. You keep talking about exsperimenting on one of these cheap Honda/Briggs/etc, but yet No Info, No Photo's, No Actual use with one on any Plane. Do you even have a Plane yet?

    As I said, there is No Difference in Starting a Piston Port vs a Reed Fed vs a Rotary Valve 2 Stroke Engine, if it's Timing is Correct, Plugs Clean, and Ignition parts and Fuel System are all working properly, if you know what you're doing! Apparentlyy you do not.

    My 2 Strokes:
    2 Stroke Lawn Boy Mower
    2 Stroke Weed Wacker
    2 Stroke 503UL on T-Bird I 50hp Electric Start
    2 Stroke 1993 Arctic Cat 580 EXT 80-85hp <--- We Started it in -1 Degree's and rode it 2 days ago!
    2 Stroke 1994 Yamaha 600 V Max 95hp <--- We Started it in -1 Degree's and rode it 2 days ago!
    2 Stroke 1995 Yamaha 600 V Max 95hp Electric Start <--- We Started it in -1 Degree's and rode it 2 days ago!
    2 Stroke 1972 Skidoo 292 TNT 20hp
    2 Stroke 1976 Arctic Cat 275 20hp
    2 Stroke 1997 Skidoo 670 115.7hp <--- We Started it in -1 Degree's and rode it 2 days ago!

    I have about (12) other complete Skidoo/Rotax 2 Stroke Engines sitting in my Shop, and enough Parts to probably assemble another 4-5 engine's. Mainly Singles, 247, 277UL, 299, 335/340, and some Twins mainly 377's and 503's, and I have (2) 670's and (1) 617.

    I only got a 427, and a 454 Chevy Big Blocks left, and a 350 Chevy Small Block, and half the parts to maybe assemble another Big Block. Two of the Engines are for 55 Chevys I have. The last Engine is for my last Hot Rod Project, thinking a Dually Truck.

    I learned PDQ, you don't know much about Rotax's or any other 2 Strokes for that matter, but you always have an opinion about them! You can't even look up the Install Weight of a Rotax 277UL vs these Honda/Briggs GX390 Singles to give an Informative Correct Answer! READ a POST, THINK, DO RESEARCH, then REPLY.
     
  9. Mar 9, 2019 #9

    pictsidhe

    pictsidhe

    pictsidhe

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    Reality is the stuff that won't go away when you stop believing in it.
     
  10. Mar 24, 2019 #10

    Armilite

    Armilite

    Armilite

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    Just a Small Part of my Reality.

    MY 340 TNT ENGINE.jpg MY 1972 292 TNT RACER.jpg MY 340 TNT ENGINE.jpg MY 1972 292 TNT RACER.jpg MY MILL.jpg MY 277UL.jpg MY 617.jpg MY 340 TNT ENGINE.jpg MY 1972 292 TNT RACER.jpg MY MILL.jpg MY 277UL.jpg MY 617.jpg SPARE ENGINE PARTS.jpg MY 335 SINGLE.jpg MY PLASMA CUTTER.jpg
     
  11. Mar 24, 2019 #11

    pictsidhe

    pictsidhe

    pictsidhe

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    Armelate. I' sorry for intruding in your topic. I honestly thought that you and others might find the results of the conversion and testing of a 291cc 26hp engine from piston port to reed valve interesting. I should have realised that because the size and horsepower are way, way different AND it was made hundreds of miles away by a different manufacturer for a ground vehicle, my results weren't even worth mentioning. My bad.

    To everyone else, sorry about the run on sentence. I can't be bothered to fix it.
     
  12. Apr 1, 2019 #12

    Armilite

    Armilite

    Armilite

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    =======================================================================

