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M3 Track: Racing and DE Best mod for speed is learning to get the most out of what you currently have. Tracks and DE's is the place to start!


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Old Mon, Sep-25-2017, 03:38:15 PM   #1
Move_Over
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Default Torsen/Helical vs. Clutch type LSD

Good morning gents. As a few of you know I am about to redo my rear end and am wavering between a Torsen/Helical LSD (mFactory or Wavetrac), or a ZF type 2 way 2 clutch diff with a 40% lockup.

I think I have read just about every page on the internet discussing the differences but wanted to get you all's expert opinion before i pull the trigger on anything. Enter Feffman, Thundermoose, BIGJAE!

First of all, my car is an 80% track car. It sees street time every once in a while. I would consider myself an intermediate driver. Typically run INT/ADV with most groups, been tracking for about 3 years now.

From all of my research, it looks like the helical/torsen diff is an easier and more predictable LSD to drive around the track. Doesn't push the car, no added understeer, and really looks for the most grip constantly. HOWEVER, the one main gripe about this type is that if you lift a wheel, the power goes to that wheel until contact comes back. Now, i do my best not to curb hop, but sometimes it is necessary. I'm not 100% sure if a wheel is lifting, but i'm sure it has happened.

The installer here swears by the helical type, I was prepared to buy a clutch type, but he told me to research the Wavetracs and MFactory over the weekend. He said he has a ton of success and is faster with them due to them being less intrusive. He sells neither, so it's an unbiased opinion.

On the flip side, i hear for RWD cars that a clutch type is better, but can cause some push, and the abrupt lockup can be intrusive around tight tracks.

Pricing is around the same. Found a supplier for a rebuilt ZF type for around $1000 shipped, the Mfactory I believe i can get for around 900 (they have a 30 day return policy if you do not like them which is pretty cool). And the wavetrac will be around 1295.

Let me know your thoughts. Thanks!
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Old Mon, Sep-25-2017, 04:15:16 PM   #2
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Default Re: Torsen/Helical vs. Clutch type LSD

My thoughts are by no means gospel, but I went through the same decision process, ultimately ending up with a Drexler (http://www.autotechdriveline.com/diff_drexler.htm) clutch-type differential for a variety of reasons. Not the least of which is the wheel-lift issue which the clutched diffs address handsomely.

Here's a thought. If you go with the rebuilt ZF differential, and decide later on to change the ramp angles for more aggressive on-track prowess, you can pull the diff, strip it down and send the pressure rings to Dan at DiffsOnLine.com to have more aggressive ramp angles added. You can also have it modified to accept more clutches if needed as well.

Hope this helps.

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Old Mon, Sep-25-2017, 04:41:30 PM   #3
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Default Re: Torsen/Helical vs. Clutch type LSD

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Originally Posted by Feffman View Post
My thoughts are by no means gospel, but I went through the same decision process, ultimately ending up with a Drexler (http://www.autotechdriveline.com/diff_drexler.htm) clutch-type differential for a variety of reasons. Not the least of which is the wheel-lift issue which the clutched diffs address handsomely.

Here's a thought. If you go with the rebuilt ZF differential, and decide later on to change the ramp angles for more aggressive on-track prowess, you can pull the diff, strip it down and send the pressure rings to Dan at DiffsOnLine.com to have more aggressive ramp angles added. You can also have it modified to accept more clutches if needed as well.

Hope this helps.

Feff
Hey feff - looking forward to daytona in a few months. I'll be sure to come by and spend some time with you.

What other reasoning did you go with the clutch type? The ZF type i am looking at comes with 30/30 ramp angles. Not really sure what that means to be honest, which is another reason why i am considering the helical. Set it and forget it.

I like to adjust equipment, but i don't want it to take away from the fun of tracking. I'm not winning races, yet. lol
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Old Mon, Sep-25-2017, 07:06:02 PM   #4
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Default Re: Torsen/Helical vs. Clutch type LSD

I'm not sure why lifting a rear wheel is a concern for our cars. I've never seen a RWD car do that. Even if you go over a curb you should catch air only for a split second. I've driven a new M-lock and a 3 clutch diff (188mm in my 330). While the new M lock in my E90 M3 was pretty good, the 3 clutch diff in my 330 was better.

The best way to describe it is using a dance partner. The M lock is going to step on your toes from time to time whereas the clutch diff (when setup well) will do a really good dance with your right foot. Yes, the car will understeer more AND the rear end will react to your throttle inputs more with the clutch vs the M lock. If you lift mid corner, you will likely spin. Stick with the M lock if you don't want that. But if you like steering the car with your right foot...you want the clutch diff.

If you are not committed to the idea that your job is to manage weight transfer to generate grip then don't get the clutch diff. You're gonna understeer like a pig if you still brake, turn, gas in 3 steps.

Either way, you do want to get this right the first time. It's not cheap changing your mind and non-ZF clutch type diffs don't sell very well on the used market.



