I was thinking that a Kaaz lsd would be the best choice for my 88 base model fc, but I recently heard that the differential from 89+ fc would work just as well and would be alot cheaper. Is this true?

 

it really depends on your application and usage. for reference though, the 86-88 LSDs that came from the factory were clutch-type LSDs, and the 89-91 LSDs were viscous-type.
from a performance perspective the clutch-type is superior, but they do evetually wear out/break. the viscous differentials tend to last longer, but the lock up characterisitics are very tame compared to the other diff types, and they do wear out too, you just probably won't notice.

i think the KAAZ diff is a 1.5-way clutch-type diff. usually these have fairly agressive lock-up. they are pretty durable also. these make them good for competition use. but, i don't think they are necessary for just street use.

IMO, best for street use:
- good condition/rebuilt S4 LSD
- swap in a Torsen diff from a 94+ Miata

for motorsports diff selection is a whole topic in itself.

if you want some more info on differentials, read here (or just google it): http://en.wikipedia.org/wiki/Limited_slip_differential

 

would u happen to know how much it would be to rebuild my diff then? My car is goin to see a fair amount of track days this coming season.

 

If it's a base model then there won't be an LSD in the rear end, it'll be an open diff.

 

hmmm lsd.

 

Id get an s4, and have a shop rebuild it with the thick plated mazdaspeed rebuild kit. the kaaz will cost you an arm and leg, but, for a begining racer, would be better, as most cant handle the decel lockup. I personally love it, but its a personal thing. If you like the feel of your car right now, then id say go with the viscous, as it will feel roughly the same, but if you want to be ubber in touch with the cars rotation in both acel and decel, then 2 way. If you just want to say you blew 2k on a kaaz diff so your sig came be bigger, then go with that.

 

some would argue that the Torsen type diff is the best out there in terms of lock-up characteristics and "feel".

 

The kaaz diff is only 8-9 hundred bucks.

 

Go with the Mazda LSD (clutch Type). I have a KAZZ and from my experience it is too harsh for a street application, low speed clunking, and unless you are making 400+rwhp it's not needed.

 

So are u sayin I should take one out of another NA?

 

If I were you I'd get a Torsen out of a Miata, unless you're planning on making a lot of power (250+).

 

agreed on the Torsen, EXCEPT it's more work because you have to swap in the differential from the Miata into the casing from the FC. this includes setting the backlash correctly.
plus i've been trying to find a Miata torsen and it's not that easy. rebuilt/new ones cost quite a bit also.

 

I have a Stock Torsen out of my 3rdgen FD..... if you want it. Name a price, I don't know what it's worth. It has about 30k on it.

 

the FD Torsen is good for NA, but more suited for T2 Apps. I bought a FD Torsen to be swapped in my S4 T2 Diff, since mine needs a rebuild, and i definately aint in the mood to spend 400bucks on rebuilding the sucker. I got the FD one for about 200 half the price and better characteristics for AutoX

 

So you have the clutch pack LSD out of a 86-89T2? How much do you want for it?

 

If he really wants LSD action he'd need to rebuild the S4 LSD anyway, as it's likely worn out by now. So that'll mean taking it all apart anyway, so a Miata Torsen won't be that much more work.

The TII and FD diff internals are swappable, but the TII and NA diffs aren't, the TII has an 8" gear, the NA has a 7", so they're not compatible.

 

Good info!

 

How much does it usually cost to get and S4 NA LSD rebuilt?

 

Probably about $300-$400 in parts, plus labour to rebuild it. If you're a member of Mazdaspeed then you should be able to get parts at a discount.

 

i havent swapped the Diffs from my car yet... i'll let you know when i do tho... it could be while, just to forewarn ya

 

**** just remembered, your right. The FD and TII are swappable. The Miata and NA are swappable. But they cannot swap each other (turbo and non-turbo). Good Call!

 

Yes, it only costs 8-9 hun, but itll cost another 5-6 hundred to put it in (by a shop).

 

yup, NA diffs are not interchangeable with TII/FD diffs. that's why i mentioned your only options, other than an aftermarket diff, are:

- good condition/rebuilt S4 LSD (NA)
- swap in a Torsen diff from a 94+ Miata

 

Alright thanx. I have alot of thinking to do now lol.

Ya I knew I could only get one from an NA. Mazdatrix has a chart of all rx7 interchangeable diffs on their site.