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08-10-2007 10:49 PM  10 years agoPost 1
T 3d

rrApprentice

Boston Mass

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Whats up guy i have a qeastion what is the differance between the 8.45 and the 8.18 if i have a ys 91st engine.and if i would have to make a change whats involve and how much is the part

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08-10-2007 11:46 PM  10 years agoPost 2
adcnh

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NH

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What bird do you have fury stratus?
8.18 gearing for the OS and 8.45 For the YS, atleast that is what MA recomends.not a big deal to chane, what do you have now for a gear installed ?

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08-10-2007 11:58 PM  10 years agoPost 3
T 3d

rrApprentice

Boston Mass

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gear

fury extreme 8.45 ys 91

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08-10-2007 11:59 PM  10 years agoPost 4
T 3d

rrApprentice

Boston Mass

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gear

ys 91 8.45 gear ratio fury

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08-11-2007 01:33 AM  10 years agoPost 5
adcnh

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NH

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Do you want to put an os in it? if so you will need a main gear, side plates, and motor mounts or you can shim the motor.
P.S. if you need 8.18 motor mounts i have them.

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08-11-2007 01:44 AM  10 years agoPost 6
adcnh

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NH

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0865-90 main gear 24.95
119-118 Raitio Plates 22.70
115-51 Right motor mount 15.42
115-50 Left Motor mount 15.42
115-47 Mouto shims 2.68
Total 81.17
O.S. Fan Collets ??
I looked all the parts up at ricks and they are all in stock

I don't know what the differance is with the motor mounts. mabey some one can jump in and help with that question. I don't know if the 8.45 mounts are taller that the 8.18 and if not can the 8.45 mouns be shimed?
I hope this helps
Shawn

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08-11-2007 01:57 AM  10 years agoPost 7
T 3d

rrApprentice

Boston Mass

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gear ratio

Thanks acdnh you have been very helpful the the main question i have is my ys engine the wright mach for a 8.45 gear or is a 8.18 better for my engine and why is os better

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08-11-2007 02:08 AM  10 years agoPost 8
adcnh

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NH

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In my opinion the 8.45 is best for the YS91 and the 8.18 is best for the OS91. They is what MA recommends. I have flown both and to me and my flying style I would agree with MA with the ratio recommendations. Now as far as witch motor has more power. I we get in to that one your post will be a mile long. But i will say it any way. In my opinion OS has more power than YS but I will not take any thing away from ys they are a great running motor. I will tell you that I just took out a new YS with 4 gal thru it out of my stratus to put back in an OS 91. I have a fury with an OS-SZH that will fly circles around my stratus all day long. Hands Down. That is just my opinion. Others may disagree.

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08-11-2007 02:11 AM  10 years agoPost 9
adcnh

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NH

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P.S.
YS power curv is higher than os that is why the gearing is different
take a look at the engine spec. you will see YS is up to 17,000 rpm and OS is 16,000 thus 8.45 for ys and 8.18 for os

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11-20-2007 11:09 PM  10 years agoPost 10
txheliflyer

rrNovice

Garland, TX, USA

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Gear ratios

I'm confused. I've always read that the lower gear ratios were better for YS since the sweet spot is at a lower rpm and higher for OS. On Todd Bennett's website, freestyle3d.com, he recommends an 8.0-8.2 for the YS 91

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11-21-2007 12:31 AM  10 years agoPost 11
BJames111

rrElite Veteran

San Diego,​California

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It comes down to opinion really. The MA gearing guide is ONLY when referring to the YS91st4, if you have the NEW YS91SR, then you would be better off with the 8.18 "os" gear ratio. That being said, I flew my raptor 90 w/ 8.27 and an ST4 and liked it much better than a lower ratio.

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11-21-2007 12:50 AM  10 years agoPost 12
oldboldpilot

rrKey Veteran

Southern California

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txheliflyer,

The YS 91ST revs higher, thus the higher numerical gear ratio. 8.45 is just right for the ST engine. It is smooth, and easy to tune - and it stays tuned.

The new YS 91SR makes more power than either the current OS or YS 91's, and it does this at lower rpm than the ST. It continues to be easy to tune and to stay tuned. The Hatori "19" pipe is perfect for it. The best g.r. for the SR lies between 8.05 and 8.26 for aerobatics. 8.18 is "perfect."

OS will soon release a new 91..

Helis are Man's Defiance of the Laws of Nature - OCHC

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11-21-2007 01:09 AM  10 years agoPost 13
ddavison

rrVeteran

Brownsville,​Pennsylvania

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Maybe OS will get it right this time, for a engine out of the box without have to mod. it for power.

DaveDavison,GasGob,WhiplashGas,Spectra,JRXG11MV,12X

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11-21-2007 01:39 AM  10 years agoPost 14
txheliflyer

rrNovice

Garland, TX, USA

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Both of my X-spec's only came with a 7.91 gear ratio. I'm running them both with YS 91 ST4's. I guess with that ratio they would be more suited for F3C because to get the engine around the sweet spot of 16000rpm it would be running about 2022 head speed. BTW I could not find any documentation to verify the rpm that it makes the most hp but I have heard that through field testing 16000 was the magic number. Maybe I should order the 93T main and the 11T pinion and try it out.

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