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Old 07-05-2012, 10:15 AM   #1
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Default Torsen vs. RX7 LSD

I've had a Torsen in the car since I originally built it back 3 years ago. The car was primarily used for auto-x and street driving. I've now turned the car to primarily being a track car and have read that the clutch-type RX7 GXL LSD is superior in tracking situations. But that's all I can find. No one says why, or if it will be lightyears faster.

I have access to said diff and a 1.8 open to make a usable diff if I trade my Torsen. I may ask for cash on top, but I'm unsure of the value of a RX7 LSD. My car will be down for a few months yet anyway and was wondering if its worth it to make the trade.

If I go this route is there anything you all recommend to replace/rebuild while I have it apart to swap carrier assemblies? Are there better clutch pack available and such?

Obligatory picture of car in its current state to show you I mean business.

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Old 07-05-2012, 10:31 AM   #2
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Not sure on the rx7, but I like the feel of the torsen, its amazing in basically any situation where you dont have an inside rear wheel off the ground. Its predictable, natural feeling, all around good. To me there are 3 performance characteristics of a diff that are important, power handling capability (ie wont break with the power you're making), feel, and being able to apply power in all situations. The torsen hits the first tow points amazingly and only fails on the 3rd one when lifting a wheel. And on that scale the only thing I see as an upgrade is the geiken. Since its predictable if setup correctly, feels good different from the torsen though, and if setup up right will put power down if you lift the inside rear. The rx7? It should hold the power and it should not spin up the inside rear if you lift it, but how does it feel?
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Old 07-05-2012, 10:52 AM   #3
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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.
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Old 07-05-2012, 12:36 PM   #4
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Originally Posted by Sokool View Post
...but I'm unsure of the value of a RX7 LSD.
I paid $100 for an open 3.909 just because I wanted the R&P gears. The LSDs don't go for a whole lot more because most people assume if you're buying a used one that it will need to be rebuilt, and the discs & shims cost a little dough. On rx7club, complete 3rds out of the carrier go in the $150 ballpark IIRC. Don't hold me to that though; it's been a couple years since I looked. I would assume you could get more if you had dated receipts to prove it was serviced recently.

A clutch type diff will be better than a Torsen at the drag strip but for a road car I'm keeping the Torsen until such time as I ever have the need for a Giken.
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Old 07-05-2012, 01:06 PM   #5
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A tight clutch type LSD can be more prone to on-throttle oversteer, especially in the wet.

^^^ this. if I was building a drift car, id put the rx7 clutch diff back in.
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Old 07-05-2012, 01:08 PM   #6
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Drag Racing = clutch diff
Track/Auto Cross = Torsen diff
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Old 07-05-2012, 01:31 PM   #7
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Everyone seems to be steering towards keeping the Torsen. Just because clutch-type is more prone to oversteer doesn't necessarily mean it's not faster on the track. Looking to see who has possibly used both and their thoughts on both.

Like sixshooter said, is the reason everyone uses Torsen because of availability and price or are they faster then any other available option?
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Old 07-05-2012, 01:40 PM   #8
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Either diff will be fast at the track. The issue is, what one do you like the feel of, and does one induce effects that are detrimental. The torsen spinning the inside wheel if it lifts only makes you a hair slower coming out of the corner. The clutch pack locking up and spinning both wheels can make you a lot slower. But the big thing is feel. If the clutch pack was 1 second a lap faster but felt like garbage I wouldnt run it because I know that with me driving it I'd be slower due to lower confidence. Just because the car is faster from an engineering perspective doesnt mean that its possible to drive it that fast. See Lotus 79.
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Old 07-05-2012, 01:45 PM   #9
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confidence is important; had none with rx7 rear.

to be fair, it had preload to the point of it being a welded diff...
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Old 07-05-2012, 02:47 PM   #10
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I have both in different cars. Both have their merits but my preference is the RX-7 diff. I did not adjust the preload of the diff when I installed it (found ALL the plates to be within brand new spec) and enjoy the smoothness of it.

