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  1. #1

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    .91 Four Stroke Readings

    Post your .91 four stroke tach engine readings, any brand...

    ASP .91
    %10 Wildcat %18 oil

    MA 14x6 8900
    Zinger 14x5 10500
    Philip

  2. #2

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    RE: .91 Four Stroke Readings

    Engine: Saito FA91
    Fuel: Powermaster Heli, 15% Nitro, 20% Synthetic/Castor oil
    Prop: APC 14 x 6
    Max RPM: 10200
    Flight RPM: 9700

  3. #3

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    RE: .91 Four Stroke Readings

    HOMEBREWER reports a THUNDER TIGER .91 FS was reported to turn an APC 14x6 at 10500 on 10%... don't know the other details. The only reason I remembered the numbers was because I wanted to buy one and researched it here first. BTW, I did buy the TT FS 91, but haven't run it yet. I am going to put it in a CMPRO/GSP Spitfire.
    Haywood
    -- My flying skills are just fine, it\'s my judgement that is lacking! --

  4. #4

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    RE: .91 Four Stroke Readings

    os .91 fs pumped
    10% byrons
    10..25 lb topflite 65" mustang

    15 x 6 8200rpm apc "kinda slow"
    14 x 6-10 7450rpm zinger this prop really loads it down on the ground but once in the air it realy picks up speed

  5. #5
    Sport_Pilot's Avatar
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    RE: .91 Four Stroke Readings

    Thuunder Tiger .91 FS

    Fuel Wildcat 15%
    Prop MA 14-6 10,200
    APC 14-6 10,300
    With Coolpower 25% 10,600.
    Glow Head Brotherhood #15

  6. #6

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    RE: .91 Four Stroke Readings

    Some more readings...

    Engine: ASP .91
    Fuel: 10% Wildcat

    Prop/Tach #s:
    APC 14x10 7,600 While it has a low static rpm, it gives pretty good performance in the air
    Zinger 14x8 7,900
    Zinger 13x10 7,900

    My engine is still pretty new(about 1/2 gal.) but I'm not really impressed with my numbers yet. The only prop that will get sufficient RPM is a Zinger 14x5 @ 10,500. Anything with much pitch really loads the engine down.
    Philip

  7. #7

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    RE: .91 Four Stroke Readings

    All of mine to date...

    Engine : ASP .91
    Fuel : Wildcat %10
    Glow Plug: OS #F

    APC 14x10 = 7,600
    APC 12x12 = 9250*
    APC 12x10 = 9500*
    APC 11x12 = 9600*
    Zinger 14x8 = 7,900
    Zinger 14x5 = 10500
    Zinger 13x10 = 7,900
    MA 14x6 = 8900

    Again, my engine is still breaking in, so I'm hoping my numbers will improve
    * = New for this post
    Philip

  8. #8

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    RE: .91 Four Stroke Readings

    ORIGINAL: Sport_Pilot

    Thuunder Tiger .91 FS
    ...
    APC 14-6 10,300
    This works out to be 1.8hp. The TT .91 is rated at 1.6hp. I've never known manufacturers to under-rate their products, do they? I'm just trying to figure out if my enigne is under performing, or if people are inflating their numbers a bit.[:-] Not trying to pizz anyone off, I was just curious.
    Philip

  9. #9

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    RE: .91 Four Stroke Readings

    Saito 91. Fuel 5% Nitro 10% oil (8%syn 2% castor)

    13x8 APC=10200
    12.5x8 bolly= 10700
    Which calculates to around 1.7hp.

  10. #10
    Sport_Pilot's Avatar
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    RE: .91 Four Stroke Readings

    How do you know the HP? From a propeller HP thrust caluclator? Seems .2 HP off is a pretty good estimate to me. Also an honest manufacture would have ratings of the AVERAGE engine, not the best or most pampered engine. But IMO TT made some changes without updating the specs. Their marketing seems off, or maybe their marketing people are just as lazy as their service people.
    Glow Head Brotherhood #15

  11. #11

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    RE: .91 Four Stroke Readings

    ORIGINAL: Sport_Pilot
    Also an honest manufacture would have ratings of the AVERAGE engine, not the best or most pampered engine.
    Well, most don't. They try anything they can to get their HP number up because so many people look at that when buying an engine.

    I did use the Thrust HP program to find the HP. Again, I wasn't trying to make anyone mad, I was just curious. It doesn't seem far off at all now, because I tried an APC 14x6 Sport on my .91 and I got 9700. After my engine breaks in fully I'm hoping to get about 300rpm which would put it close to your number. No offense!

    TT Does need to up their marketing. If their service/marketing was as good as their engines they'd be in good shape

    More #s...

    Engine: ASP .91
    Fuel: Wildcat %10 Nitro
    OS #F Plug

    APC 14x6 - 9700
    APC 13x8 - 9650
    Zinger Pro 14x6 - 8900
    Philip

  12. #12

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    RE: .91 Four Stroke Readings

    Yes, I was routinely getting 10,500 -10,600 k on my TT .91s but if I said it was with 10% fuel, I was mistaken. I use only 15% or 20/20 in my engines.

    The point is that the TT .91 will smoke most engines in its class other than YS. Yes, its a little heavier but most airplanes I built needed the extra weight in the nose anyway.

  13. #13

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    RE: .91 Four Stroke Readings

    i am running 2-OS-91 on 15 x 4 APC i will have to tach as i have forgotten the deal[8D]
    smooth as silk!

  14. #14

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    RE: .91 Four Stroke Readings

    My OS FS-91 II with pump turns MA 14x6 at 9650 rpms.

    Fuel is Model Technics Dynaglo 10% nitro with 14% (enriched) oil (12% synthetic + 2% castor).

