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  1. #1

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    YS FZ70S-4C vs. OS 91-4C

    Is anyone using this YS FZ70S ? Comparing, looking at spec sheet's only, this YS only weighs 17.4 oz. with muffler, the OS is 24.6 oz. with muffler. Exact weight can be figured in gram's.

    OS $379.95 RPM range per spec sheet........... Up to 11K RPM

    YS $319.95 " Up to 15K RPM Both of these are pumped.

    I cannot comment on these spec's, as fuel, prop's, plane choice, etc., will factor in. Wouldn't this YS be a good for SPA application ?
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  2. #2
    autoguns's Avatar
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    RE: YS FZ70S-4C vs. OS 91-4C

    I have a FZ63s and it kicks azz....It'll turn a APC 14x4w with no problem. in short pound for pound the YS will kick the OS 91's butt all day long.

    The YS 70 "if its anything like the 63" the comment above applys +


    JW
    AKA: The Tim Allen of the hobby

  3. #3

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    RE: YS FZ70S-4C vs. OS 91-4C

    From the rules:

    3. Engines

    a. Any side exhaust two cycle engine up to .61 cubic inches is legal
    b. Four cycle engines up to .91 cubic inches with no air chamber or super charging or any kind are legal
    c. A proper muffler must be used but tuned pipes are not legal d. Pumps may be used but no oversized carburetors can be used.

    Based on this, I don't think either engine qualify.
    Lawn dart professional...
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  4. #4

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    RE: YS FZ70S-4C vs. OS 91-4C

    The YS 70 is an hardcore performance engine, makes unbelievable power for itΒ΄s size and throttle response is in another world compared to the OS. The best engine for 40-50 sized planes period.

  5. #5

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    RE: YS FZ70S-4C vs. OS 91-4C

    What's the suggested tank size for this Yamada?

  6. #6

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    RE: YS FZ70S-4C vs. OS 91-4C

    This may be a bit off topic but I have several "40" sized profiles ( Chinn yaks aeroworks mojo etc) with Ys 63, Ys 70 and an OS 91 Surpass. I realize this is not the new OS engine but I think the following statement applies to the overall performance of these engines although it might not fit the "SPA" aspect of things. In my experience in 3 D, power to weight is everything. If ever there was an engine that combined the overall power and top rpm of 2 cycles with the wonderful instant throttle response across a broad range of throttle settings it would be the YS 4 strokes. Frankly the 63 is plenty for most of the smaller 3d's i fly. The 70 is actually overkill and its actually harder to hover with it in the nose because it is so powerful one click either way and you are climbing out of a hover ( this is with a 14x4 W apc I may need to go to a 15x4W!)

    The Chinn Yak I have with the 91 surpass is wonderful as well but the 91 is just more sedate. I doubt the OS engineers have added that much power to their new engine. I can also tell you rpm wise and in flight the YS 70 outperforms an ASP 80, the Saito 82, the OS ax 55 2 stroke and is comparable power wise to the AX 65 same prop but with a much broader throttle response as you would expect. All of these engines are great though in my application and most are far less expensive. With YS you are also paying for some metallurgy as these engines are surprisingly light. It seems there are a lot of pattern guys who love the power to weight of the YS engines as well.Dave

  7. #7

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    RE: YS FZ70S-4C vs. OS 91-4C

    The .91 Surpass II pump was the engine of choice in SPA. Will be curious to watch as they(OS) dropped it and released the .95 The YS.91( Pressure System) was not SPA legal and I'm sure that thinking will probably continue. I don't have an axe to grind, I just love any and all engines. Talking about them excites me! I think the YS .70 would be awesome in those old designs. What prop do you think it would like?

    turbo

  8. #8

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    RE: YS FZ70S-4C vs. OS 91-4C

    It is not the YS fuel system that is not allowed in SPA, it is the supercharging created by the down stroke of the piston combined with the timing rotor that compresses the fuel/air charge. Never understood what the hangup was since the price difference between the OS and YS engines in the .91 sizes were pretty negligible.
    Has anyone ever actually got a reason as to why YS 4 strokes aren't allowed, other than "they said so"?

  9. #9
    Sport_Pilot's Avatar
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    RE: YS FZ70S-4C vs. OS 91-4C


    ORIGINAL: JeffH

    It is not the YS fuel system that is not allowed in SPA, it is the supercharging created by the down stroke of the piston combined with the timing rotor that compresses the fuel/air charge. Never understood what the hangup was since the price difference between the OS and YS engines in the .91 sizes were pretty negligible.
    Has anyone ever actually got a reason as to why YS 4 strokes aren't allowed, other than "they said so"?

