What gear ratio for YS91?

[bob7657]

What gear ratio are the FAI folks running with YS91 and tempest FAI model?

Is anybody running a fun tech muffler and your opinion?

Also I saw a YS91 STR, anybody know what this is, could not find it on the YS website or any info?

David you out there?

[bighands3d]

I know that most are using the 8.45 with the Hatori SB 16 HS 1750rpm and the 8.18 with the MPII HS 1850rpm

Not sure about your muffler setup. Who sells the funtech and what does it look like.

[DavidH]

Bob,
The Tempest FAI kit should come with 7.75 ratio. That will work fine with YS 91. Also 7.91 is available, I have not tried it. To go from 7.75 to 7.91, all you change is the clutch plates and go from 93 tooth main gear to 95 tooth main gear.
The motor mounts will accept the change with only a shim removal.
The Fun Tech muffler will work nicely. You should be able to get one from James at OMI.
The STR is a 91 that has an anodized red head on it. I don't know of any other differences in the motor.

David

[bob7657]

Thanks for all the info, much help and appreciated! :-)

[bighands3d]

I didn't know they came with that low of a ratio Dave... I guess you learn a little every day.

I guess thats what you need for the FAI stuff.. Didn't even know they made the ratio's that low for the MA stuff.

[DavidH]

The Tempest can be set for ratios from 7.5 to 1 up to 9.5 to 1 at this time.
Here are the available ratios for the Tempest
7.5 to 1 90/12
7.66 to 1 92/12
7.75 to 1 93/12
7.91 to 1 95/12
8.18 to 1 90/11
8.36 to 1 92/11
8.45 to 1 93/11
9 to 1 90/10
9.2 to 1 92/10
9.3 to 1 93/10
9.5 to 1 95/10

I believe that is all the gear ratios are currently capable on the Tempest. The Spectra will offer even more ratios available.


David
9.5
8.45 to 1 93/11