YS91 8:45 or 8:18??

[Knud Pedersen DENMARK]

My Combo:
Extreme 8.18:1, YS91, Hatori SB16FH, Revlock, SAB710. ±10°pitch(i guess)
Wildcat10%

Today I am running 1830-1860 Rpm on the mainrotor.
I guess I am running this RPM to get the YS in the Power band (15133) and because I like to Heli to react fast/crispy……but have never tried 8:45……

Would it be better to go for the 8.45:1, and lower the rpm to 1750 (remember i am suing wildcat10%) , or will 1750 make the heli less fast/crispy?

ChopperKnud

[ChrisLaFollette]

I read on Runryder where a guy was running 8.18 with the YS and he ran it at 1850 or so. He said it was really crisp which it should be and said it made a lot of power. He then switched to 8.45 and lowered the head to 1750 to get it in the powerband and said it made a world of difference. The head was much harder to bog with 8.45 and it made a lot more power. 8.45 is the preffered ratio with the Ys 91 in the Furys though and 8.18 for OS. 8.18 will give you better fuel economy but 1750 will give you that extra OOMPH.

8.45 x 1850 = 15,632

8.18 x 1850 = 15,133

8.45 x 1750 = 14,787 so at 8.18 on the YS .91 its way out of its powerband.

Like I said 8.45 is the "prefered" rpm with the YS .91s.

My math may be way off but if it is im sorry. I think its right, im not very good at math.

[BigVanVader]

Im running the 8:45 ratio on my Fury with the YS91 and MPII and it produces awesome amounts of power.....im running 1800 on my headspeed and she seems to like it,i seem to like it too.....if you watch my video from blacksheep a couple weeks ago,at the end the music stops and you can really hear the engine good...i heard it bog once very little but i think most of that was from my learning curve with the V Blades and my collective management.....those V's sure do bite the air.

[Dr.Ben]

YS91:

Full, tight 3D with lots of long or consecutive manuevers: 8.36/8.45@1750.

Sport 3D AND some preference for more open FAI style maneuvers mixed in AND/OR a desire to have some greater FF speed WITH better fuel economy than the 8.45: 8.18@1800-1825.

FAI or big, open 3D (these are becoming very similar with some of the new FAI maneuvers): 7.9:1 at 1900-2000. These numbers put the peak rpm of the engine higher, but I can tell you for an unequivocal fact that the engine and the model go like a raped ape.

Ben Minor

[Knud Pedersen DENMARK]

Hi

At what engine RPM does the YS91 (SB18FH) have the max power???

Sound like I might have to try the 8:45/1750 option..........

ChopperKnud

[DavidH]

Knud,
YS 91
at 8.45 and 1750 on the rotor head. Your right in the heart of the power band at 14,700 rpms. With 8.45 and the YS 91 I would suggest not running the head speed any higher than 1800.

As Ben suggested. 8.36 would be great also if you want to run the head speed just a little higher than 1750.

Here is the RPM specifications for the YS 91
Specifications

RPM Range: 2,500 to 15,000 RPM
The above Specs are from YS Performance. These guys are very knowledgeable about YS engines.

From the YS 91 instructions

You should be using an engine to main rotor gear ratio of
1-7.5 to 1-8.0. Please check with your helicopter
manufacturer to obtain the correct gear ratio.

David

[Knud Pedersen DENMARK]

Okay – I think i´m going to try the 8.45…….

What parts number do I need to convert my 8.18 to 8.45?
Can I use the same engine mount?

I do not need the engine-shims for 8.45 – do I???


ChopperKnud

[DavidH]

On the Extreme you will need the 8.45 motor mounts
119- 50 and 51 I believe is the numbers.
You will need the 8.45 clutch plates.
93 tooth main gear.

If you decide to do 8.36. Only difference is 92 tooth main gear.

No shims required for 8.45 mounts.

David

[TonyM]

Can just jump on and ask about the engine mounts.

I was told that the mounts (818 845) are the same and its just the 818 needs motor shims.
So, this is not the case?
What are the physical differences between the 2 mounts?

I recently went from 818 to 845 with my YS/ hatori combo (yes, much better for tight 3d) all i changed was the main gear and carbon plates. i also removed the brass shims from under the motor lugs.

Thanks

[DavidH]

The 8.45 motor mounts 119-50 and 51. And the 8.18 mounts 115-50 and 51 are basically the same.

