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914World.com _ 914World Garage _ someone please write a dissertation on LSD's
Posted by: Aaron Cox Mar 4 2006, 09:53 PM
blows my mind... im interested in how each one works, and the effects of it on acceleration (lock unlock etc) for each of them....
would be a great wealth of knowledge to have in one place....
bueller?
Posted by: TimT Mar 4 2006, 09:56 PM
its not rocket science...
Posted by: Aaron Cox Mar 4 2006, 09:57 PM
tim, you can sing about LSD's if thats your style 
Posted by: TimT Mar 4 2006, 10:01 PM
Not sure what your looking for exactly... As LSDs have been discussed ad nauseaum....
Posted by: SLITS Mar 4 2006, 10:02 PM
1. Put tiny piece of designed square paper onto tongue and let disolve.
2. Experience dillusions for up to 14 hours.
Posted by: Aaron Cox Mar 4 2006, 10:02 PM
| QUOTE (TimT @ Mar 4 2006, 09:01 PM) |
| Not sure what your looking for exactly... As LSDs have been discussed ad nauseaum.... |
well make me dizzy....
in one thread.....
Posted by: J P Stein Mar 4 2006, 10:11 PM
The only thing I know about LSDs is that I have had one on order since Nov 11 2005 and still haven't gotten the fucker.
Them Hawaiian gear cutters are doing too much surfin' and not enuff cutting. Supposedly, the next batch should be here about yesterday or the day before........which is still too damn late.......shit.
Posted by: pek771 Mar 4 2006, 10:20 PM
http://auto.howstuffworks.com/differential.htm
The basics. I'm curious about this Phantom Grip deal.
Posted by: Aaron Cox Mar 4 2006, 10:30 PM
| QUOTE (pek771 @ Mar 4 2006, 09:20 PM) |
| http://auto.howstuffworks.com/differential.htm The basics. I'm curious about this Phantom Grip deal. |
just read the whole thing... knew most of it...
now id like to learn about each one's behavior in accel/decel conditions... and cornering
Posted by: alpha434 Mar 4 2006, 10:31 PM
Dude. Where's the young gun action? You have to know two-three times as much as the old guys do. That's the rule.
All limited slips consist of clutch mechanism(s) and a spring to hold the clutch(es) down. This way there is a lot of resistance to slipping. And it will slip when there is a lot of force telling it to, like when turning. And no slip (or very little) when your coming down the straightaway.
The difference between manufacturers is either quality (parts tolerancing and failure prevention) OR novelty (achieving the same effect a different way.) Not usually both.
The phantom grip isn't really a limited slip. It's positive traction. It locks both differentials when there is positive pressure coming from the pinion. And it unlocks when there isn't any pressure. They even sell spring kits on their site to be able to adjust responsiveness, i.e. how much pressure locks the diffs.
A limited slip, posi-trac, locked, or open differnetial drastically changes how you have to drive on the track. If you're used to powering hard through corners, then an improperly tuned Phantom Grip will literally make your car "undrivable." But maybe a locked diff would be ok, because then you just have to push hard enough to break the tires loose.
But now I'm past answering you question and I'm blabbering.
Posted by: alpha434 Mar 4 2006, 10:35 PM
| QUOTE (Aaron Cox @ Mar 4 2006, 08:30 PM) | ||
just read the whole thing... knew most of it... now id like to learn about each one's behavior in accel/decel conditions... and cornering |
Glad you asked.
PG: Can't power through the corners or the diffs will lock
LS: Easy to set proper spring pressure for cornering.
Locked:Have to be able to break the tires loose, or you'll push yourself off the track.
Opem:Best cornering, since the axles are free to change speeds. Hurts you on the straights, where you've only got one wheel driving you at any given time.
Posted by: pek771 Mar 4 2006, 11:01 PM
Regarding the Phantom Grip...
I looked at their website, but there wasn't much info. I'm really not sure how their unit operates. First I even heard of one was today, when XHead (Fiat guy) mentioned he has experience with them.
Also, being old, I seem to recall the difference between limited slip and Posi-Traction is that Posi-Traction is a copyrighted name belonging to General Motors. I don't recall a Ford ever having Posi-Traction.