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.

Last edited by karter74; 07-05-2012 at 04:09 PM.
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Old 07-05-2012, 02:54 PM   #11
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you can easily destroy a torsen with clutch dumps.
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Old 07-05-2012, 08:33 PM   #12
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I've never used the RX7

In theory a TorSen is better at distributing torque to the wheel with more grip than a clutch type (probably why people feel it doesn't break the rear end free as easily) however, it also saps a relatively large amount of power, and in doing so creates a lot of heat.

Of course, just because it theoretically transfers torque better, doesn't mean its actually faster or better. Sav has reported dropping significant time by switching from a TorSen to an OS Giken, so obviously a well setup clutch type can be superior depending on your driving style and situation.

Also, if you're driving the wheels off the thing and bouncing off curbs all day, the lack of power with a wheel in the air might be an issue.

Last edited by Handy Man; 07-06-2012 at 09:25 AM.
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Old 07-06-2012, 12:45 AM   #13
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Quote:
Originally Posted by Sokool View Post
Everyone seems to be steering towards keeping the Torsen. Just because clutch-type is more prone to oversteer doesn't necessarily mean it's not faster on the track. Looking to see who has possibly used both and their thoughts on both.

Like sixshooter said, is the reason everyone uses Torsen because of availability and price or are they faster then any other available option?
I have used both. The Rx7 LSDs are total garbage. You can preload them, but the turn-in gets worse and worse, and they will never adequately lock in low-grip situations. You end up with all of the downsides of a 2-way diff and none of the upsides.

I ran mine for a year and traded it for a Torsen. They are awful differentials and they have no place anywhere but a dragstrip.
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Old 07-06-2012, 02:27 PM   #14
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Seach fatherleadfoot on miata.net. He was contantly fiddling with shims and preload, and IIRC left with the same opinion as Andrew (Savington).
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Old 07-06-2012, 03:21 PM   #15
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Glad I asked. Thank you guys for all your input. Torsen it shall stay!
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Old 07-08-2012, 02:31 PM   #16
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you can easily destroy a torsen with clutch dumps.
i have clutch kicked the ---- out of my torsen with no issues drifting. They are alot stronger than i would have thought. it has never given me any issue.
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Old 07-08-2012, 02:41 PM   #17
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Quote:
Originally Posted by Savington View Post
I have used both. The Rx7 LSDs are total garbage. You can preload them, but the turn-in gets worse and worse, and they will never adequately lock in low-grip situations. You end up with all of the downsides of a 2-way diff and none of the upsides.

I ran mine for a year and traded it for a Torsen. They are awful differentials and they have no place anywhere but a dragstrip.
What about in a 150whp daily/future racecar?
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Old 07-08-2012, 06:56 PM   #18
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i have clutch kicked the ---- out of my torsen with no issues drifting. They are alot stronger than i would have thought. it has never given me any issue.
Do it when trying to MAINTAIN traction...

Ie. On a drag strip. Not clutch kicking around a corner. Big difference in the load the hexigears see and how manly you are.

Last edited by Braineack; 07-09-2012 at 10:00 AM.
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Old 07-08-2012, 10:52 PM   #19
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Old 07-19-2012, 06:59 AM   #20
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Quote:
Originally Posted by Savington View Post
I have used both. The Rx7 LSDs are total garbage. You can preload them, but the turn-in gets worse and worse, and they will never adequately lock in low-grip situations. You end up with all of the downsides of a 2-way diff and none of the upsides.

I ran mine for a year and traded it for a Torsen. They are awful differentials and they have no place anywhere but a dragstrip.
The problem with the rx7 lsd's is they are only as good as they are rebuilt and set.

I have no complaints with mine (only took 3 rebuilds to get it to the way I liked it though). After a few months of driving with a torsen in my s2000 I can't wait to get rid of it, miatas rearend feels much more predictable.
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