Miata Torsen swap - is it all that?: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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May 16, 2010 11:32 a.m. motomoron Reader

My 90' Miata is on stands and apart for bracing, suspension, and full urethane bushings. And an FM exhaust and cat and SS brake lines. And the car came w/ a new Exedy clutch, so maybe I should do it while I'm there...

Anyway, I've got a line on a full Torsen swap out of a '95. 4.3 axle ratio, includes drive shaft (c'mon everybody...) half shafts, diff+carrier, and hubs (!) for around 8 bills.

Obviously, it'll never be easier than now, and I can afford it. My $3000 Miata is rapidly turning into a $7000 Miata, albeit a perfectly sorted one.

I already have the M3 track car and Sprite play car - the Miata will be street driven and autocrossed in a "fun series".

Do I go for the Torsen? I'm thinking yes...
May 16, 2010 11:34 a.m. psteav Reader

'95 should have a 4.10 axle ratio unless the R&P has been swapped.
May 16, 2010 12:02 p.m. motomoron Reader

My bad...I meant 4.10. My car has 4.3. I reckon the 4.1 will be nice on the highway and while I haven't autocrossed it yet, a little more room at the top of 2nd gear is nice on bigger courses.
May 16, 2010 12:11 p.m. psteav Reader

Right on. I've had the swap lying in my garage for a while now, waiting to go under my '92. From what I've been told, the lack of buzziness is nicer on the highway, but it is definitely a noticeable downgrade in terms of acceleration. I'm planning on forced induction, so it didn't bother me as much. I don't autocross, but I could definitely see how you could be quicker on some courses by not having to shift to 3rd.

As far as durability goes, the later rear end is a LOT stouter than the early ones. IIRC the early cars had a 6" ring gear, which has been known to puke under moderately spirited use behind a stock 1.6. The 1.8 diff is a 7" ring gear and holds up to some pretty serious turbo motors. I don't think you'd be able to break it behind a N/A 1.6 unless you were trying to. If you have any thoughts about going forced induction later, you should definitely do the swap now.
May 16, 2010 12:42 p.m. amg_rx7 Reader

800 is a bit much for a 4.1 ratio torsen. Around me, I see them on craigslist for ~3-600. I see the 4.3 Torsens complete w/ driveshaft and axles for $800-1,000.
May 16, 2010 2:52 p.m. TJ Dork

motomoron wrote:

drive shaft (c'mon everybody...)

You all everybody? Is this a Lost reference?
May 16, 2010 3:35 p.m. Keith SuperDork

psteav wrote:

As far as durability goes, the later rear end is a LOT stouter than the early ones. IIRC the early cars had a 6" ring gear, which has been known to puke under moderately spirited use behind a stock 1.6. The 1.8 diff is a 7" ring gear and holds up to some pretty serious turbo motors. I don't think you'd be able to break it behind a N/A 1.6 unless you were trying to. If you have any thoughts about going forced induction later, you should definitely do the swap now.

Zactly. The 6" ring gear is a liability. The advantage of the 7" isn't just strength, but also different available ratios. I personally like the 4.10 with a 1.8. If that's the case up here, then I guess I'd like the 4.10 with a 1.6 at sea level
May 16, 2010 4:59 p.m. White_and_Nerdy Reader

If you're ever going to dramatically increase the horsepower (forced induction), you're going to want the Torsen over the viscous LSD that the 1.6 models came with. Basically, what Keith said, plus a VLSD won't handle that kind of power - a Torsen will.

Your acceleration will be slightly reduced with the higher final drive. A 1.8 with a 4.10 accelerates about as well as a 1.6 with a 4.30. The power and torque advantage of the 1.8 doesn't offset the higher gearing. Match that with a 1.6, and your car won't accelerate as quickly. If it was me, I'd hold out for a 4.30 Torsen from a 99+ car.

But that's just me. If you'd rather keep highway revs down, want the extra top end of 2nd gear, and accelerating more slowly doesn't bother you, then go for it. It'll definitely work and be fun, and that's what it's all about.
May 16, 2010 5:25 p.m. grimmelshanks Reader

should you go torsen? is a frogs arse water-tight?
May 16, 2010 8:54 p.m. motomoron Reader
- - I'm at sea level.
- - The price includes the 4.10 diff and the big cast aluminum carrier-member thing, the drive shaft (and I got my Lost reference wrong - forgive me, Charlie...) the 1/2 shafts and the complete hub assemblies.
- - Not right now, but eventually I suspect theres a supercharged 1.8 in my future.
- - The M3 is actually kind of fast, and the Sprite ~feels~ fast. And they both sound fast. The Mee-Otter doesn't need to be a rocket.
I'm gonna pull the trigger and do it while it's up.

Thanks for the info and goading...