OS Giken R154 - 5th gear ratio change?

[Supra56]

Gidday Guys,
I have a race car with 7m 540rwhp, with a R154 with Os Giken gear
set.
I was wondering if anyone makes a lower(shorter) 5th gear to suit.
Standard 5th gear is .753, I would like around .85, or lower again if possible.

I don't want to lower the diff ratio or tyre/wheel size, otherwise the car will be inbetween
gears around corners, as currently the other ratios are perfect, it just when I get
to the straights that the car feels like it die's when I select 5th.

Currently speeds in the gears
1st 85km/h @7000rpm
2nd 142
3rd 189
4th 229
5th 304 km/h.
As can be seen the gap from 4 to 5 gear is very big. 75km/h (47mph)
Thanks

 

[bioskyline]

as the OS Giken gear sets are discontinued, your probably out of luck. only option i can see is have a custom made gear from a shop that specializes in transmissions.

there is this that MAY work. http://en.wikipedia.org/wiki/Toyota_R_transmission this is all the R-series trans that toyota makes. the R150f found in most toyota trucks has 5th gear of 0.838:1, maybe it will work in the r154, with some machineing work and mods to both gear and tranny, and would be close to what you need. im not a tranny expert, but might be worth asking someone

good luck

 

[Supra56]

Thanks, I will look into that.