2 stroke alternative ?

Discussion in '2-Stroke Aircaft Engines' started by MadProfessor8138, Jun 6, 2019.

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  1. Jun 29, 2019 #61

    poormansairforce

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    I've been saying for a while that the HKS 700 isn't anywhere close to 60 hp. The calcs don't support it.
     
  2. Jun 30, 2019 #62

    pictsidhe

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    HKS700 piston speed at 6200rpm takeoff power: 2440 fpm
    yz250F @11,000 : 3870 fpm

    The HKS is designed for sustained full power use. The Yamahas are built for off road bikes, which don't see their throttles pinned for more than a few minutes by unusually crazy riders.

    The utter lack of any engines lasting a decent time at high piston speeds suggest that the screamer conversions are currently doomed.
    Try running one for 100 hours at high power before even trying to convert. A few brief dyno pulls and single digit flight hours are unconvincing.
     
  3. Jun 30, 2019 #63

    pictsidhe

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    Why not? BMEP is in the achievable range for a 4 valve engine
     
  4. Jun 30, 2019 #64

    poormansairforce

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    If you can get a VE of 120% then yes but I don't buy it based on the prop its running. And the thrust to hp has been noted.
     
  5. Jun 30, 2019 #65

    MadProfessor8138

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    I guess I'm an unusually crazy rider than...and everyone else that has ever ran an enduro race.
    Generally,once the clutch drops and you hit top gear......its wide open until the check point is reached or the fuel runs dry.

    My old YZ 490's have been through MANY races and are still going strong after 30 years of being beat like they are step kids.........

    Kevin
     
  6. Jun 30, 2019 #66

    pictsidhe

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    It's BMEP of 180psi.
    For comparison: Current VW petrol engines maximum MEP range 168 to 193 psi.

    The HKS is bang in the middle of that spread. Do you really think that VW are getting away with fluffing their torque figures of many of their engines? You can bet that other major manufacturers aren't much different on their current 4 valves, either.

    HKS claims are nothing special with current tech.
     
  7. Jun 30, 2019 #67

    pictsidhe

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    Just how many hours have you managed to run one of your engines at full throttle, without changing more than oil, filters and plugs?


    The proof of the pudding is in the eating. I've never seen a highly strung bike engine run hard last long enough to be a viable aero engine.

    If you think you can persuade one to live a reasonable life, go ahead and prove us skeptics wrong. or at least point to someone else who has managed it.
     
  8. Jun 30, 2019 #68

    BJC

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    VW never would fluff their engine performance figures ..... https://en.m.wikipedia.org/wiki/Volkswagen_emissions_scandal


    BJC
     
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  9. Jun 30, 2019 #69

    poormansairforce

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    Lets see, a 503 makes 49 hp at 6500 rpm. And a quote from this site on Powerfin props:

    This prop runs beautifully on a Rotax 503/3.47 as a three blade 66"-70".


    So it turns a bigger prop to a higher rpm with the same gearbox as the HKS. Props are dyno clubs so just seeing what one engine turns vs another will help you see through all the bs. Thats why I keep looking for the prop size used by the O-100.
     
  10. Jun 30, 2019 #70

    pictsidhe

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    You can't compare the power absorbed by different props. Compare the chords of the arplast and powerfin props and you may realise that they are not close kin.
    Put the exact same prop on 2 different engines without changing the pitch, then you have a comparison.
     
  11. Jun 30, 2019 #71

    henryk

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    =LADA PRIORA, 250 HP...430 kG thrust at 5300 RPM.
     
  12. Jun 30, 2019 #72

    Victor Bravo

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    My Arplast prop was three blades and significantly wider chord than Powerfin, Ivo, etc. I picked this because I had a max diameter limit of 65" and all the prop manufacturers told me my engine and gearbox combo needed a 71-72 inch 2 blade prop. So please do not use my example for or against the HKS making X amount of power.
     
  13. Jun 30, 2019 #73

    poormansairforce

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    Go to the site I linked and look at the chart for the the 52 hp 503. The smallest prop for the 3.47 gearbox is a 4 blade 65". Which means each blade is absorbing 13 hp. So how many hp is each blade of the Arplast absorbing? 15? 16? Or 20? And factor in a lower prop rpm for the HKS.
     
  14. Jul 1, 2019 #74

    MadProfessor8138

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    Pictsidhe...... I do not have the time nor the money to develop a redrive system.
    I was merely pointing out the fact that an engine is JUST AN ENGINE.
    Run it within its designed parameters and that engine doesn't know or care what its ultimate accomplishment is....it just does its work of creating power.
    How that power is harnessed and utilized is what determines whether or not that engine will live a short life or a long one.
    Here's an example that might help clarify my viewpoint for you.....
    Chevy small block v8....let's say a common 350.....you will find that engine in cars,trucks,race cars,airboats,boats,airplanes,motorcycles,lawn mowers,saw mills,farm implements....etc.
    That engine could give 2 sh*ts less as to what its application is.....run it within its designed parameters and it will produce power without complaints.
    For each one of those applications they have found the proper way to harness the power......the redrive.
    The engine is nothing special.....the redrive IS THE KEY TO SUCCESS.

