jthwan22

How much better is this LSD compare to factory LSD? I think I have factory LSD but with very low lock up torque. The back wheel will spin the same direction when it is up in the air. If I hold 1 back wheel stationary I can spin the other rear wheel with my hand. That is why I think if I have LSD it must not work very good.

Carl Fausett

I'll answer with this quote from Eddie Bello:

"I have tried many differentials in the past with my car, let me tell you, there is nothing that can compare to the OS Giken diffs. Driving a 1200hp rwd car on street tires is a challenge. At my last event before I changed to the OS I was using another brand diff. the car would walk side to side violently, I lost control and did a 360 at nearly 130mph and went into the dirt off the runway. A few weeks later we went out to the texas mile with my new OS differential. I ran the car on street tires again but the car stayed straight as an arrow the whole run and was very controllable. I backed up my world record pass on less boost with no drama during the run. OS giken is the only brand of differential I will run in my car, its been race proven and I stand by them."

-Eddie Bello
Worlds fastest standing mile Porsche 236.6mph
Worlds fastest Porsche ¼ mile 9.1@162mph

Let me also say that I believe vehicle manufacturers are cautious with their limted-slip setups so that a inexperienced driver does not get throttle-induced understeer should they accelerate too hard in a corner. For this reason, they are set up for more slip than grip. In the reverse, on corner entry deceleration, again the manufacturers have to weigh performance vs safety and it comes out their primary goal is keeping the most novice of drivers on the pavement in spite of themselves.

As HP increases (like you have done with your SC kit and as represented in the Eddie Bello quote above) these high-slip diffs can now be causing vehicle instability instead of insuring it.

Better bite, greater vehicle stability in any throttle transition (accel and decel) and lower transaxle temps are just some of the benefits.

GregBBRD

Eddie Bello has a drag race car. Most drag racers use a spool, but that causes really big problems when an axle breaks or a tire slips. Not many of us are drag racing our 928s, so is a 100% locking factor an advantage or a disadvantage once you are not drag racing?

You talk about significant temperature reduction in gearbox temperatures. Obviously, that is the result of reduced slip., which is reduced friction, which results in lower temperatures. However, the speed differential between the two tires are constantly changing in a road race vehicle....which means there has to be slip. One would have to conclude that if the amount of slip is reduced, significantly enough to reduce the oil temperature, that the limited slip is either not slipping at all (no lock), or that the differential is "locked" up and there is one or the other tire "dragging". There's really no other way for the temperatures to be reduced.

Which one is it....and when does this happen?

I know, having been personally involved. that the Porsche and Guard people have worked extremely hard on the "proper" amount of lock-up that is needed for corner entrance and corner exit, on a road race car. The "rate" at which this "change occurs" is also very important.

The "original" Porsche limited slips that Porsche used for road racing with "variable" lock-up under de-acceleration and acceleration were 20/100. These were awful! Extremely difficult to drive and get good results. There's been about 12 different "iterations" of this "basic" design...by Porsche alone...and they are fairly "heavy" into the engineering aspect of these units....and the "Cup Car" program certainly gives them a lot of data.

What assurance do we have that this unit, with no testing in this application, will function well on a road race track? Again, I personally know of no one, out on this coast, that is running one of these differentials in a road race car....so I can't ask this question to anyone who uses one of these units.

BTW...several importamt questions not answered in my first posting.

How long until you get one to test? Are you going to put a decent driver in the car to test and give feedback? How long after that will customers get one?

Carl Fausett

Asked and answered:

I am not prepared to say who will be driving the test vehicle at this time.

Based on the well-documented success of the OS Giken diff in many Porsche gear boxes, I am sure that the 928 install will also work as planned.

You seem to be suggesting, Greg, that the 928 LSD is special and somehow very different than all the other Porsche's. And therefor just because this LSD works well in other Porsche models, it may not work well in a 928.

I do not agree with you. Everything I see in the 928 differential is fairly standard stuff - nothing special at all. I am confident that when fitted, the OS Giken diff will work very well for the 928.

Carl Fausett

I just took my first order for one of these OS-Giken Super-LSD's. One of our good customers grabbed one up. 5 to go!

I will accept no money at this time for these units (then there are no worries of refunds in case the minumum order of 6 does not get reached.)

If an when 5 others are sold, THEN I will need payment to send in the inital order for 10 units.

BC

No, what he is saying is that each chassis, engine, power level, and transmission and handling envelope requires effort to make everything work together. And the LSD is an integral part of both pre-corner braking and turn in, as well as mid and late corner acceleration and power-on steering. He is suggesting the testing of the unit would determine which disk types are used, lockup ratios, ramp ratios for unlocking under braking, etc.

Hell - Formula one in 2012 has differential and "limited slip" controls on the steering wheel that are changed multiple times A LAP - which means with all their millions they cannot make a unit that does everything all the time. This technology is controlled, but in its limited slip (traction control) nature - not lockup.

U-928

Why is it that it seems no one in the porsche community wants anything to do with gear type LSD, like Peloquin or Quaife's? What's the big turn on to clutch type ones?

BC

Great question.

