Front LSD?

[2.5GT_NJ]

Has anybody tried to swap the front open diff. w/the one from the STI? Or know if somebody like Cobb has one in development?

[axis008]

Nope, at least not that I know of. But I sift through almost every post here so, not yet :). I'm sure someone later might do it. Most people here are just into minor mods, so anything extreme is rare.

[SUBE555]

I haven't heard of anyone throwing a front LSD in yet. It *might* be on my list of things to do pending how competitive I want to get with my car, but I'm more apt to wait for an STi Wagon (Impreza or Legacy) than actually have to tear down the tranny to put a different front unit in when it actually works fairly decently.

[legacyb-spec]

Read an article about the LSDs on Club Legacy no.4. The test was done on a 1990 legacy, but the results should hold true for most Subaru AWD systems. The car was test driven under these conditions: Step1: F:open diff R:viscous type (stock condition) Step2: F:open diff R:mechanical 1way Step3: F:mechanical 1way R:viscous type Step4: F:mechanical 1way R:mechanical 1way note: the mechanical 1way they used was the Cusco typeRS 1way. Results: Step1: Nice set up with no weird habits. However, the front end seems to lose traction when exiting the corner, resulting in understeer. This type of understeer was strong especially on slow turns. Time:54.322 Step2: The car came more rear end happy resulting in a FR-like driving style. However, the front end still experienced understeer depending how much throttle you gave after the apex. Time: 53.723 Step3: The car's steering became slightly heavier due to more traction in the front. Despite that, the car turns in a lot sharper than the previous steps. Even in you open the throttle at the exit, the front tires gripped and pulled the car forward. However, the way the car acts between throttle on/off is totally different, resulting in a car that requires high skill to master. Time: 52.547 Step4: When entering a corner, the car did not over nor understeer. The traction characteristics is totally different from step3. Even if you open the throttle during the turn, the car stays put. The result is a drivable neutral handling car. You can make it under or oversteer with the steering alone. Time: 51.996 They tested with only a 1way LSD, but you can use a combination with 1.5 and 2way to find the setting that fits your style.

[SUBE555]

Thanks for that input! That is rather interesting! Somewhat what I expected to see, but none-the-less, nice to see in writing. :)

[legacyb-spec]

As far as the upgrade goes, the article stated that its a choice between drivability or lap time. If you want to just upgrade it to work more like a FR, just replace the rear viscous LSD with a mechanical one. You can drive little more aggresively. However, the article also wanted people to experience the F/R mechanical LSD setup. How the front tires just pulls you even when oversteering is amazing. Although there is a huge difference in driving characteristic between throttle on or off, fast lap times are yours if you can master this habit. You also need to upgrade the clutch to handle the added traction and mechanical LSDs need to overhauled at least every 2-3years. Phew that was some article. gave me something to think about. The STI setup is viscous front and mechanical rear. Complete opposite from step3. I wonder how that setup is on the track. Any STI owners?

[outahere]

[quote name='legacyb-spec']......They tested with only a 1way LSD, but you can use a combination with 1.5 and 2way to find the setting that fits your style.[/quote] Never heard of LSDs being described as one way, two way, etc. What does it mean?

[SUBE555]

This link seems to descibe a few things, particularly the 1, 1.5 and 2-way abilities: [url=http://www.club4ag.com/faq%20and%20tech_pages/limited_slips_differential_101.htm]INFO[/url] legacyb-spec, the 2005 USDM STi's uses a Helical mechanical-type of differential up front and supposedly a clutch-type rear, while the 2004 was apparently a viscous-type unit, though I'd heard they may have just changed suppliers and the previous being a helical unit as well. I've been told by some that the difference from 04's to '05s is aparent, while others say the feel and characteristics have changed little. For my current GT, if I were to do anything, I'd probably just add a helical unit up front and leave the center and rear as viscous. That's if I were to upgrade any. That appears to be the recommended units for Subaru's to be somewhat more competitive, but you need to change everything if you want to be really competitive, then it's not a road car anymore and the Legacy is not the right car to be doing all of that to at that point then IMO.

[IwannaSportSedan]

Just curious, but what would folks recommend for the best possible street-driveable, neutral handling on accelleration, and braking combination of differentials? I have heard that Helical gear torque-sensing diffs are the best. due to their 100:0 <-> 0:100 torque-based transferring capabilities. Are there advantages to a viscous type? In an ideal world, I would love a Subaru Legacy (GT modded, or STi) that would put an Audi Quattro-driven car to shame. How do you think a car with F: 1-way C: 1.5 way R: 1-way torsen style diffs would drive? I am interested in this subject, purely on a theoretical level, and would love to learn more.

[Deer Killer]

[quote name='IwannaSportSedan'] In an ideal world, I would love a Subaru Legacy (GT modded, or STi) that would put an Audi Quattro-driven car to shame. [/quote] AFAIK quattro's have been coming with only a center LSD and EDL (brake controlled locking) to control the front and rear diffs for a while now. GT is already more advanced with two LSD's. It's good enough for the way most people will drive this car, but with so much power I've already spun a single front wheel during hard acceleration in first, many times. Beyond first gear though, it would be at far from legal speeds.

[IwannaSportSedan]

I think it would be cool to have an AWD system that is fully variable, and torque sensing, front to rear and side to side, and neutral handling on the street. It would probably inherently do very well on snow, too. Somehow, using the brakes to affect differential action, on recent Quattro systems seems overly complex, when a good LSD can do it inside the differential itself. Didn't previous longitudinal Quattro systems run two or three torsen LSDs?

[Deer Killer]

[quote name='IwannaSportSedan'] Somehow, using the brakes to affect differential action, on recent Quattro systems seems overly complex, when a good LSD can do it inside the differential itself. [/quote] It's not there because it's better it's there because it's cheaper.. it doesn't even operate above a certain speed threshold (25, 35?) Also the brakes will overheat and it will stop working if you really push it in loose conditions (snow)

[RobY]

Subaru AWD already kicks the crap out of the current line of quattros. They are brakeforce differentials which anybody can tell you its use for any performance oriented situation is POOP. The quattro is basicly 2 wheel drive, one front one rear, never more than 2 at the same time. But has the ability to pulse bilaterally . Its ony really a way to find which wheels have more traction not to add traction. Also in certain situations the Subaru Viscous Coupling Locking Differential is superior. Its not a tradtitional viscous unit. Its a viscous locking unit. The viscous locking unit dosent transfer force through a viscous fluid like a normal viscous coupling differential. A viscoous coupling locking differential consists of a normal differential that becomes locked when a viscous coupling starts slipping. It results in an immediate and static 50:50 transfer of torque. Theis has been used to GREAT effect in rally racing in the past. It has some really favorable characteristics in LOW tractive conditions since when it is engaged it acts as a locking differential. however you could probably get around the tarmac faster with a torsens. .