    Most of these Small 2 & 4 Stroke Engines used for Ultralights & Kitplanes were Designed for Ground Powered Unit's, like Snowmobiles, Go Carts, Generators, Water Pumps, Scat Hover Craft, Cars, etc. Most people here, don't Rebuild their own Engines, let alone do any Exotic Modifications, like Big Bores, and Cylinder Swaps, or even make a Tuned Pipe. Why I don't know, they will jump right in to Build a Kitplane and most have never done that before. I have been rebuilding Engines since I was around 10 years Old. A (1) Cylinder 2 Stroke 50cc Bicycle Engine was my first Engine. Did some Briggs Go Cart & Mini Bike Engines shortly after. Took a Small Engine Repair Class in 9th grade doing mower Engines. Helped my Dad & Neighbors work on their Cars, Trucks, Boat motors, also doing Brakes, Transmissions, Shocks, Exhaust, Clutches, etc. So it was normal for me to do my own work, buy the Tools needed. I Bought my own first car when I turned 16 and did all the work on it. Bought my 2nd car a 70 SS Camaro with a 402 Big Block and street raced it almost nightly. Over time I Rebuilt that Engine 2 times(Broke Piston), Head work 3 times(Broke Valve Guide, Bent a Valve) I shifted it at 7000rpm. Souped it up to about 600hp, rebuilt the complete Tranny with a B&M Street/Strip kit, also replaced every Body part but the Hood, Roof, Doors, and repainted it twice. Since then I have done many other cars & engines. Kids aren't working on Cars/Trucks/Sleds/Planes/Boats/etc., either these days. Today you have some good Books, Video's, on How to do almost anything you want to do. I even built my own House & Garage started it at age 25, took me a year. These 2 Strokes aren't complex Engines. Read some Good Books, Watch some Good How to Video's, buy the Tools needed and jump in. There is an Engine for every Budget!
     
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  13. Apr 27, 2019 #13

    Brian Musil

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    A Reed valve motor doesn't tend to spit fuel back out the carb at you and they have better torque. I've run Reed and piston port motors but the big advantage of a Reed motor with a pipe is the second shot of fuel/air the motor will take in during the pipe scavenging phase
     
  14. Apr 28, 2019 #14

    Turd Ferguson

    Turd Ferguson

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    Way back in the '70's you could buy an aftermarket reed valve induction and retrofit to single cylinder engines. We did this on some purpose built racing motorcycles. The real increase in performance was realized by cutting ~10mm off the piston skirt (or reshaping the skirt) on the intake side to allow the intake port to stay open longer. If you got too aggressive and crankcase pressure starting pushing fuel/air back out the induction port before the piston skirt shut it off, the reed valve would stop it from blowing back through the carb.
     
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  15. May 4, 2019 #15

    Armilite

    Armilite

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    I have never seen a Good Fair Test of (2) Engines using the same Bore & Stroke = CC, same CR, same Size Carb, same Air Filter, same similar Tuned Pipe, same similar Porting to really Prove one is better than the other, Piston Port vs Reed Port. The closest was the Old 292 Class of Snowmobiles. Out of about 20 different Engine Brand 292's, (19) were Piston Port and only (1) was Reed Fed, the Yamaha 292 Reed fed Ruled the Race Circuit. The 292 Skidoo was making around 55hp@8000+rpm vs the Yamaha 292 was making 70hp@9000rpm.

    There is always going to be some differences in Port Sizes, Tuned Pipes which have many variables.

    Off Aaens web site. "VINTAGE 292 RACE PIPES.
    We have two pipes available for the popular 292 Yamaha single engine. The full race pipe is developed for modified Oval racing and delivers 70 HP at 9000 RPM with Full Race Porting, Reed Valve intake and a larger Carb. We also have a milder pipe that is turned for 7500 RPM and delivers 50-55 HP depending on Cylinder Porting. This pipe is very popular in One Lunger Sno Cross Enduro Races or for Vintage Trail Riding and Restorations."

    Using the Peak Flow HP Calc. With Case & Cylinder Porting you can Gain 10% - 15% overall hp (Volumetric Efficiency) over Stock.

    A Yamaha 292cc making 55hp at 7500rpm = 106% Volumetric Efficiency.
    A Yamaha 292cc making 70hp at 9000rpm = 113% Volumetric Efficiency.

    A Skidoo 292cc making 55hp@8000rpm = 100% Volumetric Efficiency.

    A guy I know that Races a Skidoo 277F Single, turns his 9200rpm, using 14.5cr, CDI, a Tuned Pipe, and Big Carb, he estimates by his Race Times he's making around 55hp. Peak Flow Calc says 268cc at 100% Volumetric Efficiency is making 58hp@9200rpm. My Stock Skidoo 670(669cc) Dynoed 115.7hp@7750rpm, comes in at 94% Volumetric Efficient.
     

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