The 8.45 mounts have .030 milled off the face of them to accomodate the clearance needed for the 8.45 ratio.

You can not use 8.18 mounts on an 8.45 ratio.
You could use 8.45 mounts on an 8.18 ratio, but it would require .030 in shims on each side.

If you went from 8.18 to 8.45 and did not change the mounts. Then the mounts that were in the heli were the 8.45 mounts. With the 8.18 mounts and 8.18 ratio, no shims is used.

David

[TonyM]

perfect, thanks for clearing that up

[Knud Pedersen DENMARK]

Hi
Can I use the same pinion (11 tooth i thnk) on the clutch, from the originale 8.18:1 ratio if changing to 8.36 or 8.45

What would be the prefered rotor RPM on 8.36 YS/SB16FH - 1750-1800 ??

Is there a big performance difference between 8.45 and 8.36???
I strongly consider going for the 8.36 at first – because it is cheaper to make the change.
------------------------------------------------
DavidH
With the 8.18 mounts and 8.18 ratio, no shims is used

On the picture in manual there is written “#115-47 8,18:1 only” (See my gallery)

I have Shims under the YS91 with 8,18:1 gearing, and I guess the engine mount is 115-50/51……..
----------------------------------------------------
DavidH
The 8.45 mounts have .030 milled off the face of them to accomodate the clearance needed for the 8.45 ratio.


How much is that in Millimetre???
To safe some money, I could milled of the 0,030 (inch??) /XX mm.
--------------------------------------------------------------



:mrgreen:
ChopperKnud

[DavidH]

I have Shims under the YS91 with 8,18:1 gearing, and I guess the engine mount is 115-50/51……..


Knud,
Sorry I was confused. It is difficult to keep up with the different shim combos at times.
8.18 ratio = 115-50 & 51 mounts. One 115-47 shim ( 0.30) shim on each side.

If you used the 8.45 mounts 119-50 &51 on the 8.18 ratio. You would need two 115-47 shims on each side for a total of 0.60 thickness in shims.

For 8.36 ratio. A rotor head speed of 1750 - 1800 would still be an idea range.

I strongly consider going for the 8.36 at first – because it is cheaper to make the change

Changing to 8.36 will not be any less expensive.
You will still need
92 tooth main gear
119- 50 & 51 motor mounts
8.36/8.45 clutch plates.

David

[Knud Pedersen DENMARK]

Hi DavidH

Thank´s for the quick answars :-)

Do you know how much 0,03 difference bewteen the enginemount, is in Millimetre???

ChopperKnud

[DavidH]

Here is a great site for conversions

http://www.projects.ex.ac.uk/trol/scol/index.htm

0.03 = 0.762mm

David

[Knud Pedersen DENMARK]

hi DavidH

Oh yes now I remeber: I think you have giving my this Conversion link before :arggg:

Thank´s

ChopperKnud :smokin:

[Knud Pedersen DENMARK]

The 0,03 inch (0,76mm), is that the same mesh as the Engine-shims #115-45???

ChopperKnud

[DavidH]

Yes, the 115-47 shims are 0.030 thick, which would be 0.762mm.

David

[Knud Pedersen DENMARK]

Cool – then I can milled off 0,762 mm on the old engine mount – and then save some money, for more heli- parts :lol: :lol:

ChopperKnud :cool:

[Knud Pedersen DENMARK]

Hi

Just for your information.
I have now changed and flow with the new gearing 8.45:1.

I did buy a new engine mount (119-50 + 119-51) - But it was not necessary – I measured the new and my old engine mount, and there was no different….
Afterwards I looked in my manual :arggg: , and could read that my Extreme 8.18 was “born” with these engine mount (119-50/51) + shims 115-47 (8.18:1)………so now a hove some spare mounts :-)

BUT:
The gearing seems to rock and pleasure the YS a lot. :glasses2: :D
I run about 1760-1800 in idlup 2.
The engine does not bog down as easily in ex. Tic tac – where the problems seems to be to much stick banging (Still on wildcat 10%)

Now there is only a tail waggle (swing aproxx 4-8° to the side) when shifting pitch in Tic tac´s…

BTW: I did try a tank full Wildcat CY: and there it almost didn’t bogging down in rpm – not even if I did much pitch pumping – but it is a high coct fuel…….maybe I will go for the Wildcat 30%
:?:

ChopperKnud