Subaru STi R180 Option from FutoFab

Engine, Transmission and related drivetrain.
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Dave Patten
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Subaru STi R180 Option from FutoFab

Postby Dave Patten » 10 Nov 2015 09:27

It was brought to my attention that there may be a lack of concise information about using a late model Subaru STi R180 differential in a Datsun.

Let me try to clear this up somewhat and try to get everything in one place.

First you need to source a 2004-2015 Subaru WRX STi differential. It MUST be an STi model to work, the standard WRX or any other Subi R180 diff will not. The years/ratios/LSD type are below (this info is to he best of my knowledge).

Subaru WRX STi R180 rear differentials (US Market):

‘04 & ’05 - 3.90 ratio Clutch type LSD
‘06 - 3.545 ratio Clutch type LSD
’07 to ’15 - 3.545 ratio Torsen LSD

Next you need a set of conversion stub axles. These are designed to mate the STi differential to the Datsun half shafts. The conversion stub axles were originally sold by Beta Motorsports, then by Wolf Creek Racing (WCR) and now with our acquisition of WCR they are a FutoFab product.

Before installing the new conversion stub axles, you will need to remove the Datsun stub axles and swap the serrated shoulder studs from the Datsun stub axles into the conversion stub axles. It is my understanding that these studs are NLA from Nissan and if ordered from the dealer, they will be a standard hex head bolt.

The Subi STi R180 uses a c-clip retainer to hold the stub axle into the diff. The conversion stub axles have 27 splines to mate with the STi diff. Nissan stub axles, even if c-clip retained will not work as they are either 25 or 29 spline. The conversion stub axles also have the needed 4 bolt flange to fit the Datsun half shaft, allowing the half shafts to bolt directly to the STi R180 diff.

To connect the Datsun drive shaft to the STi diff, you will need to swap the input flange from the original Datsun diff onto the STi one. These are a direct swap, undo the pinion nut and swap the flanges. The nut may be staked onto the thread of the pinion shaft. The staked area must be ground away before the nut is removed, otherwise the thread will be damaged and reuse of the diff will likely be impossible.

Kurt Hafer did a pictorial of the swap with narrative descriptions of each picture. Link to the album - http://datsun510.com/showgallery.php?cat=3700

The Subaru STi R180 conversion stub axles can be purchased from FutoFab for $500/pair + S&H. Please contact me at FutoFab@gsinet.net

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Dave Patten
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Re: Subaru STi R180 Option from FutoFab

Postby Sleepys-14 » 10 Nov 2015 10:37

I have the same setup and it works fantastic! Track approved.
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Re: Subaru STi R180 Option from FutoFab

Postby PoorMtnKid » 10 Nov 2015 10:44

Awesome that you are taking over the production of the stubs. Good to know!
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Re: Subaru STi R180 Option from FutoFab

Postby iceman510 » 10 Nov 2015 18:20

Dave, do these also work with the CV conversion axles? You should possibly consider a bundling price to be competitive with other offerings.

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Re: Subaru STi R180 Option from FutoFab

Postby tr6racer21 » 10 Nov 2015 18:41

Thanks Dave this is great info.

Wanted to add a little about the clutch style diff. I am using the STi R180 in my Vintage track car. After/during initial installation I noted how easily the axles seemed to break loose from one another. The performance of the car suffered during the weekend at the track. When I came home from the weekend I called David Anton at Rallispec and ordered a new clutch pack for the diff. With a combination of various mix and match clutches I was able to get my break-away torque up to about 100 ft/lbs. I can look up the combination if anyone is interested. I believe the directions that come in the kit are in Japanese, but the pictures are self explanatory and David may also have some additional info from what they used in their rally prep cars.

From their website "Is the factory R180 clutch type LSD ready to be used in competition or does it require modification? The factory R180 clutch type LSD used on certain Impreza STI models is set up with very low initial torque in order to minimize noise. It will not be very effective in most competitive applications and will wear quickly due to high relative rotation between the friction surfaces. Rebuilding the LSD with RST-1951RK for higher initial torque will make the LSD more effective for a wide range of competition purposes. However, there will be a noticeable increase in noise due to stick-slip phenomenon while cornering with no or light throttle input. Careful oil selection can help reduce noise levels somewhat."

