[dave968]

I wanted to ask if anyone has had the opportunity to compare both types of LSDs in their own car, same driver and tracks, and does the theoretical advantage of the the ZF clutch-type LSD with lockup on deceleration and braking translate into into improved lap times on the track?

And what years did Porsche use the Torsen LSD in which cars, ?ever in race cars?

What type of LSD did the 944Turbo Cup and 944S2 and Firehawk cars have?

txs

-Dave

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[flash]

these would be really good questions for pete at rsbarn - he is really the resource for what was raced and when

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[cooz]

[quote name='dave968' post='42701' date='Oct 21 2007, 10:14 AM']I wanted to ask if anyone has had the opportunity to compare both types of LSDs in their own car, same driver and tracks, and does the theoretical advantage of the the ZF clutch-type LSD with lockup on deceleration and braking translate into into improved lap times on the track?

And what years did Porsche use the Torsen LSD in which cars, ?ever in race cars?

What type of LSD did the 944Turbo Cup and 944S2 and Firehawk cars have?

txs

-Dave[/quote]







i believe all 944 LSD's were clutch type only.....also think only early first year 968 optional LSD's were clutch type and Torsen type by 1993..



c'mon pete...do i have it correct?



norm mandell <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />

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[Charles Geer]

I used to run the Torsen Limited slip until we noticed that the inside rear wheel would spin freely during tight turns. We recently installed a used cup car diff (believe it or not it fits right in) with 75 % lock. Boy...you can now go flat out in fast turns that you would normally lift, and you can exit the tighter turns with both rear wheels under power. I now fly out of tuns that I used to get bogged down in.



Used cup diffs are readily availaable. I paid $1700 installed by J3 racing here in Atlanta. J3 are regulars with the American Lemans and Grand Am series.



Our next project is to make a true racing diff for the 968. This diff would shorten all of the gears considerably allowing you to be at full revs in 6th gear on the straights of most tracks.



My car is currently doing 135 mph on the back straight of road atlanta in 5th gear turning 6100 rpms.

The new diff will max out at 143 mph (instead of 160) in 6th gear turning 7000 RPMs in the process.



We chose 143 because we think that is the fastest possible speed a normally apirated light weight 968 will go on most tracks.

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[Eric_K]

I can't think of many scenarios where a Torsen would have an advantage over the cluch type on the race track. But, they are both way better than an open diff. I have been running a Quaife (torsen style), because that was what the car had when I bought it. I threw in a different box, which has an open diff, for a 4 hour race last weekend. There is a significant difference in your ability to put the power down, especially in the rain and tight corners. As long as you keep both wheels firmly on the ground, both styles should be similar when accelerating, but a torsen won't help you when braking. My next diff will be a clutch style.



Here is a good article on limited slips:

http://www.guardtransmission.com/velocity.htm



Charles -I think shorter 3-6 gears (like powerhaus II sold) would be better than a shorter R&P. Sure you could make better use of 6th with a shorter R&P but it would also make 2nd fairly worthless. I would prefer to keep 2nd where it is and pack the next 4 gears closer together.

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[flash]

having gone the route of shorter ring and pinions on other cars, i can attest to the fragility they can exhibit under hard load - if i was kind to 1st and 2nd, it was great, but if i dumped the clutch or applied too much to it, i snapped the ring gear



the 1st ratio is pretty good where it is - can't imagine a lower gear being useful - 2nd isn't bad either, and if it were any lower i think i would run out of room and be shifting to 3rd too often - while i would have liked a lower 2nd at P.I.R for turn 12, i think the bigger problem was that i was not driving well enough, and it really had nothing to do with the gearbox (loose nut behind the wheel)



i concur that it would be nice if 3-6 could be stuffed down though, and plan to do that the next time i have to get in there

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[Eric_K]

while i would have liked a lower 2nd at P.I.R for turn 12

C'mon Flash, a lower 2nd? Pick up the pace, T12 is a 3rd gear corner. <img src="/forum/images/smilies/968/biggrin.gif" class="smilie" alt="" /> Or at least it was. PIR is being repaved and several corners reconfigured.

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[dave968]

[quote name='Charles Geer' post='42726' date='Oct 21 2007, 10:50 PM']I used to run the Torsen Limited slip until we noticed that the inside rear wheel would spin freely during tight turns. We recently installed a used cup car diff (believe it or not it fits right in) with 75 % lock. Boy...you can now go flat out in fast turns that you would normally lift, and you can exit the tighter turns with both rear wheels under power. I now fly out of tuns that I used to get bogged down in.[/quote]



Do you mean 75% lock on deceleration?

What is the lockup ratio on the stock and Motorsports LSD, listed as acceleration/deceleration?

GT transmission lists 45/65 and 50/80, and when I talked with Paul Girard he recommended 50/80 for the 968.

What do you think?

Dave

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[flash]

lol - yeah - i was definitely feeling like i was dragging - rusty as an old gate - felt like i was really scrambling every other turn - couldn't find my rhythm - just as i was starting to loosen up a bit, i blew the clutch on the big straight



not sure how the heck i could be in 3rd there though - it's a pretty tight 180 combination turn from 11 that then dumps onto the straight with a slight bend that should be called turn 13 - i can't imagine going fast enough into there to be in third, and not sure i'd want to shift in the middle - would be nice though to be able to hit third going into "13"

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[sguy]

Flash, just for your future reference at PIR, if you take T10 up on the inside banking (you can get most of the car up there) then 11 is an easy shot over to 12, with some hard braking before 12. It is a bit intimidating to take 10 that high on the bank, and I had to work up to it, but it pays big. Look at some of Erik's video at PIR and you'll see the line. Cheers,

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[Scott Collins]

My 968 has an open diff and only runs on the street, through all 4 seasons.



What about snow? I lose all kinds of traction in the snow. One tire spinning and I am

going nowhere fast. Aside from the tires, what kind

of diff should a car have for the best performance in snow? I have to believe one is

going to better than another.



Thanks for chiming in.



-Scott

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[Charles Geer]

[quote name='dave968' post='42796' date='Oct 23 2007, 03:58 AM']Do you mean 75% lock on deceleration?

What is the lockup ratio on the stock and Motorsports LSD, listed as acceleration/deceleration?

GT transmission lists 45/65 and 50/80, and when I talked with Paul Girard he recommended 50/80 for the 968.

What do you think?

Dave[/quote]



I think the lock is on acceleration. If I remeber correctly my diff acts as a open diff on deceleration and entering turns (wheels spin freely) and then it locks the wheels to power out of corners. They handed me back my Torsen diff internals in case anybody wants to purchase.



They had to do some "shimming" (I have no idea what that means...) but for the most part it was a direct exchange of internal parts. From the outside...everything looks stock 968.



Interestingly enough this new diff improved both slow and fast turns. Lap times dropped at Road Atlanta by about 1.5 seconds per lap. Now I very seldom lift for fast turns. Before the back end would get alittle crazy.



You will have to make a sway bar adjustment with this mod because you suddenly have alot more grip on the rear tires. Your front tires are going to want to push because they now think you put a fat tire on the rear.



I stiffened the rear sway bar one notch to induce the front end to bight...IT WORKED.



You will also have a little more tire wear in the rear due to the extra grip.



Good Luck.

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[Jason Judd]

I have the Powerhouse II 3rd~6th gears...they are nice. But, as mentioned my top speed is lowered...Really keeps the engine in the power band.



I believe that top speed is now 151...not that I'm going to need more than that...maybe as my skill set grows, but not anytime too soon.



Jason

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