Kawasaki F5 / F8 / F9 Close Ratio 5th gear
The stock 5 speed transmission of the Kawasaki F5/F8/F9 is actually a close ratio 4 speed transmission with a very tall and distant 5th gear ratio. In the past, the best close ratio option was to install the F81M gearbox. As time has gone on, these F81M gearboxes have become very rare (and expensive). To attend to this problem, we have embarked on “fixing” the 5th gear issue of the stock gearbox…. And that fix is not complex.
The H1 triple 5th gear-set installs easily into the Bighorn gearbox, and it offers a ratio that turns the stock Bighorn gearbox into a “close-ratio” box. The problem is that the stock Bighorn 1st gear (driven-shaft) that engages this H1 5th gear has the wrong shift-dog pattern.
We are in the process of manufacturing a custom batch of the Bighorn 1st gear that will allow the use of the H1 5th gear. The ratios (compared to the F81M gearbox) are shown below.
GEAR F9-H1-5th F81m
1st 2.45 2.45
2nd 1.71 1.60
3rd 1.17 1.26
4th .90 1.09
5th .81 .95
As the chart shows, the 4th and 5th ratios of the H1 modified F9 box are “very” close to one another….. but that is ideal for high geared pavement engine arrangement.
The H1 5th gear set are all the same (among different years), and readily available worldwide. We will be offering the modified 1st driven-shaft gear to mesh the H1 5th gearset for $219. each (plus freight). There are a limited number available, so a $100 deposit will secure the gear until delivery around May 1st. If you change your mind after deposit, we will gladly refund you. At this time
(3/13/18) only 4 are still available.
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