FT4WD vs AWD?

[Phizinza]

In other words Viscous vs Open center diff...

I really don't know where to put this, but because I'm going to have a FT4WD diff locker box in my car I think I will put it here.

 

I am just interested in how the open center diff compares to the viscous unit in the later models on the road (pavement and dirt.) I know off the road with the diff locked it should be better then the viscous. That's why I'm getting one. But I'm just interested with onroad driving.

 

Cheers,

[idosubaru]

i'm not sure what you're asking.

[Phizinza]

Umm.. Basicly I just want to know how much better on road handeling is with a viscous center diff vs the open center diff.

 

I know that not many poeple have viscous center diffs in there EA series cars, but maybe the ones that have might be able to answer my question?

[robm]

I have never driven a viscous centre diff, but I much prefer the open diff to a locked one for driving on slippery roads. Locked diff for deep snow, and open diff for thin snow and ice. The locked diff on tight, slippery turns can make the car very tail happy. This won't help you at all in Australia!

 

One objection to the viscous diff is they seem quite fragile. Tires of slightly different diameters, handbrake turns etc. are all supposed to kill the diff in short order. I never managed to damage the centre diff in my AWD Corolla, and it went thousands of km with different tires front and back and side to side, and handbrake turns on the icy street to line it up to turn into the driveway were the order of the day.

 

If I could find a FT4WD with as few km as the rest of my wagon, I would think very seriously about installing it.

[nipper]

Ive driven them both, and i prefer the AWD for a great handling all around car (including on dry pavement) but i mss mr D/R.

 

 

nipper

[Phizinza]

I gather AWD is better because that's what they all use now. But I was wondering how much better. That's all.

[nipper]

Ideally, the perfectlly balanced car treats all four wheels equally. It also has a 50/50 weight balance, and the center of gravity is low and as close to the center of the car as possible.

AWD allows for all 4 wheels to be treated equally. If you really want to know the differnce, find a buddy with a late 90's AQD subaru. Take it out for a drive, then place the FWD in the holder under the hood and dirve it again (including hard acceleration from a dead stop in both a straight line and while turning). You will then see the differnce.

 

nipper

[jeffast]

from what i've read the viscous center is like having 24/7 diff lock that you can drive on pavement with, this is just what i have read no personial experance here

[nipper]

The viscous coupling is differnt. Its AWD but its not. As long as all 4 wheels are moving at the same speed, the power goes to the front in a subaru. The moment the axles turn at differnt speeds power starts getting distrubuted to the rear.

 

I posted an explination here on how the subaru manual tranny AWD works (that one has the viscous coupling). i think it was in the off topic ill try to find it.

 

 

nipper

[nipper]

http://www.autozine.org/technical_sc...ech_index.html

 

nipper

[jeffast]

linky no good

[carfreak85]

As long as all 4 wheels are moving at the same speed, the power goes to the front in a subaru. The moment the axles turn at differnt speeds power starts getting distrubuted to the rear.

 

That sounds like you are describing the torque split on the auto trannys. A viscous diff in a 5 speed box is simply a limited slip device, it doesn't alter the distribution of torque (in its most basic forms, ie viscous). Rather the center differential in a subaru will try to keep one output from out accelerating the other, front to rear in this case.

 

The only comparison I can give is between my 84 wagon with an EA82 d/r tranny and the WRX I auto x. With the wagon in 4wd, the car is a bit more difficult to turn in because the system starts binding. The viscous diff in the WRX allows a slight differential in speeds of the two ends of the car, making it a little easier to turn in.

 

An open center diff would have the least effect on the handling of the car, and would be adequet for the modest output of an EA82, but in a WRX or RS, you need to harness the traction a little better.

[casioqv]

I have never driven a viscous centre diff, but I much prefer the open diff to a locked one for driving on slippery roads. Locked diff for deep snow, and open diff for thin snow and ice. The locked diff on tight, slippery turns can make the car very tail happy. This won't help you at all in Australia!

 

I don't think Subaru ever had an open center diff, did they? I think the choices are locked, viscous, or electronically clutched. A truly open differential would be worse than 2WD, if any one wheel lost traction in the front or rear, the car wouldn't move at all. I prefer the old locking diff, because the car doesn't have to slip at all before the end with the best traction drives the car forward, and you can disengage it for better fuel economy. Sideways is the only safe way to drive on a sheet of ice, and it works great.

