Subaru R160 vs R180, what are the limits of each diff?

[B^2]

Right now I'm running a stock datsun diff in my 1970 510.  It's clunking a bit and I've been thinking about upgrading to either a subaru r160 or R180.  I'm thinking for now that I'd like to run a 4.11 ratio which the r180 never came in but wondering if I'm going to be limited down the road with an R160 diff if I decide to do an engine swap to something with closer to 200hp+  I'm certainly not launching my 510 or drag racing but I also don't want to worry about the rear diff being a time bomb with an engine swap down the road.  At what hp/torque do the r160 diffs start to fail, what numbers can the r180 withstand?  It seems like it would be quite expensive to get gears for an R180 diff to swap it to 4.11 so each diff comes with compromises.  Ultimate goal would be to do a cv conversion too and I'd really like to avoid buying an r160 now, just to upgrade to an R180 in a year or so.

[thisismatt]

4x4 720 use a normal long nose R180 for the front drive with 4.11 gears.

Edited November 26, 2021 by thisismatt

[datzenmike]

Only the '83 and up had the 4.11

 

 

The 510 and the Subaru R-160 are one in the same differentials made by Fuji Heavy Industries, well, the Subaru one is likely newer. I don't know who 'own' Fuji now but Nissan did own a piece of it in the past.  

 

Open differential one tire fires are what destroys them so if planning huge hp numbers get an LSD. Torque not HP determines the handling capability of a differential.

 

Take a good look at what the Subaru turbo engine puts out and how well the R-160 LSD differential holds up. 

[B^2]

I should have specified I was looking at LSD's exclusively.  

[datzenmike]

There were no R-180 LSD options. Subaru had clutch and viscous LSDs.

[thisismatt]

There were rare R180 LSD and 3rd party. Subaru has various forms of R180 LSD, but will require custom stubs or cv assemblies

[datzenmike]

I meant the car and truck R-180 didn't have factory LSD. 

 

[Icehouse]

Both the R160 and R180 use the same stub axles which seem to be one possible weak links.  So if they are both upgraded to a clutch LSD the 180 may not hold any more power.  I’ve worked on cars with over 300 HP and the R160 with a clutch LSD holds it.  Luckily for us it’s hard to launch a 510 so the diff is relatively safe.  The VLSD is junk.  Don’t bother getting one of those.  

[paradime]

icehouse is right, 510s are light, so an upgraded R160 will handle 200+ hp. Also agree the VLSD is a POS. If you'r upgrading to CVs there are options for a 3.90 ratio. The DriveShaftShop makes a CV kit with 27 spline stubs for modern Subaru diffs built in. The 2004 and 2005 Subaru STI R180 have a mechanical LSD with 3.90 ratio. That's what I'm running in my SR swopped 510 with 375 RWHP. Cruising at 65 mph its spinning about 2700 rpm. The 2008+ Subaru STI R180 is also 3.90 with Torsen LSD. Might be an expensive bit of overkill, but it's easy install with total confidence. My $.02 worth anyway.
 

[iceman510]

I believe the post-2005 Subaru STI R180 diffs are all 3.54 ratio.  They changed the transfer case ratio from 1:1 to 1.1:1, and the rear diff ratio from 3.90 to 3.54.  I have a 2005 CLSD 3.90 diff I will be putting in my 69 510.

[Z23T]

Here is a link to a good article on the various Subaru rear diffs. https://forums.nasioc.com/forums/showthread.php?t=2597453

 

[Stoffregen Motorsports]

There are easy ways to modify a stock LSD unit to gain more breakaway pressure.

 

I use a modified pair of stub axles and a dial type torque wrench with memory pointer to test breakaway pressure. I think stock breakaway is like 45 pounds, which is not enough for a car with much horsepower.