VLSD - your opinions

[Ejkej]

Hi!

First of all:

I went a different way than most of You guys go when choosing a diff swap.

I decided to use subi R160 diffs, as R180 are difficult to buy and rather expensive here. I was hoping that R160 will endure 200 BHP engine... unfortunately it did not.

The spider gears are the weak point, just as written in the FAQ section, so I found a SVX subaru diff (vlsd) with rear axles - and I think that it solved the durability problem.

 

When dry the car was much more predictable and I was very happy - I felt that I can control the oversteer with throttle - I didn't feel that way with open diff.

However the problem occured on a wet, slip surface - when decelarating the car suddenly started oversteering in a very abrupt way. I know the conditions on this track and was trying to drive defensively, but even a slight lift of a throttle caused a spin out.

 

Yesterday I spoke to a guy who said that a 2-way LSD in a RWD car is very difficult to control - especially when wet.

What do You think? To be frank, now I am afraid to take my Z for a drive on a rainy day - I was so astonished with how the car felt... I really don't know if it is safe.

 

BTW, below the video where You can see the spin outs: 0:11; 0:53; 2:36; 3:02.

 

 

Thanks,

Andrzej

Edited October 15, 2012 by Ejkej

[Z Greek]

Wow, That's pretty dramatic. I run a WELDED R180 4.11:1 in an endurance car (Chumpcar), and it is very predictable. Oversteer can be induced very easily with throttle, but I have not noticed the violent off throttle oversteer your car seems to exhibit. The car has about 40 race hours on it, but we have not run it in the rain. I have spun the car a couple of times, but it was a combination of off throttle, and too abrupt braking (my fault, rookie mistake).

What tires are those?

Were other cars spinning?

Personally, I would not be so quick to blame it on the diff., but others may have a different opinion. I plan on using a Subie VLSD in my street car.

[NewZed]

At 2:36, it sounds like the diff's locking function wasn't even being used. Sounded like neutral power to the diff on the audio, no decceleration, no acceleration.

 

The sliding looks like my car right after I got it running and drove around on wet streets with 10 year old tires.

[Ejkej]

As for the welded diff - my friend claims the same - he has no problems with predicting the car, but maybe the reason is that with welded diff you have constant power on both wheels...

With VLSD everything was OK until slowing down. I am the last one to blame the diff for my performance - my first thought was: OK, I need to learn how to drive this thing, but the opinion on 2-way LSD comes from a person who has major experience with rally drivetrains. Now I need yours.

 

Other cars were spinning as well :

 

 

But I drove there before and had rather problems with understeering - caused by conditions and speed.

I am also wondering if the final gear ratio can be a partial reason here, with 3,90 open diff I had no such problems. Now I run 4,44.

 

The tires were Yokohama AD08 and after 1 run (when it became obvious that it will rain) - Uniroyal Rainsport2, both in very good condition, both with low pressure, also the rear sway bar was unbolted after 1 run.

Edited October 15, 2012 by Ejkej

[Daphur280]

Did you get the svx diff to work in the Z?

Edited March 7, 2013 by Daphur280

[johnc]

Its not your diff.

 

Every spin except the second was driver induced - you're over driving the car based on the conditions and your suspension setup.  The second spin was caused by the bump in the turn.   Your car appears to have very little bump travel and not enough rebound control for the springs.  It just kinda hops around and this hopping unloads the rear suspension just when you're applying power.  You also have an under steer problem that causes snap over steer.  When the front plows you lift which transfers weight forward, this loads the front wheels which gain grip and start turn in the direction the wheel is pointed just when the rear gets unloaded and then breaks loose.

Essentially your car is under damped and have you have a front grip problem (under steer).

[Ejkej]

@ Daphur:

Yes I got the svx diff work with my 280z.

In short:

I redrilled holes for the 280z drive shaft in the subi diff flange, I drilled 2 additional holes in the mustache bar for narrower R160 rear mounting and used additional spacers between the mustache bar and diff cover. Also I nedded to machine the svx axles to match the stock 280z ones:

 

@ johnc:

thanks fo answering John... I have koni race inserts on 4 corners with eibach 250 springs. Do You have any suggestions on how to try to setup such a combo? As far as I remember I tried to use tips from "how to" by beta motorsport (which I think was attached to the Konis)... I know it is a complex process, but...

[johnc]

Where is the adjustment on the Konis?  How many turns out from full soft?  If you have 250lb/in springs on all four corner you might be getting some pitch oscillation.  Try upping the front spring rate to 275.

[Ejkej]

The adjustment is on top only. They have ca 1,5 of a total turn from soft to hard.

I had them set up on full hard in front and about 2/3 of a turn in rear.

[johnc]

If the shock is the Koni 8610 then you should have 2.5 turns from full soft to full hard.  You should be .5 to 1 turn off full soft for those spring rates if the shock is a 8610.  How much bump travel before you hit the bump stops?

[Ejkej]

You are right, it is 2,5 of a turn. As for the bump travel - I will check it and let You know.