    Stelios

  15. #15
    Richard L.'s Avatar
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    RE: .91 Four Stroke Readings

    My OS FS-91 Surpass II with pump swings a Graupner 13.5x8 at 9.6K rpm on Powermaster 15% nitro:

    http://www.WarbirdObsession.com/
    Tamiya Panther, Tamiya King Tiger(3), Tamiya Tiger I, HL Tiger(3), HL Panzer III(2), HL Panther, HL Pershing, HL Bulldog, WSN T-34/85, HE Leopard 2A5

  16. #16
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    RE: .91 Four Stroke Readings

    TT F91S running 10% Wildcat 18% syn/castor blend
    Zinger 15x6 = 8200 rpm
    Zinger Pro 14x5 = 9700 rpm

    OS .91 Surpass II running 10% Wildcat 18% syn/castor blend
    Zinger 15x6 = 8400 rpm
    Zinger Pro 14x5 = 9500 rpm

    Both engines are still breaking in and running rich. Each has about a half gallon through them.
    The OS seems to like the 15" prop better than the TT.
    The TT turns the 14" prop better than the OS.

    I will get an APC 14x6 or maybe a 15x4W and see what I get.
    Anthony
    Murfreesboro, TN
    www.excelsiorweb.com/rcair/
    www.mprcf.com

  17. #17

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    RE: .91 Four Stroke Readings

    Saito 91S, Wildcat 15% 2/4 stoke fuel, Apc 14X6 prop
    peek 10,500K

  18. #18
    Sport_Pilot's Avatar
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    RE: .91 Four Stroke Readings

    Give the TT another gallon or so, its potential is not as apparent till then. If you are not getting over 10,000 with the 14-5, then something is wrong.
    Glow Head Brotherhood #15

  19. #19
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    RE: .91 Four Stroke Readings

    I got an APC 14x6 and ran it yesterday. It was hot and humid and started raining while I was running them. I need a cool dry day to see what they will really peak at. Both are really still getting broken in so I am not too worried about the performance.

    TT F91S running 10% Wildcat 18% syn/castor blend
    APC 14x6 = 9400
    idle was 1800


    OS .91 Surpass II running 10% Wildcat 18% syn/castor blend
    APC 14x6 = 9700
    idle was 1700
    Anthony
    Murfreesboro, TN
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  20. #20

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    RE: .91 Four Stroke Readings

    AnthonyH - nice comparo work - keep it coming!

    For the record, my OS .91 S2 Pump spins a 13x10 APC at 9200 rpm with a stock exhaust and 9400 rpm with an OS EX-502 header.

  21. #21
    Sport_Pilot's Avatar
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    RE: .91 Four Stroke Readings

    Anthony H,
    Wat altitude were you at? Have you checked the valve gap since breaking them in? The TT seems to be getting weaker instead of stronger.
    Glow Head Brotherhood #15

  22. #22
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    RE: .91 Four Stroke Readings

    Sport_Pilot,
    I checked the valves on both the day I ran them. I was giving them both a final go-over before mounting on their planes. My first post was a cooler and dry day. My second post was a hot rainy day. I am at 605 ft. ASL. I think both are still not broken in good and will get better once I get them in the air for about a gallon. I have ran them enough to get stable needle setting and a reliable, low idle.

    I think that .91 four-strokes should be swinging a bigger prop at lower rpm anyway. A four-stroke turning above 10k seems a bit much. A 15x6 gets it in the 8k range which should be more in the power-band on a four-stroke since they make their power more with torque than high rpm. With both engines I cannot tell a difference in the throttle response between the 15x6 and 14x6 so I would say the 15x6 is not too much prop for a .91. What do you guys think? Am I crazy or missing something that is the reason most people use 14x6 on .91 FS?
    Anthony
    Murfreesboro, TN
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  23. #23
    Sport_Pilot's Avatar
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    RE: .91 Four Stroke Readings

    I think that .91 four-strokes should be swinging a bigger prop at lower rpm anyway. A four-stroke turning above 10k seems a bit much. A 15x6 gets it in the 8k range which should be more in the power-band on a four-stroke since they make their power more with torque than high rpm.
    Modern four strokes make more power at hight RPM than they used to. Many now make their best power above 10K My old OS .91 did best just under 10K my TT was happier in the low 10's. As I recall the OS .91 would turn a 14-6 at about 9,800 and the TT would turn it at about 10,200 or so. This was on 10 or 15% nitro. With a larger prop like a 14-8 or 15-6 they were almost the same, but I never compared them side to side with a larger prop. Your manual will tell you the maximum RPM, stay well below that and you will be OK.
    Glow Head Brotherhood #15

  24. #24
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    RE: .91 Four Stroke Readings

    Engine : OS .91 Surpass
    (loooow time, 8-10 tanks)
    Fuel : 15% Omega
    Glow Plug: OS #F


    Prop: 14x6 Zinger
    RPM: 10,200

    Prop: 14x6 Master Airscrew
    RPM: 10,000

    Prop: 14x7 Graupner Nylon
    RPM: 8,900

    Prop: 13x6x10 Zinger
    RPM: 9,900

    Why all the props? Because the darn thing wasn't running right out of the box - only turning in the mid sixes. Re-plumbed fuel tank and lines AND loosened a way-too-tight intake valve. Tried all the props and am running the master airscrew for now. The 14x6 Zinger was best, but it's a loaner. A 14x6 APC is probably the best.

    The engine has easy duty just dragging our big senior telemaster around the patch.

  25. #25
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    RE: .91 Four Stroke Readings

    I can't believe nobody has posted this yet.

    Engine:
    YS .91FZ
    APC 15x6 @ 9600
    15% nitro
    2.0 HP rating
    FLY IT HARD AND HOVER IT LOW!!!

    http://derrick.myphotoalbum.com


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