    As far as the engine on my YZ490.... never figured up the actual milage nor the hours....2-3 races a year at 200 - 400 miles each for the past 20 years....throttle pegged between check points....well,you do the math.
    Plus,I still ride it when I'm not racing it so milage and time is constantly changing.
    I've broken chains,flattened tires,had a few clutch springs start to get weak,had reed valves crack....etc.
    But no,no internal engine damage ever....piston,rings,rods, crank ...etc.
    I've never not finished a race.
    Back in 2005 I changed to a different piston/ring and sleeve manufacturer which prompted a semi-tear down....but that was only because of my personal preference...not because it needed to be done.
    If you ever want to come out and run an enduro with us....I have a KDX200 that will keep you at the front of the pack and make you look good while you're doing it.
    If you can prove to me that you have the ability to twist the wick on the bike and hold it wide open until the fuel runs out....I promise to have the ability to show you an engine that still runs like a champ when you throw some fuel in it and twist the wick again until the next fuel stop......rinse and repeat.

    Kevin
     
  15. Jul 1, 2019 #75

    BBerson

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    If you run full throttle continuous, what keeps it from exceeding redline or blowing up going downhill?
    Is it on the backside of the hp curve or something that limits rpm?
     
  16. Jul 1, 2019 #76

    MadProfessor8138

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    BBerson......that's a pretty straight forward question that has a very curvy answer,unfortunately.....
    Here are things that limit rpm on 2-stroke engines in dirt bikes........
    1. CDI box set rev limit.....mine has been replaced with aftermarket box 20 years ago and will rev to the moon.
    2. Exhaust pipe......my pipe is tuned for mid-range and top end power.
    3. Reed valves.....I still prefer metal reeds over the composite...hard to find metal now days though.
    4. Carb jets and needle position....the YZ490 is a notorious pain in the ass to jet...those of us that can do it properly are few and far between.
    5. Carb float level....if it's set low the engine starves...if it's set high the engine bogs from being too rich....its a fine line to find the sweet spot.
    6. Air filter and box...if it can't breath then it can't make power.
    7. Fuel....I can make more power with less octane because the spark front isn't slowed down by the high octane....but sometimes higher octane needs to be ran to stop pre-ignition and venting a piston....temp,altitude and humidity come into play.
    8. Gearbox ratio,sprocket sizes and tire sizes.....you can only spin things so fast until you can't overcome the resistance with the given hp and torque.
    Mathematical calculations come into play here.
    9. Sparkplugs.....hot or cold .....this changes the ignition timing by affecting the the fuel burn...retard or advance.
    10. Head gasket thickness.....compression can be bumped up or lowered down by varying the thickness of the headgasket.
    I've shaved them down to bump up and I've ran double gaskets to lower compression.
    11. 2-stroke oil.....full synthetic or not ?
    Every engine and every mechanic has their own preferences to flavor.
    This affects bearing life,engine temp and carb jetting.......better get it right.
    12. Flywheel weight......a heavy flywheel lugs the engine which is good for work in the sand/woods and hills but a lighter flywheel is desired for crisper throttle response while going head to head with another racer on open,curvy and short distance stretches.

    As you can see.....setting up an Enduro or MX engine is more complicated than realized by most people.
    EVERYTHING that I listed affects EVERYTHING else on the list....change one thing and you go from a sweet running engine that has been leading the pack all day to an engine that makes you want to kick the piece of sh*t into the nearest ditch and walk to the next check point.
    It's not unusual to see guys carrying extra plugs,jets and flywheel weights with them and to stop at some point during the race and make changes as the course changes.....elevation,temp,humidity,fuel quality,ground lay out...etc.

    Setting an engine up for aircraft use is somewhat simpler because the operating conditions are pretty consistant from day to day.
    There are different jetting charts for summer/winter season and charts for elevation but many of the Rotax carbs,and others,are altitude compensating now and take that issue out of the hands of the operator.
    Gearbox and prop should stay the same once set.
    Plugs will remain the same once set.
    Etc.........

    Did that come close to answering your question ?

    Kevin

    One more tid-bit of info......
    Some of the strongest running engines are also the most fuel efficient.
    This is because they have found that magic combination of air,fuel and spark to be able to convert the fuel into usable power.
     
    Last edited: Jul 1, 2019
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  17. Jul 1, 2019 #77

    BBerson

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    Well no. I misunderstood and thought you were talking about high rev four stroke motorcycles, since this thread is "two-stroke alternatives". I guess a two-stroke can't over-rev and fail when the pistons hit floating valves.
     
  18. Jul 1, 2019 #78

    MadProfessor8138

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    I thought you were asking about my YZ490 engine......sorry.

    On the 4-stroke engines they use a rev limiter and timing chain to keep the valves and pistons from getting to know each other.
    However,there are interference engines and non-interference engines.
    An interference engine will have the valve hit the piston if things get out of time....valve float/timing chain issue...etc.
    While the non-interference engine will valve float if over revved...the valves and the piston wont become intimate friends.

    Closer to what you were asking ?
    Lol.....

    Kevin
     
  19. Jul 1, 2019 #79

    Vigilant1

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    I know it well, that's how I always raced my minibike. Full throttle starting at Billy Breen's house and keep that 3 HP B&S winding out until I reached the Tastee-Freez. I could do it until my 32 oz tank ran dry, maybe 45 minutes
     
  20. Jul 1, 2019 #80

    BBerson

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    Well yes, if they have a rev limiter that means the motorcycle engine isn't automatically rpm limited like an airplane with a direct drive prop load. Airplanes don't have rev limiters. Airplanes with direct drive in climb are what we might call "lugged". ( not able to increase rpm)
    If you run full throttle but with a rev limiter it isn't always really full power (Max manifold pressure like a " lugged" airplane engine.
    I think that's the difference between airplane and motorcycle operation.
     
    Last edited: Jul 1, 2019

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