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Century Helicopter . MTA Hobbies . Model Rectifier Corp

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Engines Plugs Mufflers Fuel > YS 91 SR - YS 91 ST4 differences
 
 
GEORGE GR
Heliman
Location: Greece

hello,

i am interesting to buy a YS 91 engine for my heli.
Could you anyone, tell me please, which is the difference between the
YS 91 SR long stroke and YS 91 ST4 ?

Thanks
George
07-31-2008 04:33 PM
 
 
DS 8717
rrProfessor
Location: Here wishing i was somewhere else

The SR has a longer stroke,smaller bore.The bore in the SR carb is .5mm larger than the ST. The bearings now have plastic retainers instead of metal ones that rust.
07-31-2008 04:53 PM
 
 
BJames111
Elite Veteran
Location: Billings, Montana

also the appropriate g/r is a bit different. The SR doesn't rev quite as high as the ST. It does have a touch more torque though, and is happy on 8.18 (in my machine).

Brian James
Miniature Aircraft Fury Extreme
G-Force Heli
Elevated R/C
07-31-2008 08:24 PM
HOMEPAGE  
 
 
GEORGE GR
Heliman
Location: Greece

hello again,
which of the two engines, would you buy today?
07-31-2008 10:31 PM
 
 
Droid
Elite Veteran
Location: Deep down in the Southwest- UK

Quote 
which of the two engines, would you buy today?

Depends what machine you intend using it in and what sort of headspeed you are looking for. The 91 SR loves the lower gear ratios(less than 8.27 to 1) and gives loads of torque. If you are after higher headspeeds and have 8.27 and above then the ST is the better choice.

Both are great engines, the SR is definately more torquey and probably has slightly better spares support at the moment.

Quotes may have been changed for my own amusement
07-31-2008 11:54 PM
 
 
ErichF
Key Veteran
Location: Odessa, FL 33556 (Tampa Area)

I think that decision has been made for you...I don't believe you can purchase the 91ST4, unless it's used or old stock.


Erich

Team Kyosho Regional Field Representative
08-01-2008 01:50 AM
 
 
Droid
Elite Veteran
Location: Deep down in the Southwest- UK

ST4's are still avavilable, if you look hard enough.

Quotes may have been changed for my own amusement
08-01-2008 08:16 AM
 
 
Henrik Engert
Key Veteran
Location: Cedar Park, TX

What's a ST4? I think it is just a ST plain and simple, at least that's what it says on the box...

Hirobo XSpec EVO
Futaba 12Z FASST
08-01-2008 01:36 PM
 
 
ErichF
Key Veteran
Location: Odessa, FL 33556 (Tampa Area)

YS 61ST
YS 61ST2
YS 80ST(3)
YS 91ST4

I think it says ST4 on the case, but I can't remember.

Team Kyosho Regional Field Representative
08-01-2008 02:01 PM
 
 
Dood
Elite Veteran
Location: America's Dairyland

Quote 
I think it says ST4 on the case,

yep

(\__/)
(='.'=) The Dood abides.
(")_(")
08-01-2008 02:04 PM
HOMEPAGE  
 
 
Henrik Engert
Key Veteran
Location: Cedar Park, TX

I have to look closer, but don't remember seeing it. I have only looked in the manual, and there it says ST...

Hirobo XSpec EVO
Futaba 12Z FASST
08-01-2008 03:03 PM
 
 
DS 8717
rrProfessor
Location: Here wishing i was somewhere else

Theres no ST 4 on the motor,the box or the manual.
08-01-2008 03:09 PM
 
 
Henrik Engert
Key Veteran
Location: Cedar Park, TX

Quote 
Theres no ST 4 on the motor,the box or the manual.

Just what I thought

Sorry for my interruption on this subject

Hirobo XSpec EVO
Futaba 12Z FASST
08-01-2008 03:54 PM
 
 
Dood
Elite Veteran
Location: America's Dairyland

Quote 
Theres no ST 4 on the motor,the box or the manual.

maybe Not on yours, but mine had an "ST4" on the mounting tab (muffler side).

(\__/)
(='.'=) The Dood abides.
(")_(")
08-01-2008 04:20 PM
HOMEPAGE  
 
 
ErichF
Key Veteran
Location: Odessa, FL 33556 (Tampa Area)

Yeah, mine too, all three of em.


Anyway, who gives a chit?

Erich

Team Kyosho Regional Field Representative
08-01-2008 05:14 PM
 
 
Dr.Ben
Elite Veteran
Location: Richmond, VA, USA

I'd be interested to see a pick of the ST4 imprint on an engine. I've seen at least six examples, none of which had the imprint on the engine or the packaging.

The 91ST is still quite popular in Japan, preferred by some over the SR.

Ben Minor
08-01-2008 06:08 PM
 
 
Henrik Engert
Key Veteran
Location: Cedar Park, TX

Quote 
Anyway, who gives a chit?

I'm just curious, that's all. I keep reading about this ST4 engine.

Hirobo XSpec EVO
Futaba 12Z FASST
08-01-2008 06:11 PM
 
 
GEORGE GR
Heliman
Location: Greece

hello,

thanks for the replies,

i am interesting to buy the YS 91 for my x-cell pro 2k with gear ratio
7.75 to 1
Probably i will buy the YS 91 SR.

George
08-01-2008 07:52 PM
 
 
ErichF
Key Veteran
Location: Odessa, FL 33556 (Tampa Area)

OK, since this was quietly eating at my brain all day, once I got home, I yanked the canopy off the Caliber and looked...

I was right that there is a 91ST printed on the mount tab, but no 4

Don't ya hate it when your mind plays tricks on ya?

Erich

Team Kyosho Regional Field Representative
08-01-2008 10:42 PM
 
 
Henrik Engert
Key Veteran
Location: Cedar Park, TX

Quote 
OK, since this was quietly eating at my brain all day, once I got home, I yanked the canopy off the Caliber and looked...

I am sorry Erich, I am just trying to get you thinking about something else than F3C

Hirobo XSpec EVO
Futaba 12Z FASST
08-01-2008 11:23 PM
 
 
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Engines Plugs Mufflers Fuel > YS 91 SR - YS 91 ST4 differences
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