Duke48

As in the subject what is better from driving standpoint and also what is more predictable? I am sick of one tire fire on slightly slippery surfaces.

Zirconocene

I forget where I saw this discussion recently, but this came up as a well-liked option (no affiliation): https://osgikenusa.com/collections/l...ducts/pr061-ha

Cheers

chudson

I did some research on this recently. I think the intended use alters the answer. Porsche switched from the clutch type ZF in the ‘92 968 to the gear type Torsen in ‘93. I think that a Torsen is plenty fine for street use, but I want to swap from the Torsen in my track car to a clutch type and hopefully, I can request a locking ratio. I think the choices are Quaif, Elite, Guards, OS Giken and Wavetrac. A well known supplier suggested the Elite based on his experience and also, I’m told that there are still some supply chain issues - another possible reason that he may have suggested Elite. That may also influence your decision if needing to purchase soon. I hope this helps and also hope we hear some other opinions.

Cliff

KevinGross

If your intention is serious track (DE or race) or autocross performance, a true LSD is the best option, and the Guard LSD is the best one out there. The Guard unit comes with two locking ratios selectable with its stock pressure rings: 40/60 and 50/80. You can swap in a set of Boxster pressure rings (ramps) if you want an 80/80 set-up -- but you don't want that. Almost every one I install in a 944-series goes in with the 40/60 option.

If you can find a factory LSD for your 944, it's a great option with its 40 / 40 lock. Try to avoid using a generation-1 version that has its ring gear mounting flange welded to the case. The welds fail and do a lot of damage. Porsche and ZF woke up to this, and switched to a one-piece casting a few years into the 944 lifetime. Both the Guard and factory LSDs can be serviced easily when the time comes, and the needed parts are readily available.

A TBD (torque-bias differential) is another option, and Wavetrac is the best one currently available, to my knowledge. Quaife used to make both LSDs and TBDs for 944-series but as far as I am aware they are no longer being made. The big difference with a TBD when compared with a LSD is its performance under decel (braking). Normally, a TBD goes full open under decel. Wavetrac has a trick to their design where is goes to full lock. Neither is, in my opinion, great for car handling for example when trail braking into a corner. But I have to say that I have a customer who keeps winning at SCCA Nationals and he loves his Wavetrac, has no issues with its decel behavior!

The OS Giken is popular on Internet discussion boards and is less expensive than most other options. My issue with it is that so many of their claims to technical advantage make no sense to me. Top of that list is its claimed "100% lock." You categorically do not want a LSD that has 100% lock: that's like driving with a welded differential, and the behavior is that if you lose traction on one side of the car, the driven wheel with traction will instantly pivot the car into the nearest vertical object. From servicing a few customer transmissions that showed up with an OSG, and from their promotional material, I can tell you that their multi-plate units have a lot of lock-up and a whole lot of break-away torque. Neither is desirable, this is not a case of "more is better." The 40% you get with the factory or Guard unit is a very good number for a 944-series car. Cheers,

chudson

Kevin - thanks for posting. I have 2 follow-up questions. 1) I'm guessing that all of these recommendations are the same for a dedicated 968 track car 6 speed? 2) You mentioned every brand except for Elite. Any opinion there? Thanks in advance

Cliff

walfreyydo

I have a Guard TBD in my S2 trans for the last year and its performed well and has been a great improvement over the stock non-LSD trans. I mainly use my car for autox and HPDE. I think the Guard TBD units are a good value and overall TBD's are priced lower than actual clutch-based LSD's, while getting 75% of the same benefits as a true LSD with none of the maintenance downsides (replacing clutch packs).

Personally, Ive seen a great increase in traction, especially coming out of turns and cornering under load since moving to a TBD and overall the car is just much more fun. You will really notice it when accelerating while cornering. I would say unless you are looking for a 100% dedicated race situation, a TBD works just fine for most casual autox/HPDE situations.

In addition to everything Kevin mentioned I have read that with TBD's when one wheel lifts off the ground you lose posi, although I have never experienced this myself, I could see that being an issue in a true race situation. I think regardless of whether you go TBD or LSD, either will dramatically benefit how the car behaves.

KevinGross

Hi Cliff, yes, no change for the 968's transmission or what suits the car. I have never heard of Elite and have not seen their technical doc or an example of their differential. Cheers,

michaelmount123

Great info from Kevin! His experience surely counts here.

Tom Pultz

Karl at Racer's Edge runs an Elite Racing LSD in his dedicated track car. Currently, I have an order with him for a G50 OS Giken LSD [although I might cancel that based on Kevin's response] for a 968 trans Kevin is putting together for me, but supply chain issues are pushing that out to the end of March or early April, so Karl suggested the Elite, which is made in the UK. From the only picture and info I could find it looks remarkably similar to the OSG. Hmmm.

Here's what Karl had to say about the Elite, "Brian at BMC&G (probably the best Porsche transmission guy in the country) buys Elite from me, Brian did all the Motorsports rebuilds for 20 or more years on the various racing circuits for Porsche, he was the guy at the Daytona 24 hours and other big races doing all the boxes. He likes them which says a lot (he just ordered a G50 Elite LSD the other day from me) and he has one in his personal 944 Turbo. Not a hard sell, just the facts."

FWIW, I have a Guard Transmission LSD in my 944 S2. I bought it years ago when we could buy direct from Paul Guard [note, it's Guard, NOT Guards]. I like it and it's not too noisy, just an occasional noise is slow speed corners.

Cost no object, I'd install another Guard unit, but who knows when they might be available. Supply chain issues are really a PITA.

Cheers.

The trans Kevin is doing for me came with an M220 Torsen, which has ~ 60K miles on it. Anyone reading this can have it for $1000.

Duke48

Ok, now I know I want to go with Torsen TBD, but I see one issue, I have external oil cooler in my trans(version for Switzerland). Do I need drive for the pump? I see sth regarding that here: https://www.guardtransmissionllc.com...differentials/

chudson

Thanks Tom - I don’t know when or where I got “Guards” but I read it once and it stuck.

PM sent

Cliff

SirLapsalot

Not disagreeing with Kevin's advice at all, and not a direct correlation with our 944/968 cars, but FWIW I ran OS in FWD IMSA ST cars for a number of years with good success. I liked that you could tune the locking behavior with their spring kits. It's been long enough now that I can't recall what we set static preload to but I don't remember having trouble setting it, or it ever being too high. I do recall replacing friction disks fairly often though. Anyway, I don't think the OS is a bad diff, and I think it can be setup to work well.

KevinGross

Guard can provide the oil pump drive gear you will need with one of their LSDs. However, if you want a TBD, my understanding is that Guard no longer offers them -- I'm going to check with Matt to confirm, perhaps I am wrong. (I just serviced one for another customer.) If I recall correctly, the Wavetrac TBD works with Porsche's oil pump drive gear from an open differential, rather than the Porsche LSD version of the gear. So you would want 016.115.165.A (open differential version) and not 016.115.165 (LSD version). Neither version is available from Porsche. I have a few of the open differential version on the shelf, if you get stuck finding one closer to home.

Update: Guard confirmed to me this morning that they are not making TBDs for the foreseeable future. Just LSDs.

Tom Pultz

I found this YouTube video about the operation of the OS Giken LSD:

tims944

i currently have a custom built 5Y box with guard diff, not sure if torsen or lsd though. it had a cooler fitted to it aswell.
it is technically for sale as a complete box but could potentially pull the diff and offer it, i thought it was a modified 5R until i removed it.