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Old 01-15-2014, 05:17 PM   #1
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Default What diff is this and how strong is it?

I just bought this and the guy didn't know what he had.....problem is neither do I. It looks like an FC diff, are those stronger? What are they rated to? This was in a LS1 swapped Miata, what I am building.....
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Old 01-15-2014, 05:19 PM   #2
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Need more/better pics
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Old 01-15-2014, 05:25 PM   #3
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That is all I have.....I haven't picked it up yet. He said it was a "built" torsen diff from a miata..... He bought it used and doesn't know miatas so he is clueless.... I plan to pick it up next week. I bought the package for the other parts included but if this is worthy it will make things easy!
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Old 01-15-2014, 07:20 PM   #4
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Yes FC diff. Will only be stronger if its from a Turbo II, regular FCs have the same diff as Miata
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Old 01-15-2014, 07:32 PM   #5
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I like the longer pinion housing. Should be stronger and better ensure proper alignment under torque. But I don't know what the weak link is on a torsen.....He said it was 4.1 ratio, does that tell us anything? Not sure if the TII was 4.1 and other FC's were different?
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Old 01-15-2014, 08:39 PM   #6
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I thought TII diffs were clutch type, not Torsen.
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Old 01-16-2014, 12:15 PM   #7
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This is a turboII rear from an rx7 I have this same rear in my car and it is holding up strong. It is most likely a LSD clutch type will hold a decent amount of power before the clutches burn up. I picked up an torsen out of a newer RX7 for when my lsd finally takes a crap or you can still rebuild the clutch packs all parts are still available.

As far as installing it mounting in the car is easy.

1. Use miata diff mounts poly or delrin
2. to get the pinion angle right I used a set of shims for a leaf spring car worked perfect.
3. axles. You can use 1.8L axles. The easiest way to do this is find NB axles that are one piece so no more stub shafts. Replace the RX7 axle seals with NB miata axle seals.

I dont remember the exact configuration off the top of my head but I believe you can also use 1.8 miata two piece axles and stub shafts. but still need to replace the axle seals the difference is 1mm I believe they look like they will work but they will leak.
The hard part. you need to find a way to either adapt the PPF to the diff or get rid of your PFF all together.

In my case I have a freak swap in my car so I made a trans cross member and I also made a mounting system for the diff. I can say there are much easier ways to brace the diff other than what I did. I will see if I have some pics.
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Old 01-16-2014, 12:19 PM   #8
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I made a cross member under the car using some square tube mounted a plate to the side of the diff with the 3 mounting holes and then used a link to hold it in place. I would have been much better off taking out the rear crossmember and making a link to go from the plate on the diff to the top of the crossmemeber like most people to. Either way it works I have tested it with 90mph wheel spin and she is holding up strong
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Old 01-16-2014, 12:21 PM   #9
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it doesn't necessarily have to be a turboII rear. I could be from a 84-85 rx7 with the thrid member and will always leak from the axles because the diff doesn't have the recess for the circlips!

but i bet it's an 8" FC rear with a clutch diff.
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Old 01-16-2014, 02:02 PM   #10
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Thanks guys. PPF isn't an issue as this build is LS1/T56. The read subframe as pictured came out of a LS1 swapped Miata. I will likely go 8.8 Ford for the desired ratio, but it is good to know what I have.
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