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Old 05-23-2017, 01:14 PM   #1
crazyoctopus
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Join Date: Sep 2010
Location: Oceanside, CA
Vehicle:
1972 240z

Default swap WRX ring/pinion gear in STI

I cannot find any definitive proof that it will work before I buy a diff, so I am hoping that someone can confirm this question:

Can I swap a WRX R180 (K stamp) ring/Pinion gear onto an STI R180 (K stamp) that is a clutch type?

Backstory: I purchased an STI 4.44 clutch type diff and am really annoyed at the super short gears and terrible cruising rpm on the freeway. I want to use a final drive of around 3.5-3.9 and they are most commonly found on a regular WRX. Plus, buying an open WRX diff is cheaper than a new ring/pinion set.

Also this is not going into a Subaru.
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Old 05-23-2017, 01:21 PM   #2
drewvdw
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2010 LR WRX
MPS powered.

Default

The WRX has an R160 unless that's changed with the new generation.
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Old 05-24-2017, 08:47 AM   #3
JarHarms
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06 WRX Ltd
02 Forester S

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Quote:
Originally Posted by crazyoctopus View Post
Also this is not going into a Subaru.
= 1972 240z I suspect? So no Fdiff/transfer gear/Rdiff ratio matching to consider.


I read this as you are wanting an R180 housing with a ratio of "3.5-3.9" and using a plated LSD. You already have an R180 4.444 ratio with plated LSD.
USDM Impreza/WRXs do have the ratios you are looking for but are not R180 they are R160 and those ring/pinions will not interchange. You are looking for a STI Rdiff assembly but the model year will vary depending on what you want.
STI 2004-06 R180 3.900 ratio and plated LSD
STI 2007-2014 R180 3.54 ratio and torsen LSD


*well shoot I missed that in the LSD type MY change, you're absolutely correct.
USDM STI 2004-05 R180 3.900 ratio and plated LSD
USDM STI 2006 R180 3.54 ratio and plated LSD
USDM STI 2007-2014 R180 3.54 ratio and torsen LSD

Last edited by JarHarms; 05-31-2017 at 09:14 AM. Reason: I'm getting sloppy.
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Old 05-24-2017, 02:37 PM   #4
crazyoctopus
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Location: Oceanside, CA
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1972 240z

Default

Got it, thanks for the clarification, I'll update my search terms.

If I can't find an STI diff, where do you guys go to buy just the ring and pinion gear?
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Old 05-24-2017, 09:44 PM   #5
JarHarms
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06 WRX Ltd
02 Forester S

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Subaru parts department or OEM online supply.
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Old 05-27-2017, 02:17 PM   #6
Web Foot STi
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Quote:
Originally Posted by JarHarms View Post
= 1972 240z I suspect? So no Fdiff/transfer gear/Rdiff ratio matching to consider.


I read this as you are wanting an R180 housing with a ratio of "3.5-3.9" and using a plated LSD. You already have an R180 4.444 ratio with plated LSD.
USDM Impreza/WRXs do have the ratios you are looking for but are not R180 they are R160 and those ring/pinions will not interchange. You are looking for a STI Rdiff assembly but the model year will vary depending on what you want.
STI 2004-06 R180 3.900 ratio and plated LSD
STI 2007-2014 R180 3.54 ratio and torsen LSD
One correction:
STI 2004-05 R180 3.900 ratio and plated LSD
STI 2006 R180 3.54 ratio and plated LSD

Subaru changed the center diff in '06 and the rear R/P to match.

Last edited by Web Foot STi; 05-28-2017 at 07:33 PM. Reason: Typo: Had the wrong '06 ratio. 3.54 is correct.
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Old 05-27-2017, 02:23 PM   #7
rlynch215
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Sedona Red Pearl

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What year transmission are your running? And I'm assuming that it's a 6 speed right?
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Old 05-28-2017, 11:57 AM   #8
crazyoctopus
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1972 240z

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SVO Mustang 5 speed
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