What common, cheap, lightweight IRS diff?

What common, cheap, lightweight, IRS diff has a bunch of ratios?

Oh yeah about 200 ft-lb capable.

I was thinking Miata, but that doesn't seem to have a bunch of ratios (just the two 4.* and the automatic 3.9)

I was thinking solstice but I don't think they are light and they aren't findable.

toyota 4 runner? but all I find is rock crawler ratios (especially for the front)

Ford 7.5" but that isn't IRS.

Help me where I am wrong and correct me where needed.

Help GRM, you are my only hope.

I imagine that the BMW 3 series diff from the the e36 are likely a good option. Might be a little heavier than the miata but not any different than the Toyota. There aren't a ton but a good source will be locostusa.com.

Ford 7.5" was available in the Tbird/cougar with IRS and has tons of cheap options. Iron case though so an AL case 8.8" is similar weight. The 7.5" is cheaper.

mazda rx7 IRS diffs have quite a few options I think.

There is the r200 that I believe comes in subarus and nissans (different cases but the gearsets I think are interchangeable).

BMW has a ton of diffs and a ton of ratios across models and years and manual vs. auto.

singleslammer wrote: I imagine that the BMW 3 series diff from the the e36 are likely a good option. Might be a little heavier than the miata but not any different than the Toyota. There aren't a ton but a good source will be locostusa.com. Ford 7.5" was available in the Tbird/cougar with IRS and has tons of cheap options. Iron case though so an AL case 8.8" is similar weight. The 7.5" is cheaper.

e36 has basically anything you want from 2.93 to 4.44. http://www.bokchoys.com/differential/GearRatios.htm

but I THINK there are two different size of ring gear going on there. BMW had generally 3 sizes of diff across all models during those years, and e36 would either have small or medium depending on engine.

In reply to Robbie:

Yeah, BMW has one for just about every possible ratio you could want - and they will take a lot more than 200 ft/lbs too. Mounting the earlier trailing arm car cases can sometimes be a hassle - but often you can swap the rear cover to an E36 style "2 ear" to make it work.

Flight Service wrote: I was thinking Miata, but that doesn't seem to have a bunch of ratios (just the two 4.** and the automatic 3.9*)

There are many other ratios, but yeah, probably not 'cheap' as they won't be found in the junkyard.

R160/R180/R200?

The Subaru/Nissan r200 diff (made by Fuji heavy industries) has many options, all of them are very expensive. Because it's "JDM yo!"

For a very inexpensive option, go ford 8.8. They came IRS in thunderbirds, all you need is the housing, everything else swaps in from explorer and mustang parts. You can rebuild the LSD for about 200$. The gearing ranges from ultra low mustang v8 stuff to crazy high off-roader exploder stuffs.

BMW "medium case" diffs are the winner as mentioned.

E28/E24/E30/E36 (the 4 cyl E30/E36 have the undesirable "small case" diff)

z31maniac wrote: (the 4 cyl E30/E36 have the undesirable "small case" diff)

Which I saw a friend put 500whp through from a boosted S52 shoved in an E36 318 Diff eventually failed, but it took a while (and the replacement lasted until the car was totaled).

Is300 lsds are available in 3.9 and 3.7 for around $400. They're tough too. I have a spare open 3.73

Trackmouse wrote: The Subaru/Nissan r200 diff (made by Fuji heavy industries) has many options, all of them are very expensive. Because it's "JDM yo!"

Not sure on the ratio selection, but even the most picked over Subarus in the pick and pull often have the rear diff left behind.

You might try Cadillac. I remember that they had some unusual ratios. Not too sure about LSD though.

The r200 has a lot of selections for ratios but its not what I would call light.

What about an MN12 IRS? (8.8 or 7.5).

Trackmouse wrote: The Subaru/Nissan r200 diff (made by Fuji heavy industries) has many options, all of them are very expensive. Because it's "JDM yo!"

Trackmouse wrote: For a very inexpensive option, go ford 8.8. They came IRS in thunderbirds, all you need is the housing, everything else swaps in from explorer and mustang parts. You can rebuild the LSD for about 200$. The gearing ranges from ultra low mustang v8 stuff to crazy high off-roader exploder stuffs.

2002-2006 Ford Explorers and all the Mercury/Lincoln variants also have aluminum case 8.8s. I'm putting one in my RX7 as we speak.

Apparently the 2007-2010 Explorer diff is the one I want. 8.8, the lightest of the 8.8 IRS bunch, as it is all aluminum and is cheap from pull apart.

The difference in the 02-06 and the 07-10 is the ribs, rear housing and mounting points on the front of the diff.

Apparently a 07-10 2 points near the carrier bearing to attach to the chassis (good) and monster wings on the housing and fewer ribs (Ok for more attachment, bad on the less ribs)

See this is why you guys are awesome.

rslifkin wrote:

z31maniac wrote: (the 4 cyl E30/E36 have the undesirable "small case" diff)

Which I saw a friend put 500whp through from a boosted S52 shoved in an E36 318 Diff eventually failed, but it took a while (and the replacement lasted until the car was totaled).

Two weeks later?

jstein77 wrote:

rslifkin wrote:

z31maniac wrote: (the 4 cyl E30/E36 have the undesirable "small case" diff)

Which I saw a friend put 500whp through from a boosted S52 shoved in an E36 318 Diff eventually failed, but it took a while (and the replacement lasted until the car was totaled).

Two weeks later?

Amazingly, it was on the order of quite a few months before failure. And supposedly that diff was questionable before the motor swap, so...

ProDarwin wrote:

Flight Service wrote: I was thinking Miata, but that doesn't seem to have a bunch of ratios (just the two 4.** and the automatic 3.9*)

There are many other ratios, but yeah, probably not 'cheap' as they won't be found in the junkyard. R160/R180/R200?

What is the tallest ratio you're looking for? The R160 in '02-~'05 WRX has a 3.54 ratio. I've been casually looking for a couple to adapt into my GT6 and Spitfire. They are a bit hard to find, to the point where I am almost hesitant to post this until I can get the ones I want.

rslifkin wrote:

jstein77 wrote:

rslifkin wrote:

z31maniac wrote: (the 4 cyl E30/E36 have the undesirable "small case" diff)

Which I saw a friend put 500whp through from a boosted S52 shoved in an E36 318 Diff eventually failed, but it took a while (and the replacement lasted until the car was totaled).

Two weeks later?

Amazingly, it was on the order of quite a few months before failure. And supposedly that diff was questionable before the motor swap, so...

Where as medium case diffs will go years with tons of track abuse and still not puke.

The Subaru/Nissan diffs have Looooooong snouts, it wouldn't surprise me if you didn't couple them directly to the tail-shaft of a MG Midgets transmission.

Old corvette and jag it's used a Dana 44. You won't find more gear options than that, and they aren't that heavy.

FYI, the E36 medium case diffs in limited slip seem to trade at around $400, even though they're relatively high mileage.

I can't remember their name, but there's an outfit on line that sells replacement friction discs so a DIY-er can refresh a tired one at home, and even increase the level of lock quite a bit, rather than paying $1,000 for a pro rebuild.

I have a track car near-done that will be putting about 250HP/320TQ (crank) to one, and I'm not worried about that in the least. Second draft of the motor will be more like 350HP/400TQ (crank) to one, and I'm a little less sure how long that will last. I know of several that have hung in there, but most of them were street rod/drift cars, not heavy redline track use.

In reply to JBasham:

Simple answer is to find a z3 Torsen equipped rear end if you never want to have to rebuild it.