Some info that may or may not help or even mention gear-type LSDs (not for racing use supposedly)

http://grassrootsmotorsports.com/articles/whats-diff/

http://en.wikipedia.org/wiki/Limited-slip_differential

GregBBRD

Hmmm. Reading comprehension apparently low. Let me try again.

I'm not saying what you have suggested, above, at all.

I'm saying that the high performance differentials that Porsche has developed, since the 928 differential was created (which "resemble" this differential that you are trying to sell) are very special and have required extensive development and design changes to get them to work properly. The early "versions" were truly "wicked" (and are essentially door stops) and they have gradually made changes...some radical....to make a differential that works properly under braking and acceleration. Which, as I pointed out, is of utmost importance on a road race vehicle and essentially nonexistant on a drag race vehicle.

This "development" has been very time consuming, due to the amount of testing required to test the changes....however, they have had the "Cup Car" program to help judge the changes. I have no idea of how the people that make "your" new differential have done their testing. Certainly not in a "Cup Car", in which a different differential would be illegal, by most everyone's rules.

Worth noting, as an additional new bit of information, is that as the power output of the "Cup Cars" increases....different differential designs are required. The differential in an RSR is completely different that the differential in a "Cup Car"....due to the additional power output.

Of course, any "variable" locking differential installed into a 928, is going to be subjected to a different set of variables than if it was installed in any other vehicle, simply because of the effects of the rear suspension. The rear suspension toe changes (rear caster, if you will.....called "Kinematic" on a 993) are going to effect/delay the load that makes the differential locking ramps work. This adds further complexity into the equation.

So, yes it is possible to buy a "trick" differential, install it into your 928, and get "worse" performance than a "stock" differential.

Of course, as mentioned above, higher horsepower output, will have a huge effect on how the differential reacts. And as suggested in my prior posting, driver "ability" will also play a huge part in how the differential reacts.

A driver of your abilities would be virtually worthless to test, versus a driver with higher abilities. And, someone like Mark Anderson, who is completely "insensitive" to even large changes in a vehicle's set-up (Mark can drive a complete pile of crap fast, but can't tell if you just turned the shock valves completely a different way.....it makes no difference to him....he "simply" compensates without thinking about it) would also be worthless. To test suspension and differential changes, in a vehicle, you need to come up with a driver that can understand and feel the changes that are made, giving you feedback, as you make changes. And the testing needs to be done in a "back to back" manner. Someone like Kelly Collins, comes to mind.

Otherwise, you just end up with a product that really is an unknown. "Yeah, it works great because I had it made" seldom gets anyone very far.

The "problem" and the "solution" are way more complex than just calling someone up and getting them to build something. This requires "testing" long before it is offered for sale....unless your "testing" methods are to simply make it and sell it....but you'd never do anything like that, right?

Mike Simard

In road racing, pros use clutch type diffs like the stock Porsche. It has the best tunability by changing ramp angles and that can make real differences. Most of the gains can be found in throttle off locking and using that to turn in.

The gear types seem to be good for OEMs because they are trouble free and don't creak.

I don't know why there are any aftermarket gear type diffs at all, it's annoying when you need a diff and that's the only thing available.

Bob Rouleau

Greg, FWIW, it is well know that the OEM LSD in the GT3, RS and Cup cars has a very short life. On the order of 20 track days. Anyone serious changes the innards to GT-Gears stuff, some change the whole diff. This only to say that Porsche OEM limited slips fail to impress the GT3 and Cup car community and at least in these cases aftermarket is a big improvement.

BC

What is the GT3 man over in here for? Slumming it? Getting mixed up with the rif-raff?

Carl Fausett

I'm just trying to bring a LSD to market to fill a void where 1) we cannot quickly get good used LSD's anymore; and 2) some of us are way over the top in torque of what the stock LSD was designed for.

Greg, you act as if I am designing it. I am not. I let the pros do what the pros do, and believe me the guys at G-box and OS Giken know way more than I do about transaxles and LSD's in road racing vehicles.

I make it a point not to hire an expert and then tell them what to do. I've seen it done with doctors, lawyers, and engineers and it rarely turns out well.

I'm sorry I cannot answer all your design questions. Maybe I can get my partner, Erik at G-Box to log on and answer a few. I will ask him tomorrow if he will do that for you.

GregBBRD

The latest "iteration" of the "Cup Car" limited slip is one of the main things that makes these cars so much quicker than the same cars, just a few years ago. Look at what has "happened" to lap times at Daytona....when the "cars" are "fresh" and "unmolested". Compare the percentage of change at this "early in the year" track event and then look at the percentage of change at the tracks run at the middle/end of the year.

Porsche found that the "smoothness" of the lock-up and the release between off throttle and on throttle was very, very important.....in order to not "upset" the car when working near the limits. Any "jarring" of the rear tires, once a "slip angle" has been established, is going to reduce the cornering limits of that vehicle.

Porsche doesn't employ many "fools".

I'd submit that the clutch discs in these differentials is an integral part of that smoothness and putting in a more "aggressive" disc may not be the fastest way around a race track....

GregBBRD

That would be great!