Pat
Posted by: bondo Mar 4 2006, 11:06 PM
| QUOTE (pek771 @ Mar 4 2006, 10:01 PM) |
| Regarding the Phantom Grip... I looked at their website, but there wasn't much info. I'm really not sure how their unit operates. First I even heard of one was today, when XHead (Fiat guy) mentioned he has experience with them. Also, being old, I seem to recall the difference between limited slip and Posi-Traction is that Posi-Traction is a copyrighted name belonging to General Motors. I don't recall a Ford ever having Posi-Traction. Pat |
Ford had trac-lock as their trademark. Posi-trac and trac-lock are both clutch type. I think alpha is thinking of the "detroit locker" which fully locks on acceleration.. which I *think* is what the phantom grip is a variant of.
Posted by: alpha434 Mar 4 2006, 11:10 PM
Could be. I've actually never worked on an american car.
Posted by: bondo Mar 4 2006, 11:12 PM
http://en.wikipedia.org/wiki/Limited_Slip_Differential
http://en.wikipedia.org/wiki/Locking_differential
Posted by: alpha434 Mar 4 2006, 11:20 PM
Yeah. My definition of posi-trac was hearsay from an idiot. I should've known.
Posted by: Dr. Roger Mar 4 2006, 11:29 PM
one strange thing about lockers is that if you go into a turn and accelerate out, the locker will lock. then your turning can get a little weird if your not used to it. most people stay out of the throttle on slow turns. Or gun it.
LSD set at about 80% is my preferrence.
Posted by: alpha434 Mar 4 2006, 11:33 PM
| QUOTE (Dr. Roger @ Mar 4 2006, 09:29 PM) |
| one strange thing about lockers is that if you go into a turn and accelerate out, the locker will lock. then your turning can get a little weird if your not used to it. most people stay out of the throttle on slow turns. Or gun it. LSD set at about 80% is my preferrence. |
Like I said. You can change those springs to set the response. Tighter springs will make it so that the locker doesn't lock as quickly.
The 80% is usually a good choice.
Everything depends on the track that you're at.
Posted by: sixnotfour Mar 4 2006, 11:38 PM
18 types to choose from;Use the "select diiff. " box and enjoy the selection.
http://reiderracing.com/differentials.htm#
Posted by: pek771 Mar 4 2006, 11:47 PM
It seems the useful combinations we would consider are the open, Quaife type, ZF type and the Phantom Grip. The lockers are impractical, and the track cars would just run a welded rear.
I know there is a difference between the Quaife and the ZF, because I hear the autox guys rave about the Quaife, and the track guys say they suck.
Posted by: campbellcj Mar 5 2006, 12:00 AM
There have been a bunch of detailed differential threads on the Pelican (racing) board in the past few months.
http://forums.pelicanparts.com/showthread.php?s=&threadid=263855&highlight=lsd
http://forums.pelicanparts.com/showthread.php?s=&threadid=256388&highlight=lsd
http://forums.pelicanparts.com/showthread.php?s=&threadid=253907&highlight=lsd
http://forums.pelicanparts.com/showthread.php?s=&threadid=254044&highlight=lsd
http://forums.pelicanparts.com/showthread.php?s=&threadid=251066&highlight=lsd
http://forums.pelicanparts.com/showthread.php?s=&threadid=250845&highlight=lsd
http://forums.pelicanparts.com/showthread.php?s=&threadid=141434&highlight=lsd
etc....
There was a very good (but not flawless) overview in the POC Velocity magazine a few years ago.
http://www.guardtransmission.com/velocity.htm
(I believe the full magazine issue is also still on the POC website in PDF format).
Posted by: KenH Mar 5 2006, 01:51 AM
Arron - not sure I can answer all, or any of your questions, but I can give you my impressions driving with an LSD.
I added an 80% ZF LSD to my 914-4 set-up for the track, but running stock motor & tranny.
The main thing I noticed the car felt far more stable and under control. Situations that would have be "Oh Shit" were only "oops". The LSD increased my confidence in the car and therefor I could, and did, drive it faster.
Depending on the situation the LSD helps keep the back-end under control, sometimes by adding throtle sometimes by backing off, depends on the situation.
Some say there is a minimum engine power you should have before the LSD makes any difference and this may be so when powering out of turns, but the there is no question in my mind the LSD makes my 100hp car better.
I know this is not nut & bolt secific info but I would certainlly hate be without the my LSD.
Ken
Posted by: brant Mar 5 2006, 07:58 AM
| QUOTE (pek771 @ Mar 4 2006, 10:47 PM) |
| It seems the useful combinations we would consider are the open, Quaife type, ZF type and the Phantom Grip. The lockers are impractical, and the track cars would just run a welded rear. I know there is a difference between the Quaife and the ZF, because I hear the autox guys rave about the Quaife, and the track guys say they suck. |
Quaife and ZF work VERY differently.
and I would also argue that the paul guard brand of GT (also a clutch pack) works very differntly in real world application than a ZF, so add one more to the list.
