Differentiating Differences in Differentials

[cyniclaus]

BLUF: Has anyone driven both a LTD and a specB and can attest to the benefit of having the TORSEN rear diff versus the viscous coupling in the LTD?

 

Also, what are experiences of driving with VDC vs without? I assume the VDC was added to avoid the typical problems that TORSEN diffs have when only one wheel can bite. Does this add to/detract from the driving experience? Can the VDC be turned off like in the STi?

 

Finally, could you add full DCCD and front TORSEN to the LGT? Would the STi stuff bolt on? Would it be worthwhile? Please no smart remark telling me to buy an STi...I wouldn't be caught dead driving on public roads in anything that ostentatious (especially the new one)

 

informative article on Subaru performance differentials:

 

http://www.driveperformance.subaru.com/version5_1/blueprint.asp

 

Regarding my LTD vs SpecB buying decision: at first I was leaning towards a 2006/7 LTD because 1. it is lighter; 2. I don't need alcanthra that not only seems "boy racer", but I figure will get dirty fast; 3. I would prefer aftermarket NAV.

 

But now I am leaning towards a 2007/8 specB because of the 6-speed which is supposedly much better, and because of the differential which in theory is much quicker in torque transfer. I am assuming that if the TORSEN is really that much better, it is cheaper to buy the specB than buy the LTD and find the diff sucks and buy an aftermarket diff.

[Long Island Legacy]

I think the VLSD in the GT is not bad. I have never driven a Spec b. but i do not find the Traction control Necessary. The benefit of having the TORSEN is the R180 rear end which is a hughe plus in my opinion.

 

As far as dccd i dont think ayone has done that on here to a spec b. some guys have simply upgraded to a sti limited slip front diff. I prefer the longer gearing on the Ltd but thats just my opinion.

[f1anatic]

The main advantage that I see is the stability control. You do not need traction control on our cars. Also the 6 speed tranny is a much stronger unit.

 

Yes people have added STI or Cusco LSD front diffs. I am considering one myself. The Torsen diff. is a much better unit, but again, even with a Spec B, you will not have a front LSD. Maybe you need an STI afterall.

[cyniclaus]

The Torsen diff. is a much better unit

 

So the story goes, but have you driven both versions at the limit or do you just know this anectdotally like everyone else?

 

Maybe you need an STI afterall.

 

Yeah, a Legacy STI

 

I was at the store today and a guy pulled into the parking lot in one of the blue STIs with the gold rims, exhaust rumbliing menacingly. There was not a single person who did not turn their head and stare while he parked his car. I don't need that kind of attention.

[Albatross]

I have driven both the Spec B and LGT 5 spd, unmodded 2008s, in wet and dry. I couldn't tell the difference, and neither will 99.99% of drivers with regular day-to-day use. Autocrossing MAY show up some significant differences. However, you wont break traction in a straight line or on serious twisty bits with the AWD, so I can't see how the TORSEN diff is going to be a major advantage.

I brought this point up in an earlier post, and a contributor said the VLSD might allow as much a a 3/4 slip between rear wheels. I don't see how this is going to be a major problem.

I tried the Spec B with and without the VDC, and I felt it tended to slow it down a tiny little bit, and this is exactly what it does according to SoA, i.e. applies the brakes and reduces engine power [yikes]. I just don't believe the turboed 2.5 makes enough grunt to warrant this kind of intervention with a car driven by anyone with any driver skills. I believe it's just another pointless and expensive gizmo.

 

Cheers, Albatross.

[whitetiger]

the only place where the torsen benefits can be felt over the visous unit in competitive driving. both willtranfer power but the torsen will do it actively as opposed to wating untill there is slip berfore there is slip limiting. one of the things that really hurts benefits of the torsen rear on a spec b is the lack of a front LSD and the crappy viscous center diff. Powere is lost too easily out of the open front diff in our cars and the center diff has a hard time keeping power to the rear when one of our front wheel is in a zero traction situation. This is why i maintain that if the LGT/spec b came with a front limited slip diff, it would be totally different/better car. IMO its the Limited slip front diff and DCCD center diff in the Sti that makes the STI the superior car to the LGT in terms of performance.

 

the bottom line is the torsen is the better diff to have, but the difference can not be easily felt on the street.

[Guest]

Speaking of diffs - I am doing SpecB 6-speed swap. I had my heart set on STI box with front LSD and DCCD, but came across great deal for SpecB tranny that I could not pass up on. Tall 5th and 6th gear ratios are a plus.

 

The gearbox comes with stock SpecB R180 Torsen. I also have the clutch type R180 out of 06 STI that I bought a while ago in anticipation of the swap. Now the dillema is which one to install. I understand clutch type diff is more aggressive and works even when one wheel has no traction (in the air or on ice), in which conditions Torsen behaves like an open diff. On the other hand Torsen is said to be more forgiving and predictable.

 

I guess for street/track Torsen might be a better choice, while clutch might be better for rally/winter.