[Phizinza]

I don't think Subaru ever had an open center diff, did they?

 

I prefer the old locking diff

This is what I am talking about, the FT4WD EA82 trans with the center locking diff (which is open when not locked.) Or are you refering to the PT4WD box where it is 2WD or 4WD and has no center diff?

[Numbchux]

a viscous center diff on a subaru 5-speed works the same as a viscous rear diff. even torque split without load, but some speed difference is possible. the auto is a whole different animal...

 

in this thread about the RX trans, I wrote:

"I just spent 4 days with the MNSubaru at the annual Ice Race event. and quickly found out that the locked center really wasn't any different than the viscous center in the EJ cars, except you don't need to unlock them when you get out on the street. AND, you have some traction control on the street. if you try to accelerate hard out of a corner on the street (center diff needs to be unlocked) you'll get unlimited wheelspin on the inside front wheel, and no traction.

 

and with the EJ22 ... , the extra torque means it's faster to drive in hi-range, and shift less frequently

 

also, don't let the 3.7 axle ratio fool you, the gears are much shorter, and you'll be running much higher rpm's on the freeway."

 

 

also, I went wheeling with Austin about a year and a half ago, and he got high-centered with both front wheels off the ground. and the center LSD was strong enough to dig a hole under one of the rear wheels with the front wheels freewheeling...

 

 

IMHO, the RX tranny is pointless unless a front LSD, taller 2-5 gears, and lower lo range are added, or it's mated to the engine for which it was designed...

[nipper]

http://www.ultimatesubaru.org/forum/showthread.php?t=69983

 

 

or

 

http://www.autozine.org/technical_school/traction/tech_traction_4wd_2.htm#VC-differential

 

 

attack it this way

 

 

nipper

[soobscript]

FT4WD == AWD

Same function, different names.

 

The FT4WD center diff is normally open, but can be locked with the switch for a 50/50 front-rear split (aka 4WD).

The AWD box has a viscous-type limited-slip center differential, aka LSD.

(this is how i understand it, i haven't actively researched, i could be wrong, i also don't know which AWD boxes have the viscous center)

 

The newer AWD is better on street than the open-centered FT4WD, but the locked FT4WD is better offroad.

 

Is it possible to put a viscous center into the FT4WD? That would make it LSD by default and manually lockable (plus dual range)

[Numbchux]

Is it possible to put a viscous center into the FT4WD? That would make it LSD by default and manually lockable (plus dual range)

 

that's my project for the spring. I've got a guy that used to be big into the older subarus, that thinks a mazda 323 GTX viscous locking center diff could be put into an RX trans....

 

but you could put an ej viscous non-locking center in one, as long as you transfer the pinion gear aswell.

 

one of these days, I'm going to get some pictures of the fully disassembled legacy 4.111 AWD 5MT trans that I have on my workbench in the basement. that should help...

[Phizinza]

There is no easy way to get the locker and viscous in one.. They are completely different units. I can get pics and show you if you want.

[casioqv]

This is what I am talking about, the FT4WD EA82 trans with the center locking diff (which is open when not locked.) Or are you refering to the PT4WD box where it is 2WD or 4WD and has no center diff?

 

I was refering to the part time 4WD. A truly open differential, would be like the newer mercedes 4matic system that is only useful when coupled with a traction control system that applies the brakes on a wheel when it loses traction. It's not nearly as good as real 4WD, especially if say you had chains on all 4 wheels, and one fell off. That wheel would have to ride the brakes so hard to keep the car moving, the brake fluid would boil and you'd lose your ability to stop or go.

[Phizinza]

We'll I'm having the lockable open center diff and a EJ22. But my question was asked just out of interest. I just was interested to know how they compared. And I guess the only answer was "the viscous is better" which is just stating the obvious to me.

 

Oh well, I guess I'll just have to see how my FT4WD works and be happy with that.

[Numbchux]

It's a good trans, for sure. but it's not perfect.

 

every morning I pull into the school parking lot and lean into the throttle, and spin my inside front tire......I hate to think what it'll be like on an AutoX course. I'll just have to get some real sticky tires, I guess.

[Phizinza]

I wonder how much the locker can handle? I've driven a PT4WD box on the road in 4WD a fair bit and it was still ok, no difference noticed.