Dougs951S

I have an LSD tranny with < 50K miles on it and a new solid mount. It is in good shape, so I assume it is working well. Is it normal to be able to break fairly sticky tires free in 1st with an LSD tranny? I'm running new BFG geforce sports in 225 and they break free at about 5k rpm when the car really starts to pull, but only in 1st. I'm running a k27/8 and only have boost set at 1 bar because I'm running stock injectors still. I estimate ~280 whp and 300+ ft-lbs at that boost level. I thought it would take more power than that to break them free and I wonder how the 3+ liter guys manage. Or is there something wrong with my diff? fluid was just changed with swepco about 2k miles ago and the fluid that came out looked great.

fortysixandtwo

Your differential is probably fine, but even an open differential will spin both tires, while accelerating in a straight line. To road test it, you will need a traction imbalance, like having one tire on sand, or trying to accelerate out of a corner.

As for the 3+ liter guys; 1st is almost useless, 2nd will break loose at 3.5K with less than half throttle, 3rd will break loose at full throttle, 4th will take full throttle, as long as the pavement is not wet or cold, and I haven't had any problems with traction in 5th, but does feel like its going to loose grip in the wet. This is with an open differential and 245, Hankook RS-2's.

Dougs951S

The diff feels like it works fine, I can feel it do its thing accelerating hard out of a corner. I just thought it would take more power than that to break em both free on dry, warm pavement in a straight line. I guess my question really is how much power should it take to break the rear free in 1st with an lsd tranny?

fortysix, how do you think your car would fair traction wise if it had lsd?

fortysixandtwo

These cars typically spin both tires, when traveling in a straight line, so having an lsd will not make much of a difference in that type of scenario. Whether you loose traction or not, would depend more on the tire and road surface conditions. What will it take hp wise? It sounds like you've about figured out where that is. Back when old school chips and a test pipe were my only mods, that car would not break loose in 1st, once the tires hooked up, so it takes more than about 250rwhp to break them free.
The real gain with having an lsd is being able to apply more power while one tire does not have as much traction as the other, like in a turn or when one tire is on a more slippery surface.

Except for accelerating in a corner, it would be the same.

Dougs951S

very good answers, thanks. I understand how a limited slip works and what it is intended for, I just did not realize that it made no difference at all in a straight line. I would have thought it would at least aid traction slightly in the forward direction but what you said about spinning both tires makes sense. Since our cars have an independent rear end, both tires would have the same or very nearly the same torque on them in a straight line acceleration scenario. If they both break free at the same time, the LSD is acting like an open diff in that moment since there is not a wheel with traction to transmit torque to.

At 18 psi, I sometimes spin in second as well, but I worry about injector duty cycle at these boost levels. I remember reading in a thread somewhere that on a good surface with good tires, it took about 330 Ft-lbs to the wheels to break free in 2nd, about 480 ft lbs in 3rd, and about 660 ft lbs in 4th. Don't know how true that is but I can imagine my car making at least 330 at 18 psi. How much power are you making fortysix?

fortysixandtwo

It will still make a difference in a straight line, but just not all the time. With the open diff, once one of the tires starts to loose traction, its smoke making time. When close to the traction limit, all it takes is a small bump, sand, water, oil, broken pavement, etc.... for this to happen. The lsd will help prevent the tire that's lost traction from running out of control. This will give more consistent acceleration, by making it less likely to fully lose traction. The same goes while regaining traction.

At your hp level, you should be spinning both tires when shifting at full throttle into 2nd. With the lsd, both tires will stop slipping at about the same time. On an open diff, usually one tire will continue to slip after the other has regained traction, reducing acceleration.

fortysixandtwo

I'm running a what we considered an "eh, good enough" tune for 17psi on 91 octane, which put out about 400 rwtq/hp.
Two things to consider:
245 wide tires are skinny for that power level
The tq/hp increases rapidly from 3.5k to 4.5k rpm.

