fitting a LSD diff in a cosmo

[kiwiJC]

hi, i am trying to find out if any one has fitted a non cosmo LSD unit to their diff.
if i understand right the standard cosmo one is a viscous unit which is unserviceable and good for nothing after 100,000 km?
i have read what doesnt fit. but if any one knows what might fit even with a little bit of machining.
any info is better than none.

 

[rodneooo]

i have been trying to figure out the same thing for years....
except i have a 13b, which will be even more hard to figure out.
im thinking about giving my spare diff to a place and let them fiugure out something.

 

[rodneooo]

do u have the std 13b lsd?
or 20b?

 

[kiwiJC]

i have a open 13b diff, there is one or two 20b lsd diffs that i can get, but my car is a manual now and the 20b diff makes the gearing very high. so i intend to fit the lsd to a 13b diff. does any one know how different the rx7 ones are?

 

[rodneooo]

let me know if u find out anything.

theres a bloke on ausrotary who is a diff specialist.
In the not too distant future i might send the center over to him and see what he can do to get me an lsd.
and tell him
i want it to be a direct swap, bolt in
i want to keep my std 4.11 ratio

and just see what he comes up with.

 

[rodneooo]

Hi not too sure if u have figured it out yet, but i was imformed by a diff specialist that the fd lsd fits inside a cosmo 13b open center. i havent confirmed for my self as yet. but he did do a test fit and sold me the lsd. he is a respectable diff specialist from ausrotory.

 

[pjman]

Hi not too sure if u have figured it out yet, but i was imformed by a diff specialist that the fd lsd fits inside a cosmo 13b open center. i havent confirmed for my self as yet. but he did do a test fit and sold me the lsd. he is a respectable diff specialist from ausrotory.

Thats some handy info right there!!!!!

 

[rodneooo]

yeah i kinda figured that would be the case, but i had to know for sure before forking out. BTW he didnt test any other cosmo diffs, but he reckons 20b is different, and 13b lsd has different shafts but the open center 13b diff is beaut for the fd lsd.
i ended up getting a 2nd hand mazdaspeed 2 way off him. i cant wait to chuck it in.

 

[13bcosmo]

thats awesome whats the rx7 ratio? are you sure the standard open is 4.11??

I recently purchased a cosmo diff and it's a torsional 4.3 so they come in two sorts. haven't installed it yet.

 

[Rotorzilla]

i have a open 13b diff, there is one or two 20b lsd diffs that i can get, but my car is a manual now and the 20b diff makes the gearing very high. so i intend to fit the lsd to a 13b diff. does any one know how different the rx7 ones are?

I converted my Cosmo to 5 speed using a FC trans
1st 3.48
2nd 2.02
3rd 1.39
4th 1.00
5th 0.72

tire size 18 255 40

using the calc on this page I set rpm to 7500
http://www.boosttown.com/gearbox_differential/speed_calculator.php

road speed @ 7500
rear ratio 4.3 ( 13b cosmo)
1st Gear = 62.43 km/h
2nd Gear = 107.56 km/h
3rd Gear = 156.31 km/h
4th Gear = 217.27 km/h
5th Gear = 301.77 km/h

road speed @ 7500
rear ratio 3.9 ( 20b cosmo)
1st Gear = 68.84 km/h
2nd Gear = 118.59 km/h
3rd Gear = 172.34 km/h
4th Gear = 239.56 km/h
5th Gear = 332.72 km/h


The stock Cosmo 4 speed auto trans had a .694 final gear. I was wondering if anyone makes FC 5th gear in .69 I would like to get my highway cruisng rpm down. right now 100km is like 2800 rpm I would like to drop it down to around 2000 rpm like the stock cosmo ran.

the stock cosmo speeds are
rear ratio 3.909 ( 20b cosmo)

1st Gear = 85.85 km/h 2.784
2nd Gear = 154.8 km/h 1.544
3rd Gear = 239.01 km/h 1.000
4th Gear = 344.39 km/h 0.694

 

[rodneooo]

Im not sure about the fd, but the cosmo isw 4.3. Sorry i had abit of a mix up back then.

 

[Rotorzilla]

I wounder if you can put 4.1 from a FD into a Comso. That would give a little better on the highway but not much more different in the other gears

 

[kiwiJC]

lots of good info there. my flat mate just happens to have a FD that he races and there are a few spare diffs laying around. ill have to try fitting one.