Damien Cort

I'm a bit new to 951s at the moment, I want one, and am in the process of doing my homework. I have a couple of questions:

1. Did all 951s come with lsds? If not, which ones and which years?

2. Is the 951 tranny (l16r) a 5spd manual, or a 4spd w/ OD? Also, what kind of power can it take?

Thanks for any input.

adrial

1988 951S's and 1989 951's came with LSD stock, along with an oil cooler. (89 951 same as 88 951S, minus the S)

'86 came with oil cooler standard.
all other cars oil cooler & LSD were options..

951 tranny can take a lot of power...the big hp guys have been running 400-500RWHP without tranny problems as far as i know...

It's a 5 speed manual...

Tom Pultz

You can't separate them by years. All you can be sure of is that all '88 944 Turbo S and all '89 944 Turbo cars came with LSD. For others, check for option code 220. Most of them did NOT have LSD.
It's a 5 speed, but 5th is an overdrive gear with a 0.82 ratio as I recall.
Enough

Damien Cort

Cool, thanks for the replies!

Luke

Sheeeesh!! tell that to my tranny! I knocked several teeth of my second gear.



call me odd.....but I perfer the open diff's any way~

Jeremy Martin

just fyi, my 86' 944 turbo has LSD and an oil cooler

Danno

I recommend getting a torsen LSD like a Quaiffe or Guard unit. I think GPR has a special on the Quaiffe right now at about $1200 or so. Check the ads in the back of Excellence.

Steve Lavigne

I've heard that the torsen transfer torque smoother than the clutch based lsd. I was considering picking up a used oem lsd for my 951, changing the lockup %, and installing it in my transmission. Did you have an oem lsd before your torsen, and if so, how does it compare?

PrerYDoG

I would not consider are 5th gears to be an OD gear. Drive a Mustang GT, put it in 5th and try to accellerate. Anything happen? Nope, nada. That's OD. Put our cars in 5th gear, hit the accellerator and try not to choke on your own spit as it flys to the back of your throat. That, that is not OD.


Mark

Luke

I guess the current SVT cobras can pull 153mph in 4th and only 142 in 5th !! (buddy has a 99')

Russ Murphy

You know, I've heard it from a couple of different of folks with extensive 951 racing experience that LSD's aren't the way to go if you want to go really fast (on the track that is, not at the drag strip).

So how 'bout that Luke.

Steve Lavigne

So you're saying that solid differential is the way to go for road racing a 951? Or, you are saying that open differentials are the way to go?

Steve Lavigne

Ok, I figured out what you are talking about. Instead of outdated limited slip differentials, the best way to go is with an electronically controlled clutch based differential which can actually replace the engine/gearbox clutch. This is of course ala Ferrari F1; so new that they won't have it till a few races into the 2002 season. Yeah, those 951 racers are right, this would be a better way to go.

Danno

The people who said that LSD aren't good for fast lap times probably are using the stock Porsche friction-plate LSD. They may even have increased the spring pre-load to a higher value, effectively making their rear-end a solid-locker until high torque-differences exist. This causes a lot of understeer and slow lap-times.

With the friction-plate LSD, your tranny is really locked-diff (50/50 torque-split, zero rotational differences). Sure this really helps in slow-speed tight corners where it's easy to spin the inside tire under power, but on high-speed corners where traction for power-delivery isn't a problem it causes understeer.

Then in middle-speed corners, where it's a balance of power-delivery and cornering, the friction-plate LSD will transition between 50/50 locker operation to limited-slip torque-splitting, to fully open-diff slipping. And back again. This causes the rear end of the car to shift back & forth and break traction several times in the same corner. This is probably another reason, those folks Russ talked to didn't like LSD for track use.

Good example is the long turn-2 at Willow Springs. It had the perfect curvature where at the cornering limit at 80-90mph, you could also almost dial in full throttle as well. With the stock friction-plate LSD, it would switch between friction-plate slipping (torque-splitting) mode and open-diff mode (when power applied was too much for it to handle). This caused the back end to step out about 6", then the inside rear tire would spin. This would then reduce my speed and cornering speed and the LSD would then switch back to friction-slipping mode and the car would start accelerating again. But it was really annoying going around that corner with my back end wagging back and forth because of the action of the friction-plate LSD was so abrupt.

Going to a Quaiffe torsen-LSD solved all that. It continuously splits torque 50/50 in straight line modes, all the way to 100/0 smoothly without any sudden shifts. It also allows just about any rotational differences between the tires as well so you don't have a stuttering back end when trolling around parking lots or the pits (unlike the 80% lock-up friction-plate LSD).

One perfect demonstration of the differences between the various diffs can be illustrated by doing a drag-race style start with one rear tire on pavement and one rear tire in the dirt. With an open-diff, you'll just spin the dirt tire and not much happens except for slow acceleration. With a friction-plate LSD, initially for a fraction of a second, you'll have acceleration, then a lot of chatter from the gear-box and tires as the diff. goes from 50/50 torque-split into the friction-plate slipping torque-splitting mode. Then the dirt tire will just spin because the torque differences are too great for the slipping clutches to handle.

With a torsen-LSD, you can just stomp on the gas and you'll get a smooth launch that's almost as quick as with both tires on pavement. The torsen will actually split so much torque that you'll have enough power applied to the tire that's on pavement to spin it, and at the same time, not spin the dirt tire uncontrollably.

These LSDs were de-riguer for F1 racing back in the late-'80s and early-90s. They have only been surplanted by computer-controlled diffs. because they can use rear-steer with them. Since that's been banned, F1 teams have gone to using the brakes for traction-control, but the resultant actions and torque-splits are gradual, just like the torsen-LSD.

I've got several articles on the torsen-LSD on my website: 951 RacerX website

Dan87951

I have a Gaurd torque biasing diff in my 2nd car and it has held up well. I believe it was $1295. What makes them so superior to the factory units is it has not clutches. They are all gear done. Really nice unit I think! It sure does hook up well.