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Old 07-19-2012, 02:39 PM   #21
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Originally Posted by sixshooter View Post
I believe the torque sensing diff is the most commonly used unit in track Miatas, but that might be due to abundance and relative low price rather than superiority. As I recall, the TorSen is more likely to allow one drive wheel to briefly spin faster than another but less likely to allow on-throttle oversteer. A tight clutch type LSD can be more prone to on-throttle oversteer, especially in the wet. A TorSen will allow some initial overspin of one wheel relative the other before locking in.
No. This description of a torsen is a fairly accurate description of a new viscous type, but is not an accurate description of a torsen (gear type).

All limited slips will, by their nature, spin the inside tire at the same speed as the outside tire, as soon as the torque delivered exceeds the grip capability of the inside wheel. This adds oversteer by diminishing the cornering grip given by the inside tire, and adds understeer by the extra moment generated by the unbalanced couple between the two rear tires driving forces. Before this point (when not spinning the inside tire up) the gear type is only adding a tiny fraction of the understeer moment, and none of the grip loss on the inside tire. The clutch type is still doing a little of both. This means the gear type should theoretically be faster if the suspension is setup around it and the lines are adjusted to compensate.

I have an RX7 clutch type in my Miata, and in practice, it works out decently well... better than I would have expected. The only place where it seems to give anything up to a gear type is in low speed sweepers where you need to late apex, but open the throttle early to get some spool in the turbo. Enough throttle opening to do anything for spool adds an intolerable amount of understeer. I expect this difference would be transparent through higher speed corners, but have very little firsthand experience.
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Old 07-19-2012, 03:11 PM   #22
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Originally Posted by karter74 View Post
I have also heard stories of people grenading torsens on bumpy tracks. Going at a high rate of speed , bump a curb or whatnot, puts one tire in the air while under WOT and when it comes back down, the shock on the drivetrain cause the diff to let go. Have no actual experience with this, just hearsay.
+1 on this, it's Keith at Flyin Miata that posted first-hand experience on Torsen vs. clutch type as installed in Trackdog and run on a track where the fast line necessitated running over curbs. Keith's conclusion was basically if you track the car and running over curbs is a regular part of the programme, you will need a clutch-type diff to avoid destruction of the diff.

With a one wheel impact a geared Torsen is going to be trying to do it's 3:1 (or whatever) torque multiplication dance, trying to transmit that shock load through to the wheel with traction, but... it will be multiplying that shock by it's spiderset gear/torque ratio and the energy will break parts when their limit is exceeded. In comparison a clutch pack diff will be absorbing that shock energy by converting it to heat from friction and slip in the clutch pack.

No curbing, dry track, and I would run a geared Torsen (I am, type II Fuji) because I need to invoke oversteer when I want it and this you can have with a Torsen. A clutch pack is going to be more forgiving for car control in the wet and in the snow, but wet+snow isnt' a situation where I will be racing.

I believe this bit of advice about using a clutch pack diff if you are going to be curbing it is about three years old you can always call Keith at FM to ask him what his latest opinion is, first-hand info is only a phone call away

Last edited by Fukalyal; 07-19-2012 at 03:39 PM.
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Old 07-19-2012, 03:16 PM   #23
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I really want to rebuild this RX7 diff, then sell both Torsens and buy a Giken. lol
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Old 07-19-2012, 04:35 PM   #24
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Originally Posted by Fukalyal View Post
A clutch pack is going to be more forgiving for car control in the wet and in the snow, but wet+snow isnt' a situation where I will be racing.
Have you driven both types in snowy conditions? The clutch type can easily have enough preload to act like a spool, where the transfer on a gear type is proportionate to the torque input, so with little total grip, it acts like an open diff.
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Old 07-19-2012, 05:27 PM   #25
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Originally Posted by Rocwandrer View Post
Have you driven both types in snowy conditions? The clutch type can easily have enough preload to act like a spool, where the transfer on a gear type is proportionate to the torque input, so with little total grip, it acts like an open diff.
I have, but my clutch pack experience was the factory Mazda LSD. Brand new, it was a strange animal in the snow, chattering drive power back and forth to both rear wheels when it slipped, strange enough I videotaped it in the snow and showed it to my dealer to see if something was wrong. It was driveable though.

My geared Torsen in the snow is hilarious on the opposite end of the scale. Most notably, if I came to a stop and prepped to turn Left (like preparing to enter a business off main street and waiting for traffic to pass) when I got on the gas the Torsen pushed the car straight ahead as if the wheels were not turned.

The Torsen repeated this "straight push" in the wet on fresh asphalt once. From a dead stop, wheels full lock to the left, ease in the clutch and brrprprprprpr the front tires just push and skid across the pavement and the car goes straight ahead. Tap the brake to put a little load transfer on the front, and that's all that would take to grip the front tires and 'break' the torsen loose and allow the car to turn.

