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Which LSD is best?

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Old 07-16-2003, 06:23 PM
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Which LSD is best?

I have a question to all you performance performance addicts here. The lack of LSD in my 6MT sedan at times brings tears to my eyes, especially on tight turns. So, I'm going to put in an LSD. I checked with infiniti, and the coupe LSD is $1,800, far too much money. The 350Z LSD costs less. Both the coupe and 350Z LSD's are the viscous type, but both should fit in the sedan. Kaaz makes a cheaper LSD that fits in the 350Z (and I hope G35s) which is the clutch type.

In terms of performance, what are the upsides and downsides of different LSD types? Is there a best overall approach? Also, mechanical LSDs, such as the cluch type, come in 1.5 way and 2way variants. What is the difference?



2003.5 6MT Sedan. Carribean Blue / Graphite
Old 07-16-2003, 10:09 PM
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Re: Which LSD is best?

If you haven't seen or read it, their's a FAQ post you should read.

http://setemail.ru/forums/showfla...sed&sb=5&part=

The stock LSD being a viscious unit has a limitation in the amount of power and or traction it can pass and still do it's job. Stickier tires can even find it's limitations, providing more grip resistance than the viscious fluid can handle. This is why the Kaaz clutch type system is superior, when you load it more, wheather with gripper tires or more power, you compress it's clutch's more, improving it's internal grip level's more. This is the fundamental difference between a clutch-type and a viscous limited slip. The stock viscous diff responds to a difference in wheel speeds, relying on the slipping plates to heat the fluid and tighten, which means it must react to wheelspin AFTER it begins. The KAAZ clutch type responds to torque, so it reacts BEFORE the inside tire has a chance to spin. That's a big differance.

1 way, 1.5 way and 2 way limited slip diff's are talking about if the limited slip action works on just acceleration, acceleration and half on braking (the .5 bit) or both way's (2 way). The KAAZ unit is reported to only be a 2 way. But I know the web site I list in the in the FAQ section does show a 1.5 way to. (BTW, most consider the 1.5 way as the best).

The catch with a clutch type LSD is the fact that they are noisy in operation, the clutch's don't last for ever, (they're wear item). And they require you to change the diff oil, some say at 15k, others say much sooner at 3k.

Only reason I don't have a the KAAZ unit on my sedan is because of the "catch" with clutch type LSD's and I discovered that the 350Z springs and struts I have on the car significantly improved my inside wheel traction to the point that the lack of LSD rarely shows itself on my car now. Car is so much more fun at the limit now.



Ivry 6mt sed
Injen CAI, 22" resonator
8X18 Enkei RPM2 45mm
Kumho MX 245/40
clear corners

<P ID="edit"><FONT class="small"><EM>Edited by ryoken on 08/20/03 08:39 AM.</EM></FONT></P>
Old 07-16-2003, 10:57 PM
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Re: Which LSD is best?

Thanks for the great info, but I have a followup question. I understand where the clutch chatter comes from, but when exactly does it happen. Does it happen in turns all the time or is it dependent on the power going into the diff? I imagine that it shouldn't chatter at all in straightline driving (unless there is wheel slip). Here's where my imagination fails me. I know the clutches will slide against each other whenever I turn. If I apply a lot of power, they will do a lot of work to prevent the wheel speed difference, so I imagine they will chatter a lot. Now, when I'm driving sedately, basically applying only enough power to maintain speed, the clutch plates should be producing very little force; will they chatter in this case? If the diff only makes noises under hard driving, I'm quite fine with that.

2003.5 6MT Sedan. Carribean Blue / Graphite
Old 08-20-2003, 12:11 PM
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Re: Which LSD is best?

Hi:

The type of LSD also put a bug in me, so I searched the net for various info. Seems that the Viscous LSD is marginal at best. Probably just a cheap way of putting in something that they can call an LSD. Note that previous Nissan models used Helical LSD's which are supposed to be really good.

Viscous-type limited slip differentials:

A viscous-type LSD uses a thick fluid sandwiched between plates, one plate being connected to (drives) each wheel. When a rotation difference occurs between wheels, the faster plate spins the fluid which in turn spins the slower plate, hence transferring power from the faster wheel to the slower wheel.
Viscous units have two spinning disks that face each other. Each has a vaned surface and there's a viscous (oddly enough) fluid between them. The fluid has the property that shear forces thicken it. As long as the two disks spin at relatively similar speeds the fluid is "thin". When there is a differential between the two, because one wheel is slipping or you're going around a corner, the fluid is sheared and thickens. The thicker fluid loosely couples the two vaned disks thus limiting slip. Viscous LSDs generally provide something like 20-25% coupling efficiency.

A viscous-type LSD has the advantage of requiring little to no maintenance, since the fluid never wears out. However, from a performance standpoint, a viscous-type LSD is not ideal. On a viscous LSD, it takes a split-second for the LSD to react to slip as the fluid must speed up before it starts turning the slower plate. On higher horsepower cars, any lag in response resulting in uneven traction is especially undesirable.

