Aug 252009
 

The following (below the posts) is a response from O.S. Giken regarding the Super Lock that generated from the Viper Club forums:

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Thank you for letting us know about some confusion arising on the internet regarding our OS Super Lock LSD for the Gen 3 Viper.

I will try to provide an explanation to the following postings that contain some comments that may be misleading when applied to

the OS unit:

The Posts:

Quote #1

I am sure they are a fantastic piece of gear, the stuff they make for Skylines is impressive too.

However to throw out a quaife for one on a street car or a road race car I would question – unless you want to drift.

The fundamental difference is that the quaife is not a true LSD – it applies power to both wheels in a straight line, but to the side that needs it most when traction is lost. It is this function that enables more power out of turns because it is applying more power to the OUTSIDE wheel which means to you get power down and can steer the car.

By comparison, once traction is lost with a locked diff (OS Giken under power) you cannot steer a locked diff car on steering wheel input alone eg. out of a corner or when the back flicks out! You have to steer LSD cars with the throttle as well once they lose traction. This is perfect for drifting, great for drag racing (until the car goes sideways) but terribly unsafe on public roads unless you have the feel and skill to match.

For super high powered cars I would be keeping the quaife – much safer – but then I’m past needing to powerslide at 125mph steering on the throttle yelling “yee haa yahoo!”

Still, for LSD applications – I’d bet this OS Giken will be better than anything else.

Quote #2

Originally Posted by gb66gth

In reading the devolpment info, provided earlier in the thread, something was mentioned about how the OS Giken dif. would reduce understeer on entry into slow corners on a road course (not a direct quote). Can someone explain to me how this works, that is the dif having an efffect on the front end of the car? I’m no mechanical engineer so a little help here, please….

Reduced corner entry understeer is not a characteristic of clutch-type limited slip differentials vs. the stock Viper units or a Quaife/torsen. It’ll make it worse. A 1.5-way won’t be as bad as a 2-way or spool though – the “original torque setting” (quote from below) is still greater than zero.

Here’s why- when a car is going straight, all 4 wheels are turning at the same speed. In a corner, the inside wheels are turning slower than the outside wheels. In order to initiate a turn, the outside wheels have to speed up vs. the inside. A mechanical clutch-type LSD resists the creation of this speed delta between inside and outside wheels – EVEN WITH THE THROTTLE CLOSED. An open diff doesn’t do this, nor do the stock viscous units or a helical diff like the Quaife. This resistance makes it more work for the front tires to rotate the car, hence more entry understeer.

All this isn’t necessarily the end of the world, some people like the extra “stability” while trail-braking into a corner. If I were to buy a diff for my car (which is used primarily for autocross), the OS Giken is what I’d choose.

The O.S. Giken Response: The OS Super Lock LSD Spec-S settings allow for a smooth and progressive ramp up in lock all the way to 100% lock. The OS Super Lock is unlike other traditional clutch type differentials in that the unique design allows for almost twice the number of clutch plates. More clutch disks provide more surface area to create more friction, necessary to provide the limited slip effect as well as full lock. Having more clutch plates also means that we can achieve up to 100% lock while using minimal preload on the clutch disks. This preload is what provides the “lock” people refer to when one wheel is off the ground. The preload for the OS Spec-S units is set more to supply added stability, rather than full “one-wheel performance”. The preload is mild enough that it will feel very similar to a stock open differential to the daily driver, until the torque is applied. From that point, the unit will provide a smooth and progressive lock up (in direct relation to amount of torque applied, of course) and keep the vehicle moving forward.  The Spec-S units utilize a 1.5way cam angle, meaning that the ramp-up to lock will be bias to providing a more positive lock up on acceleration and far less on deceleration, where the ramp to lock-up will serve more to stabilize the vehicle during braking/deceleration. In essence, the Spec-S will feel like an open differential that doesn’t allow for unwanted wheel spin when exiting corners or “tail wagging” during heavy straight line accelerating (as the unit will provide progressive locking at equal rates to both wheels due to the centered design of our unit). For drag users, this will translate to greater straight line acceleration and keep the rear where it is supposed to be. For track/autocross users this translates to faster corner exit speeds (progressive lock allows for earlier application of throttle) and more stability during heavy braking. In addition, due to the minimum amount of preload utilized, corner entry is essentially unaffected. Faster times will be achieved.

Both of the above comments posted from users in the forum are not necessarily incorrect, but they are not very applicable to the OS Super Lock, as it is very different from traditional clutch type LSDs.

Both situations seem to be describing the turning characteristics and controls of an OS Super Lock LSD as that of a spool or welded differential, or one of our units specifically tuned for drift (higher preload, faster lock timing, etc…). I hope that with the above explanation, your inquiring customers will understand that this is clearly not the case with the Spec-S settings.

While the above explanation mostly addresses the OS Super Lock’s locking characteristics, it should be mentioned that it also unlocks in a relatively seamless fashion. This is due to the design of our pressure ring, which forms the basis of our lock timing control system. In the scenario you mentioned of a customer potentially loosing tire traction and control due to premature lock (likely due to an over-application of torque vs. capacity of the tires when trying to make a turn at an unfavorable angle), if the customer simple lifted off the throttle or up-shifted (thus lessening the application of torque to the wheels/differential) the differential would unlock and allow for the vehicle to regain control via steering and throttle input. Granted, we do not advise any users to practice this on the street!

If any of your customers or Viper owners have any questions regarding our unit, please feel free to forward their questions over to me or have them contact us via our website at www.osgiken.net. We are always happy to spend time with customers and will answer any questions they may have.

Thank you.