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S15 Viscous and Helical Diff

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Can anyone here explain to me what are the different on these two diff..?

I have tried a search but couldn't really found the answer..

My car is a Spec S with Open diff...and today I have picked up the Viscous diff from Spec R Auto...Is it a good upgrade for Spec S or I shouldn't worry about Viscous type and go for Helical?

The ratio for Viscous here is 3.9 by the way...

Cheers
 
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A viscous diff wont fully lock, it needs to be warmed up before it will work. Helical will lock straight off, but both are a good upgrade from an open diff!
From what I've heard the auto diff have a lower ratio than the manual diff which woiuld improve acceleration but may decrease top speed slightly..
 
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Thanks for the info mate...so it is a good upgrade for daily drive?
and as for the ratio..I thought the auto diff has higher ratio of 4.1 whereas Viscous is 3.9
 
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I'm not entirely sure what diff I have in my Spec S + DET, but I know it's a fricken tight LSD and it makes one wheel shudder going around corners in second gear speeds. It's awesome to play with but not ideal sometimes because passengers think it's me bunny-hopping the clutch :/
 
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A viscous diff wont fully lock, it needs to be warmed up before it will work. Helical will lock straight off, but both are a good upgrade from an open diff!
From what I've heard the auto diff have a lower ratio than the manual diff which woiuld improve acceleration but may decrease top speed slightly..
A viscous diff will lock cold or hot and once its worn out it will hardly lock at all you will just wear it out quicker by skidding it up cold, a helical will never lock fully or be open fully,
A viscous LSD is driven by a viscous fluid. The two halfshafts aren't directly connected, instead they have fan-type things inside this viscous fluid, when the two wheels are spinning the same speed, both the fans and the fluid are all spinning together. When one wheel starts to spin faster than the other, it creates an imbalance in the LSD, the slower wheel wants to speed up and the faster wheel wants to slow down because of the fluid. On a hard launch you won't be able to tell any different between a car with an open differential and one with a viscous lsd until one wheel breaks loose, on the viscous car the power will transfer to the wheel that isn't spinning as fast, and on the open differential that one wheel will just keep on spinning how it wishes.

A Helical uses a series of helical gears around two central gears, simply put it means you are always getting drive on both, just not 50 / 50 split, it varies the power to either side depending on application which is why its so good for things like road or targa use, but kinda crap at drift. And no you cant shim a HLSD as it does not use clutch packs or viscous fans to achieve lock, its just one hell of a hard arse solid diff, used in the GTR, Supra and a whole lot of other cars and a lot of off roaders.


If you are going to put the viscous diff into your spec S then i would highly recommend you just put the head in and keep the ring gear from your open so that you don’t lose your current ratio, while you are at it, shim it up tight as so it locks quickly and you don’t get too much axle tramp.
 
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I'm not entirely sure what diff I have in my Spec S + DET, but I know it's a fricken tight LSD and it makes one wheel shudder going around corners in second gear speeds. It's awesome to play with but not ideal sometimes because passengers think it's me bunny-hopping the clutch :/
could just be a v lsd thats had the the crap shimmed out of it so it acts like a 2way only rougher, if you open the case you might find you have a aftermarket one like a nismo or something, bonus. Or if you go for a WOF and it fails on the diff they might think you have a welded one :) remove the fill bung and look in there with a torch to see what the head looks like, if you see a whole heap of welded up metal i would look at changing it, or it could just be a vlsd if you are not sure what a R200 Vlsd head looks like just google it
 
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Sweet, cheers. I might give that a go later. I'm 90% sure it's not welded though.

Just checked the listing I bought it through and he said it's a Viscous LSD. My bad, could have done that before
 
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I may try to sell the Viscous diff and get Helical ones instead..as I have looked around on different forums..people tends to go for Helical ones for street.
do you know how much the viscous worth these day? 100 bucks?
cheers
 
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Sweet, cheers. I might give that a go later. I'm 90% sure it's not welded though.

Just checked the listing I bought it through and he said it's a Viscous LSD. My bad, could have done that before
If its a viscous that clunking around intersection corners its just been shimmed really really really tight, keep it as it will be good for drifting for awhile until it wears itself out, just tell your passengers that its just the way it is
 
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I may try to sell the Viscous diff and get Helical ones instead..as I have looked around on different forums..people tends to go for Helical ones for street.
do you know how much the viscous worth these day? 100 bucks?
cheers
do you want to have a go at drifting or just good grip on road use?

ill buy the viscous one off you for $100 providing its not stuffed, would be a good skid diff for track days.
The helical is good for grip, and you can still do two wheel skids, i peeled out a set up cheapy skyline wheels the other day, and the marks up the track were even until you start going around and around :) . its just not easy to control going around a track sideways, in my old spec s with the helical in it i could really push corners and the car felt like it wasnt going to let go anytime soon and without the power of a turbo coming on its really safe, you notice the difference of the power being applied where its needed in the rear. I sold a helical about a year ago to a guy who races in the NZ targa, i cant remember what type of car he had but he said it had a V8 in it and he wanted the R200 diff with the helical head as its the best diff hes had for what he does as they are solid as all hell.

Ive got a great idea, why dont you get a Helical and bring that viscous down and as payment for swapping the heads over and doing a pro job give me the viscous :thumbs:
 
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