A viscous-type LSD is often used as the center differential on AWD cars, where the delay in the transfer of power (from front to back) is not as critical. It is also often used in OEM applications where cost, ease of maintenance and quiet operation is important.

In Miata’s, Viscous LSD's are notable for failures at your 145K milage with moderate to hard usage.

Clutch-type limited slip differentials:

A clutch-type LSD uses a set of clutch discs, that are connected to each wheel, and the discs are clamped together at a certain pressure when in operation. When one wheel tries to rotate faster than the other wheel, the clutch discs start to slip, the faster disc transfers power to the slower disc through friction, hence transferring power from the faster wheel to the slower wheel.

A clutch-type LSD responds immediately to any slippage, unlike the viscous-type LSD, and is so better from a performance standpoint. A clutch-type LSD is also much more easily upgradeable to handle high horsepower, as the number of clutch discs can be easily increased or the clutch disc sizes can be enlarged. Most aftermarket clutch-type LSDs have larger/more clutch discs. The downside with a clutch-type LSD is that with the slipping of the clutch discs, they eventually wear down and will require maintenance. Also clutch discs will chatter when they are engaged, so a clutch-type LSD is not as quiet as other LSDs.

Clutch type LSDs are often offered as 1way, 1.5 way or 2-way. A 1-way LSD only engages the clutch discs only on acceleration. The 1.5-Way L.S.D. means that when the car is braking, there is little L.S.D. effect. A 1.5-way LSD is a compromise between a 1-way and 2-way, as it engages the clutch discs with less pressure on deceleration, which allows for more slip on deceleration and hence less oversteer. A 2-way LSD engages the clutch discs on both acceleration and deceleration; the 2-way L.S.D. is always active. If the clutch discs work to limit slip on deceleration, they can optimize traction under braking, but at the same time as they transfer power from the faster wheel to the slower wheel, this increases oversteer in turns. Therefore a 2-way LSD is generally considered more difficult to handle, but superior for handling, while a 1-way LSD is more forgiving.

Note: a viscous LSD is always 1.5 or 2-way by design.

Note: Mechanical LSD’s require proper break in. A mechanical clutch LSD is noisy and better suited to full competition use.

Gear-type limited slip differentials:

Another type of LSD works through gears to limit slip. These LSDs can offer very immediate response like a clutch-type LSD, with little maintenance and quiet operation. However, there are not as easily upgraded for high horsepower as with the clutch-type LSD, they are limited by the strength of their gears. Gear-type LSDs are also generally a lot more costly than the clutch-type or viscous-type LSDs.

Helical LSD:

Manual versions of the Nissan 2005X are fitted with a helical limited-slip rear differential, as fitted to the V Spec Skyline GT-R coupe. Under acceleration, the helical LSD provides faster traction control than a conventional clutch-type LSD or viscous LSD and without relying on the performance of the Viscous Coupling oil as used in a Viscous LSD. Basically, the Helical LSD generates torque to both left and right rear wheels by frictional force between the gear teeth and the differential case.

If one wheel loses traction and tries to spin, that axle's side gear rotates slightly faster, so transmitting the lost torque through the helical gears and back to the differential case. The engine torque is also applied to the same part of the case through the final gear so it in turn drives the road wheel through its side gear.

Honda equipped the Integra Type-R with a helical LSD, which is a superior type of LSD that does not incur power loss compared to the normal viscous coupling LSD

The helical LSD tranny of the Nissan SE-R Spec-V allows the front wheels to rotate at different rates while still applying torque equally, reducing understeer in the corners and allowing you to grab gears on the twisties and apply the throttle in turns sooner with more control.



Torsen LSD: (Torsion sensing LSD)

Torsen, which stands for torsion-sensing, LSD's use gears and typically provide more like 75% coupling. The MRT Torsen style front LSD locks under load so provides more grip when exiting a corner, but acts like an open diff under trailing throttle so it does not induce understeer coming into the corner. This is the major difference with a mechanical LSD. Most rally and full race cars use clutch pack diffs as a Torsen LSD is unable to transfer torque if there is none, ie if the wheel is off the ground it will not work, a clutch diff will. A Modena Torsen LSD is a non-adjustable unit that in theory transfers torque from a spinning wheel to the other wheel before it spins.

Point to consider - a torsen LSD, has silent operation and is ideal for street use.



Some Aftermarket LSD Manufactures






Old 08-20-2003, 12:43 PM
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Re: Which LSD is best?

The helical LSD seems to show up on FWD cars (Maxima, 200SX, etc.) Is there something in it's design that limits it to, or makes it idea for, FWD applications?

2003.5 G35 Sedan Desert Platinum/Graphite Premium/Sport/Aero/Nav/Winter
Old 08-21-2003, 04:19 AM
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Re: Which LSD is best?

The older Maxima and I30 were using hlsd the 04 is using vlsd. vlsd is suppose to be one of the best in the market.


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350z, clutch, deceleration, differential, g35, helical, infiniti, lsd, maintenance, sed, sedan, torsion, type, viscious, viscous
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