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12-20-2003 04:43 PM  13 years agoPost 1
bart

rrNovice

Ripon, CA

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Hey guys,

Just wondering if you guys are using the big fans with the 90 motors. I don't know if they are necessary and I'd rather use the stock fan setup.

I might be ignorant here, but it seems to me that a 90 motor wouldn't be working as hard as a 60 in the same application, therefore wouldn't need any additional cooling. Engine block size, cooling fin size, and motor rpm are all about the same right ? Just my logic, I could be way off!

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12-20-2003 07:17 PM  13 years agoPost 2
MJA

rrKey Veteran

UK

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I use the bigger fan on MIllenium and Futura
for the reason that it'll allow me to run a little leaner
on the needles,which gives better fuel economy,but not by a massive amount or should i say as much as you'd expect for the difference in fan sizes.Probably because the 91's rev less on average so fan doesn't shift as much air as same fan with 61 in it.
It's far more
important to always use a close fitting shroud with a baffle piece in
over the top finning when necessary.I left a massive gap once over the top of the finning and it overheated unless left quite rich

The cooling requirement is about the same for both engines ,61 and 90,if anything the 90 needs more,at least when comparing OS's,
61SX to 91SX .I only say this because the OS91SXH (non C -spec) had to be run richer in my Millenium and Raptor than an OS61SXH.
The reason i think is although the 61 revs higher,the older 91 had a smaller cylinder head and produces about 1/2 HP more.The by product of that power is usually extra heat generated.


Martin

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12-21-2003 12:20 AM  13 years agoPost 3
tim tompkins

rrVeteran

Boston, Georgia sw Ga. Thomas County

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fan size

I use the Y/S 80 in my Nova and in one of my SE's.In the worst conditions possible here,95 + temp and at least that in realitive humidity I never have an overheating issue with the smaller fan.Now the new kits come with the larger fan.I would use one as a replacement if it were wrecked or broken,but I would not go to the trouble of changing unless it was.I also have a lot of fun with my Y/S 61 stII powered SE.It runs @ a higher engine speed,9.23 ratio not the 8.18 I use in the others.It is more likely to get near overheating than the others.I run a lot of CP-30 through them and I think thats the key,lots of fuel. TimT

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12-21-2003 03:31 PM  13 years agoPost 4
Ron Cosby

rrApprentice

Shreveport, Louisiana

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I ran my YS91 this summer on many 90-95 degree afternoons with no trouble. That's with the stock fan, %30 nitro.

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12-21-2003 03:54 PM  13 years agoPost 5
MJA

rrKey Veteran

UK

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Good points about the nitro,i use 10% nitro so i can't fuel cool OS's as much as with 30% by leaving a richer mixture.Fortunately Robbe heli's have a good cooling setup to begin with.

Apart from the bigger fan diameter,the alloy version of the D90 fan has curved blades which are generally regarded as more efficient because you are increasing the effective length of the blades in the same limited space between two circumference lines out from centre .The plastic D90 fan looks a bit crappy to me,most likely only gain is the increase in diameter to compensate for a lower revving 90 motor.


Martin

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12-21-2003 03:57 PM  13 years agoPost 6
bart

rrNovice

Ripon, CA

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thanks guys

I think what I'll do is just run the stock setup for now, then change it over after I crash it, or change it once the weather starts getting too hot.
We have have a good 3 to 4 months left of cold weather...I love how these motors run on cold days! Just as long as my fingers don't get numb and I can't feel the sticks anymore.

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12-22-2003 07:32 PM  13 years agoPost 7
toppo

rrApprentice

england LEICESTER

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can u tell me wat the part number is for the bigger fan,ive got a futura se with a webra 61 init and i need a new fan anyway so i will just go with a bigger one ?? this os my winter project and im just getting a robbe scale fuse for it im going for a royal,,,has any 1 fitted one of these before or got any pics of one dun thanks all mark

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12-22-2003 10:13 PM  13 years agoPost 8
Futurac

rrKey Veteran

Belgium , Europe

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Fan

S4870 for Plastic
S4129 Alu fan

Alex (Formerly Known as RCMarket )

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12-23-2003 09:55 AM  13 years agoPost 9
Andi G

rrVeteran

Switzerland

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Hi,

don't forget the D90 fan shroud (S4875). The S4870 fan won't fit in the older shroud.

Andi

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