The GT and ZF are both Clutch packs, but the GT allows different ratio's of ramp up/slip on both Accel and Decel, where as the ZF only allows one ratio period. So in real world applications they are very different when used. (although using the same technology to get there)
Posted by: brant Mar 5 2006, 08:24 AM
One more thing..
in a conversation with Paul Guard directly he admitted to me that the standard 911 rule of thumb does not necessarily apply to a mid engined car like the 914.
Its a commonly held belief that the clutch type is better on a track and the Torque Biasing type is better in autox.
However, in low horsepower cars my race GURU did testing and found that despite this commonly held belief they were picking up significant time on track using the same car with the Torque Biasing style.
As you can imagine, this left me confused.
I spoke with Paul Guard about it and he confirmed that there is a difference in application between a 911 and 914 and that the Torque biasing could be better on track in a 914 under some conditions (like low level of HP)
so I'm on the waitlist like JP
The TB does not have clutches and works differently.. very differntly than a ZF style
here is the ATB propaganda:
---------------------------------------------------------------------
The Quaife torque biasing differential enables your car to accelerate quicker and corner faster. How?
By getting the power to the ground!
The Quaife Differential powers both drive wheels under nearly all conditions, instead of just one. With an ordinary open differential, standard on most cars, a lot of precious power is wasted during wheelspin under acceleration. This happens because the open differential shifts power to the wheel with less grip (along the path of least resistance). The Quaife, however, does just the opposite. It senses which wheel has the better grip, and biases the power to that wheel. It does this smoothly and constantly, and without ever completely removing power from the other wheel.
In drag-race style, straight-line acceleration runs, this results in a close to ideal 50/50 power split to both drive wheels, resulting in essentially twice the grip of an ordinary differential (they don't call open diffs "peglegs" for nothing).
In cornering, while accelerating out of a turn, the Quaife biases power to the outside wheel, reducing inside-wheel spin. This allows the driver to begin accelerating earlier, exiting the corner at a higher speed.
The Quaife also controls loss of traction when the front wheels are on slippery surfaces such as ice and snow or mud, providing the appropriate biased traction needed to overcome these adverse conditions. The Quaife Differential provides constant and infinitely variable drive. Power is transferred automatically without the use of normal friction pads or plates seen in other limited-slip designs.
The Quaife's unique design offers maximum traction, improves handling and steering, and puts the power where it is needed most. A definite advantage whether on the track or on the street.
The Quaife is extremely strong and durable and since the Quaife is gear operated, it has no plates or clutches that can wear out and need costly replacement.
The Quaife is great for street driving or racing. Racers don't have to put up with locking mechanisms or spools that created unwanted understeer under power, or in the case of front-drive cars, even tear the steering wheel out of their hands when cornering. Because it behaves like an open differential during ordinary driving, street drivers will have trouble telling it's there until pushing the car's limits.
The Quaife has been proven in everything from SCCA Rally to Formula 1. It provides autocrossers with such an advantage, it has become "required" equipment for a winning effort.
Posted by: kdfoust Mar 5 2006, 03:11 PM
I've made my descision for my big track car (944S2). It's getting a Porsche OEM (ZF type) LSD. In fact it's being installed end of next week. I won't get to shake 'er down on the track until the first part of April but I've got pretty high hopes.
My goal for next week's LSD install is twofold:
1) Better hookup on corner exit (with a trade-off in understeer expected).
2) Better initial turn in (like trailing braking).
My experience with the open diff on that car has been that a very delicate pedalling act was needed to keep it hooked up coming out of corners. It was actually quite enjoyable to do and really fun and quick when I'd get it right with the loud pedal. A little wrong and I'd have over heated back tires and a oversteering beast in one lap.
I talked with Paul @ Guard about my application and I decided that the Guard version of the LSD wasn't worth another $1300 to me (I'd picked up a used LSD for $400 and spent $100 in parts to refurbish it) in that car. The only disadvantage I see between the Guard and this particular version of the OEM LSD is that Guard and Porsche went to asymetrical angles on the thrust rings which can then be setup for different amounts of lock on accel and decel. That sounds appealing but not appealing enough for the difference in cost.
The interesting thing about this LSD install is that the car has been well sorted for about a year and the times on the track are well defined. I'll know what it's worth to me timewise after I re-learn how to drive the car... 
Good luck,
Kevin
PS - Later this year the 3.2-914 will get an LSD as well. What type: I don't know yet.
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