Strongest rear end- MSM or FC? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 03-04-2011, 07:54 PM   #1
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Default Strongest rear end- MSM or FC?

So I'll be getting some 3.63's in the future, and while I'm at it I'd like to optimize my differential.

Would getting an FC rear diff cover make it stronger, or getting a MSM rear end with the bigger axles?

Eventually I plan on it being a 450whp HPDE car with an OSGilken... well down the road, so I'm wanting the most reliable way I can go.
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Old 03-04-2011, 08:07 PM   #2
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A Torsen will handle 400whp...not sure about 450whp. How much rwtq?
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Old 03-04-2011, 08:15 PM   #3
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Not sure, it'll be a while before I get to that power level. Probably 350-370wtq, if I estimate correctly.
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Old 03-04-2011, 08:43 PM   #4
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Ill let you know how mine holds up in the coming weeks
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Old 03-04-2011, 09:10 PM   #5
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I know it'll last up to street use, I'm not really worried about that, if I have the OSG... the torsen would be unhappy at that high of a HP at the very least. I'm more worried about breaking off ears or axles.
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Old 03-04-2011, 09:57 PM   #6
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In for interested.
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Old 04-01-2011, 02:25 AM   #7
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s5 fc rear end good for 400hp
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Old 04-01-2011, 02:44 AM   #8
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Quote:
Originally Posted by Reverant View Post
A Torsen will handle 400whp...not sure about 450whp. How much rwtq?


Quote:
Originally Posted by Savington
Blowing the 7" Torsen at Sacramento Raceway, April 26th 2008. Estimated power is approximately 230-235whp.
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Old 04-01-2011, 02:58 AM   #9
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Damn. Look at all the violence to that wheelhop. No wonder it broke.
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Old 04-01-2011, 04:10 AM   #10
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I've tuned several 230whp+ cars so far, no broken Torsens. What can I say?
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Old 04-01-2011, 08:41 AM   #11
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TorSens turn into open diffs. with too much torque (240+) and sticky tires. Even a FC clutch will do this and act liek a on/off switch. Get the OSG.

TorSens hold up pretty good...unless you wheel-hop them to death.
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Old 04-03-2011, 08:56 PM   #12
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Have you thought about switching to an 8 inch ring gear setup?
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Old 04-04-2011, 04:35 AM   #13
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Quote:
Originally Posted by Doppelgänger View Post
TorSens turn into open diffs. with too much torque (240+) and sticky tires.
How does that work? I'm not disagreeing, I just don't understand how it could happen? The TorSen is a torque biasing differential, the torque is biased through gearing. If there was 'slip' there's be no teeth left?
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Old 04-04-2011, 08:45 AM   #14
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Quote:
Originally Posted by richyvrlimited View Post
How does that work? I'm not disagreeing, I just don't understand how it could happen? The TorSen is a torque biasing differential, the torque is biased through gearing. If there was 'slip' there's be no teeth left?
They weren't designed to handle double the torque or massive differences in load from one wheel to the other. We also run them at 275*f on the track which is probably another stress they weren't designed for.
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Old 04-04-2011, 08:55 AM   #15
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So how does it 'become open' then? that's the bit I really don't understand.

If it was a clutch diff I could see the power overwhelming the plates, but with gears? it's either working or it's broken?
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Old 04-04-2011, 09:55 AM   #16
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Kinda like how TorSens will go into "open mode" when one wheel is off the ground or one wheel on ice/snow. It's called 'torque bias ratio' and it has to do with how much torque it can divide between both sides. If you load it up with a lot of torque in a situation where you're asking it to split up the difference (in a tight turn), it simply can't do it and sends all the torque to one side...the side with the lease resistance.

Quote:
The Torsen differential works just like a conventional differential but can lock up if a torque imbalance occurs, the maximum ratio of torque imbalance being defined by the Torque Bias Ratio (TBR).[3] When a Torsen has a 3:1 TBR, that means that one side of the differential can handle up to 75% while the other side would have to only handle 25% of applied torque. During acceleration under asymmetric traction conditions, so long as the higher traction side can handle the higher percentage of applied torque, no relative wheelspin will occur. When the traction difference exceeds the TBR, the slower output side of the differential receives the tractive torque of the faster wheel multiplied by the TBR; any extra torque remaining from applied torque contributes to the angular acceleration of the faster output side of the differential.
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Old 04-04-2011, 01:30 PM   #17
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I know they are unpopular in the miata world, but it would be nice to find a spool option that isn't "just weld it lulz".
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Old 04-04-2011, 02:12 PM   #18
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OsGiken with MSM axles? = S2000 OS G + msm axles.
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