Neither of these two "straight push" type things happen enough to matter, maybe three in 12 years of driving on it.

In snow I would rather have an open diff than either Torsen or LSD.

In the dry the Torsen makes for great low speed corner exit. Lots of grip and little drama.

Last edited by Fukalyal; 07-19-2012 at 05:38 PM.
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Old 07-20-2012, 01:58 AM   #26
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I have driven both and prefer the rx-7 unit. The torsen if you lift/unload the inside tire enough you loose drive off the corner, may not be an issue in a turbo car but in low power miata's it is a lap killer.

Last edited by hingstonwm; 07-20-2012 at 02:10 AM.
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Old 07-20-2012, 10:36 AM   #27
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Originally Posted by Fukalyal View Post
I have, but my clutch pack experience was the factory Mazda LSD. Brand new, it was a strange animal in the snow, chattering drive power back and forth to both rear wheels when it slipped, strange enough I videotaped it in the snow and showed it to my dealer to see if something was wrong. It was driveable though.

My geared Torsen in the snow is hilarious on the opposite end of the scale. Most notably, if I came to a stop and prepped to turn Left (like preparing to enter a business off main street and waiting for traffic to pass) when I got on the gas the Torsen pushed the car straight ahead as if the wheels were not turned.

The Torsen repeated this "straight push" in the wet on fresh asphalt once. From a dead stop, wheels full lock to the left, ease in the clutch and brrprprprprpr the front tires just push and skid across the pavement and the car goes straight ahead. Tap the brake to put a little load transfer on the front, and that's all that would take to grip the front tires and 'break' the torsen loose and allow the car to turn.

Neither of these two "straight push" type things happen enough to matter, maybe three in 12 years of driving on it.

In snow I would rather have an open diff than either Torsen or LSD.

In the dry the Torsen makes for great low speed corner exit. Lots of grip and little drama.
My open diff MR2 will do that when it is cold out (say sub 50F) with sticky tires. It does something similar in reverse backing to turn around in my driveway in the morning. Not saying the diff didn't cause it in your case, just contributing a data point.
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Old 07-20-2012, 09:01 PM   #28
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Originally Posted by hingstonwm View Post
I have driven both and prefer the rx-7 unit. The torsen if you lift/unload the inside tire enough you loose drive off the corner, may not be an issue in a turbo car but in low power miata's it is a lap killer.
My experience with the Rx7 unit was that it would do the same thing (inside rear tire spin with ~200wtq), but the decel lock-up wrecked the turn-in characteristics of the car too. The worst of both worlds.
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Old 07-20-2012, 09:18 PM   #29
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Originally Posted by Savington View Post
My experience with the Rx7 unit was that it would do the same thing (inside rear tire spin with ~200wtq), but the decel lock-up wrecked the turn-in characteristics of the car too. The worst of both worlds.
Have not noticed that with the Rx7 unit in my FP car, of course I only have
~112wtq. Have not noticed any issues at turn in...are you speaking of over/understeer? Im sure we are running different rubber, I am on Hoosier radial slicks, 215 45 15, 80 compound. Also, suspension set ups are different,
perhaps driver feel is different too.
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Old 07-21-2012, 04:00 AM   #30
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Originally Posted by hustler View Post
I really want to rebuild this RX7 diff, then sell both Torsens and buy a Giken. lol
I want to try a Giken out but no one around here has them, all torsen fanboys.

I've heard nothing but good things but idk if it beats my 100$ lsd lol
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Old 07-22-2012, 10:22 AM   #31
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I was at the Giants Despair Hillclimb last weekend, and the devil's elbow had enough simultaneous change in camber and elevation that my inside rear wheel would lift momentarily. The torsen stopped working and it'd just spin it all day long... very aggravating, but at least the fans liked it
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Old 07-22-2012, 10:01 PM   #32
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Originally Posted by Handy Man View Post
I was at the Giants Despair Hillclimb last weekend, and the devil's elbow had enough simultaneous change in camber and elevation that my inside rear wheel would lift momentarily. The torsen stopped working and it'd just spin it all day long... very aggravating, but at least the fans liked it
Proper ebrake application can fake the torsen into working correctly. Or if you want to rebuild it you can add more preload.
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Old 07-23-2012, 03:30 PM   #33
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Proper ebrake application can fake the torsen into working correctly. Or if you want to rebuild it you can add more preload.
preload a torsen?
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Old 07-23-2012, 06:02 PM   #34
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Originally Posted by Rocwandrer View Post
preload a torsen?
Yup, they all have a preload setup of some sort. Normally belleville washers. Its mostly to take up slack in the design to prevent noise. But it can be used to at least get a bit of torque to the wheel on the ground when one is in the air. Over do it though and the complete thing turns to ----.
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