Thom

If I go WOT in 2nd gear the rears will spin until I shift into third gear (beyond 6k rpm) and will keep spinning a very short time as I engage 3rd gear before gaining traction and feeling on the edge of traction all the way through 3rd gear.
While one may expect the rear end to squat under the torque the car feels like it's taking off instead, but I would put this on the account of the very good KW V3 suspension, as with the previous Koni yellows the rear used to squat a lot, and that was with less power.

That is with a factory LSD that works and 245/45/16 Bridgestone S-02.
In the wet the rears will spin with little boost, even in 5th gear, but the LSD allows to realign the car decently when taking some angle, provided driving in a lower gear as a sudden loss of traction may be controlled through a slide only if the engine can be revved quickly enough to provoke sustained and controlled wheel spin... if my wording makes sense?

blade7

225 You need more tyre .

lee101315

So let me get this straight.
Its getting cold out.
You have skinny 225mm wide "summer tires"
You have a K27/8 at 1 bar.

And you expect traction in 1st gear because you installed an LSD?

A LSD will help you drift clockwise ( instead of only counter clockwise ) and put the power down evenly coming out of fast corners under power.

Get some wider wheels and tires ( at least 255 ) and install some soft compound tires. I like Falken Azenis, 615K, but they only last 5000-7000 miles.

Just remember one thing. You can consider traction as a "fuse" for drivetrain components. You might just find that when the tires finally do stick, that the axles dont quite hold up. Roll onto the power gently, dont slam gears, and only accelerate brutally once youre rolling...you'll spend less on drivetrain parts

User 52121

In cold weather (~50 degrees) on summer-rated 285's my car will haze them in 2nd gear at 3500 with a more or less stock motor (~14psi, 3" exhaust, M-Tune). I have a Guard LSD. It will flat-out light 'em up if I'm on my Pilot Sport Cups (IMO a fairly dangerous tire to drive on in the cold, don't try this at home kids!)

In warmer weather (~60-65) on my 225 all seasons, in the right situation, it will do the same.

This is all in *2nd* gear. In each of these scenarios but using 1st gear, it will light 'em up and hit the rev limiter if I'm not careful.

I'd say what you're experiencing is "expected behavior."

blown 944

I couldn't even imagine 225s in colder weather. I bet I could light them up in 5th. I've been driving my car the last few days to work and back and it will drift in 4th if I roll into the boost too hard. Way too dangerous....

jerome951

My car will sometimes break the rear end loose when the boost kicks in 2nd gear running 255 or 275 Hoosier R6s. My car is stock except for a 3" exhaust. What you're experiencing is normal.

mudbuddha

Doug- While this could be normal, it doesn't means that it optimized for your set up or driving style. Having 225 section width tires for the rears are just too narrow especially for a near 300 rwhp car with lsd or not imho. That's a lot of hp for the tires to handle not to mention the cold and or suspension set up. Stock turbo with 220-250 hp came standard with up to 245mm for the turbo S cars and that's crank hp. You are making 280 rwhp so that's what 320 ish to the crank- a big jump and would toast the 225 easily warm or cold and with or without lsd. With a factory lsd, the car will tend to kick it's rear out to the right so be ready to counter steer in those situations. With stock suspension set up, the rear tends to squat, and this behavior will actually helps a little in neutralizing the wheel spin and rear tail kicking out due to the under steer. In any event, I'd go to a wider rim/tires selection as this will give you more room to grow and give you more stability when you apply power in any gear- I'd go to at least 255mm range for the rears if not 275s on 9.5 in wide rims minimum. If nothing else, it will be much safer and allow you to enjoy the car's handling capabilities much better. A lot has to do with driving habits also so, street, track, DE, DD, auto x etc...ymmv, imo

Dougs951S

Thanks everybody for the terrific answers and anecdotes, I love this forum. I guess it is about that time to get wider rims, as this car is only going to keep making more power. I just wish more factory Porsche rims were deep dish. I very much like my set of 86 phone dials, and if I were able to get tires in say, a 9.5 or 10 x 16 with a very short sidewall, I would just pay to have my wheels widened as I like them that much. Guess I will keep an eye out for a good used set of 8x17 and 9x17 Cup II or Cup I wheels and run 245/275. Would anybody be interested in a set of deep dish early offset phone dials in great condition, with new tires?