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Old Mon, Sep-25-2017, 07:14:25 PM   #5
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Default Re: Torsen/Helical vs. Clutch type LSD

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Originally Posted by Move_Over View Post
The ZF type i am looking at comes with 30/30 ramp angles. Not really sure what that means to be honest, which is another reason why i am considering the helical. Set it and forget it.



I like to adjust equipment, but i don't want it to take away from the fun of tracking. I'm not winning races, yet. lol

The way I understand it is the ramp angles determine how much the clutch pack will lock up. A 30/90 is a one way type and will lock on power only. A 30/30 will lock on power and decel.

Generally a higher number is a steeper angle which will provide less lock. So a 30/30 will provide more lock on decel than a 30/45. 45/45 will provide more lock on accel.

I think a 30/60 ramp angle is a common setup on BMWs that see track time.


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Old Mon, Sep-25-2017, 08:11:01 PM   #6
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Default Re: Torsen/Helical vs. Clutch type LSD

You don't have to entirely lift a wheel for the diff to transfer power to the unweighted one-- my stock clutch diff began acting like an open diff (one wheel fire) when I would unweight the inside wheel. This was pretty fun to have the car immediately oversteer exiting corners at autox, or hairpins on track, but it wasn't fast. I bought a rebuilt diff with 3 clutch 40% lockup and it's been great with no issues since.

I have no experience with the helicals. The fastest guys I know, with Solo, TT, and GTS championships to their names, run either Diffsonline clutch units or OSGiken based clutch units. E36/46s.
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Old Mon, Sep-25-2017, 08:36:21 PM   #7
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Default Re: Torsen/Helical vs. Clutch type LSD

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Originally Posted by Bimmerman325i View Post
You don't have to entirely lift a wheel for the diff to transfer power to the unweighted one-- my stock clutch diff began acting like an open diff (one wheel fire) when I would unweight the inside wheel. This was pretty fun to have the car immediately oversteer exiting corners at autox, or hairpins on track, but it wasn't fast. I bought a rebuilt diff with 3 clutch 40% lockup and it's been great with no issues since.

I have no experience with the helicals. The fastest guys I know, with Solo, TT, and GTS championships to their names, run either Diffsonline clutch units or OSGiken based clutch units. E36/46s.
Did that OEM 3 clutch have stock ramps? 1, 1.5 or 2 way? And, did you find yourself having to change your driving style with it? I'm a bit nervous as i haven't tracked a car with clutch style diff, and don't want to be in over my head and have to relearn the car that I am currently OH so comfortable driving.
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Old Mon, Sep-25-2017, 08:40:39 PM   #8
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Default Re: Torsen/Helical vs. Clutch type LSD

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Originally Posted by Move_Over View Post
Did that OEM 3 clutch have stock ramps? 1, 1.5 or 2 way? And, did you find yourself having to change your driving style with it? I'm a bit nervous as i haven't tracked a car with clutch style diff, and don't want to be in over my head and have to relearn the car that I am currently OH so comfortable driving.
Original diff was a 3.15 ratio bone stock diff, I think the 2-clutch 45/45 ramps or whatever it is the factory does. The new diff is a 40% lockup unit with the same ramps as stock, allegedly a 3-clutch unit. I don't know whether that constitutes 1/1.5/2 way or not.

I haven't had to change anything about my driving style. It feels like a stock diff that just will now put power down on corner exit. It might understeer a smidge more, but nothing super noticeable. The bigger difference was the 3.91 ratio makes the S54 sooooooooo much more fun.
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Old Mon, Sep-25-2017, 08:44:35 PM   #9
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Default Re: Torsen/Helical vs. Clutch type LSD

Quote:
Originally Posted by Bimmerman325i View Post
Original diff was a 3.15 ratio bone stock diff, I think the 2-clutch 45/45 ramps or whatever it is the factory does. The new diff is a 40% lockup unit with the same ramps as stock, allegedly a 3-clutch unit. I don't know whether that constitutes 1/1.5/2 way or not.

I haven't had to change anything about my driving style. It feels like a stock diff that just will now put power down on corner exit. It might understeer a smidge more, but nothing super noticeable. The bigger difference was the 3.91 ratio makes the S54 sooooooooo much more fun.
I just ordered a set of 3.91's this morning, excited about that with my 8200 redline.

Can you point me in the direction of where to find that similar diff that you ordered? And what type of pricing did you get on that? PM me if need be.
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Old Mon, Sep-25-2017, 08:49:44 PM   #10
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Default Re: Torsen/Helical vs. Clutch type LSD

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Originally Posted by Move_Over View Post
I just ordered a set of 3.91's this morning, excited about that with my 8200 redline.

Can you point me in the direction of where to find that similar diff that you ordered? And what type of pricing did you get on that? PM me if need be.
Would if I could!

I bought it used from an m3fourm member who had his local shop change out the ring and pinion and replace the clutches. I don't have as many details on the diff as I'd like, but it works really well so I haven't been too bothered by the diff's unknowns.
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