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Re: Subaru STi R180 Option from FutoFab

Postby Sleepys-14 » 12 Nov 2015 07:26

TR6- I noticed the light breakaway torque also. It is very light at about 15-20lbs. Although I though this would be an issue, it actually works very well for me with the light breakaway. I have never had any in-lift or unlocking of the diff while under part or full throttle at any point in time. Which leads me to believe that the ramp rate is well designed for the light break away torque. A light breakaway helps to tame the rear end a bit especially on and off throttle inputs mid corner.
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Re: Subaru STi R180 Option from FutoFab

Postby 510wizard » 12 Nov 2015 07:38

A question, are the stub axles the same between the clutch type and the Torsen type ? I thought I read some ware that the Torsen type were longer.

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Re: Subaru STi R180 Option from FutoFab

Postby Byron510 » 12 Nov 2015 07:58

On the subject of breakaway torque;

With the use of street tires, even DOT R compounds, I have found that at 60 lbs the diff is basically spool or locked diff. It’s likely a different story with race rubber on a warm track. I dropped mine from 90 to 60, and then to around 40lbs (43 I believe) before I was happy with the diff. In fact it's stiff enough that when I take the R compounds off, the diff will still chatter the Yoko S drives when the drivetrain is cold at low speeds on sharper corners like in parking lots and RH turns.

Just my experiences to share with the group.

On the subject of the Torsion; I’ve always wanted to try a torsion diff, because it was all the rage 20 years ago, and now is a common unit in many cars. That’s on the one day list.

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Re: Subaru STi R180 Option from FutoFab

Postby iceman510 » 12 Nov 2015 09:14

Good info on the torque. I just recently acquired an '05 STI diff I hope to implement next year (with the CVs too).

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Re: Subaru STi R180 Option from FutoFab

Postby bertvorgon » 12 Nov 2015 13:12

Just to add my experience, at least with the Nissan LSD in my R180, that I used about 45 lbs with my race slicks and have not touched anything since.
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Re: Subaru STi R180 Option from FutoFab

Postby zKars » 14 Nov 2015 06:29

this is wonderful and very useful information. Now if there was an easier way to actually find these Subie diff's then we'd have a powerful tool. Anyone who has a favorite source company or method, please let us all know! I'm in the market to swap my Z31 R200 CLSD and CV's for a 3.90 Subie diff the above stubs and Porsche style CV's in my Z.

And then I looked further down the list of recent posts and see my local buddy 2doorJim is also looking of a subie diff. We need a pair, someone come to our rescue!

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Re: Subaru STi R180 Option from FutoFab

Postby SteveEdmonton » 14 Nov 2015 17:18

If the price isn't too crazy I might be in the hunt as well-- that would make a 3-pack for Alberta, you two guys in Calgary and me up here in Edmonton!

At some point do you think we could ask for a volume discount? :wink:
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Re: Subaru STi R180 Option from FutoFab

Postby iceman510 » 14 Nov 2015 18:10

I bought mine from a guy on NASIOC. I am not a member there, but utilized a friend that was to pm the guy after searching the classifieds.

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Re: Subaru STi R180 Option from FutoFab

Postby Dave Patten » 17 Nov 2015 19:37

A question, are the stub axles the same between the clutch type and the Torsen type ? I thought I read some ware that the Torsen type were longer.


CLSD or Torsen are the stub axles.

Dave, do these also work with the CV conversion axles?


Yes, the WCR CV Axles will work with the stub axles.
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Re: Subaru STi R180 Option from FutoFab

Postby 510wizard » 18 Nov 2015 07:38

Dave Patten wrote:
A question, are the stub axles the same between the clutch type and the Torsen type ? I thought I read some ware that the Torsen type were longer.


CLSD or Torsen are the stub axles.

???
Dave, not sure I understand your answer. Let me rephase the question, is the length of the spline/shaft portion the same between the torsen vs the clutch type? I thought the torsen needed a longer spline/shaft to engage into the lsd portion.


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