    The SPA wants to keep power and costs down. That is the only reason, they don't have a problem with YS other than that. Pressurized systems are ok but when it comes from a manufacture it usually comes with the oversized carb which is not OK.
    Glow Head Brotherhood #15

  10. #10
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    RE: YS FZ70S-4C vs. OS 91-4C

    This rule goes back a long way. At the time it was created, YS engines were much more expensive than OS and other brands. Keeping with founder Mickey Walker's idea of simplicity and wanting to avoid an expensive horsepower race, this rule was put in place. Times have changed, as have relative prices and availability of certain sizes. But tradition dies hard. At some point we may need to reevaluate the situation.

    Jeff
    Skylane N9214G
    SPA L243 CPA 84

  11. #11

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    RE: YS FZ70S-4C vs. OS 91-4C

    guess its time for a change, the os91 surpasses were modded with oversize saito valves, run on thirty percent nitro etc etc, so the cost difference was a wash, now the new os95 isnt any cheaper but has less power......[X(] tut tut using the ys 70 would make it simpler, as one likely wouldnt have to stretch the tail on many of the designs, a reduction in weight, etc etc, the cost seems to have been a lost cause long ago........

  12. #12

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    RE: YS FZ70S-4C vs. OS 91-4C

    Thanks for the explanation of the fuel system reason for not allowing YS. I always thought it didn't make sense. Would love to see them allowed.

  13. #13

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    RE: YS FZ70S-4C vs. OS 91-4C

    I read it as oversized carburetors are something that the owner changed. If it came from the factory with a certain carb, then it is not oversized, it is OEM equipment. The cost argument is pretty much over these days. People are/were modding their OS 91s, having custom built stretched airframes, flying with 12x or 14MZ radios, digital coreless uber$$ servos etc etc.

    No matter what the sport, people with the money will spend it. The only way to control costs is to run spec engines and spec airframes. The engines would have to be subject to tear downs or some sort of claim rule and the airframes must weight X pounds, and must have X dimensions. Who would really want to fly by those rules??? Not me.
    The engine rules will have to be changed this year since the only .91 size 4 strokes that are available are Chinese if I am not mistaken. The OS is gone, the Saito is backordered and YS, if legal, only has the 115. That leaves used engines or ASP/Magnum or Thunder Tiger?

    My vote is for .65 two strokes since the OS .61 is gone, and 1.00 four strokes, period, end of engine rules. Granted that leaves out new YS engines, but you could run the YS 91s if you so choose. The individual CD should have the right to allow tuned pipes or not based on his local noise issues. In my ideal world, the airframes should match the original's wingspan and length to at least try to keep something consistent with the idea of the SPA. And for the love all things holy, allow retracts lol. (foamies have retracts as standard equipment these days!!)

    One could argue all day about these rules. If you allow modern engines, 4 strokes specifically, you might as well allow modified airframes. Where is the cut off?

    rant over....

  14. #14
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    RE: YS FZ70S-4C vs. OS 91-4C

    You haven't seen their airframes? Modified is a polite term for it!
    Chris...

  15. #15

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    RE: YS FZ70S-4C vs. OS 91-4C

    lol, I have seen pictures of the extreme DBs and have heard about some other airframes stretched here, stab lowered there etc etc. You can do that, but don't you dare use them there fancy retractable landing gear.

  16. #16

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    RE: YS FZ70S-4C vs. OS 91-4C

    Boy, if they would allow a YS70 I would buy one TODAY!!!!!! Would save me a lot of headache.
    WOh yeah, those fancy retractable landing gear are fine, as long as you keep them DOWN (and yes, that does mean they will be watching the whole flight). I asked if it would be o.k. to pull them up on the flyby....of course he said NO.

    Tragic....Tragic...
    Lawn dart professional...
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  17. #17
    dphill2's Avatar
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    RE: YS FZ70S-4C vs. OS 91-4C

    My son used a 15.00 stock Kaos that he got @ the Perry Ga swap meet. (it came with retracks) he was ask many times by some of the judges to pull the gear up while flying in SPA contest.
    I think there are a lot of guy's out there that like the looks of a fast pattern plane with the wheel's in the wells, I'm one of them. As for the OS91 they must have made two different one's because my out of the box Motor never ran as good as some of the crafty ole fox's who have a special motor builder tune at least 1000 more RPM out of em. and I'm sure it was not free.
    As for the YS the only reasion that I have heard is "cost and supercharging." The cost thing is gone and ya need the supercharging to keep up with the Mod 91's.
    O yeah, we both fly two strokes and love em...
    Dave

  18. #18
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    RE: YS FZ70S-4C vs. OS 91-4C

    It was ten dollars. But who is counting?
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    P-51 Mustang Brotherhood#10


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