[Long Island Legacy]

All very good Info here.

 

+1 on the Legacy with a front diff. From my limited competitive use of my car (i.e 2 Auto-x's) i have noticed a significant amount of front wheel spin coming out of a corner in 1st full throttle which was a limitng factor only noticable to me under these conditons.

 

I would storngly considor the front diff upgrade in the future.

[whitetiger]

Again, it really all depends if you want to keep the open front diff or not. Torsens are a better DD diff if you have one in the front. In teh rare case were one of the rear wheels is off the ground, a helical/torsen front diff will help move the car forward even if one of the rear wheels spins. Also, clutch type rear diffs tend to induce understeer in tighter cornering. Torsen/helicals diffs dont do that because they engage smoothly and only when it senses traction loss. I think helical/torsen diffs are the best for a DD car. you get smooth engagement and no need to keep up with additives in the trans or rear diff for the clutches in other diffs.

[Guest]

Yeah, the clutch diff inducing understeer is the part that I don't like. From what I read on miata forums, the consensus is - clutch for track, torsen for autox/DD. It cost me quite a bit of work to mostly get rid of understeer on my car - it's nice neutral with a hint of oversteer now - I can toss the back around in autox quite easily now () so I don't want to bring any back.

 

OTOH, AFAIK front LSD adds understeer, too.

[whitetiger]

not the helical/torsen types. thats why the sti comes with a helical/suretrak front diff. clutch types lock under accel and braking depending on the one you get. a front torsen will only transfer power to the outside wheel when i sees that the inside wheel will spin the power away. otherwise it acts like a open diff whn under braking or cruise. this does not make any understeer. a helical/torsen diff is the only thing to put up front for a DD/autox car. no understeer sacrifice.

[Guest]

Hmmm, you're right, makes sense. Maybe I should put a front lsd in the tranny before I install it....

[cyniclaus]

unclemat, what is so much better about the 6-spd that would warrant the expense of doing a swap? Wouldn't it be more cost effective to just upgrade the 5-spd?

 

The front torsen does sound like a good idea; anyone know if they sell aftermarket ones for the LTD?

 

I don't think i can justify buying the specB only for the rear diff; I really dislike the factory NAV and the garish two-tone seats. I think the only way I'd spring for a specB is if someone can convince me that the 6-speed is really that much better and/or that it is much better suited to aftermarket suspension mods like adding a front torsen diff. Regardless of the model i buy, I plan to get ultralight wheels with fat rubber and coilovers, so the SpecB rims and the Bilsteins are no attraction either.

 

I arrive in Washington DC on 1 Nov, and I would like to buy my Legacy immediately (I've got the cash ready). But if I can't find a decent one or am still undecided between LTD and specB, I will buy a "hooptie" initially while I wait. A late-'90s Outback or WRX Wagon would be a nice hooptie

[whitetiger]

unclemat, what is so much better about the 6-spd that would warrant the expense of doing a swap? Wouldn't it be more cost effective to just upgrade the 5-spd?

 

It really all depends on how cheap you can get parts. But yes, if you have to pay book on everything, it is cheaper to just upgrade the 5spd.

 

The front torsen does sound like a good idea; anyone know if they sell aftermarket ones for the LTD?

 

yes there are several diffs that fit or cars. our 5spd box is nearly the same as the wrx/imprezza 5spd box and any diff that fits for a wrx, will fit for us. the run about $1000-$1500 for the unit and install is around $600-$900 depending on where you go.

check out the dif at the bottom of the page- http://www.rallispec.com/prod_diff.htm

 

I don't think i can justify buying the specB only for the rear diff; I really dislike the factory NAV and the garish two-tone seats. I think the only way I'd spring for a specB is if someone can convince me that the 6-speed is really that much better and/or that it is much better suited to aftermarket suspension mods like adding a front torsen diff. Regardless of the model i buy, I plan to get ultralight wheels with fat rubber and coilovers, so the SpecB rims and the Bilsteins are no attraction either.

 

so, better you get the GT then. save some $$$ and use it to buy the upgrade you want. A gt with a front LSD, coilovers and 8+" wide lightweight rims will be better than a spec b any day in terms of performance

 

 

 

I arrive in Washington DC on 1 Nov, and I would like to buy my Legacy immediately (I've got the cash ready). But if I can't find a decent one or am still undecided between LTD and specB, I will buy a "hooptie" initially while I wait. A late-'90s Outback or WRX Wagon would be a nice hooptie

[Long Island Legacy]

unclemat, what is so much better about the 6-spd that would warrant the expense of doing a swap? Wouldn't it be more cost effective to just upgrade the 5-spd?

 

The front torsen does sound like a good idea; anyone know if they sell aftermarket ones for the LTD?

 

I don't think i can justify buying the specB only for the rear diff; I really dislike the factory NAV and the garish two-tone seats. I think the only way I'd spring for a specB is if someone can convince me that the 6-speed is really that much better and/or that it is much better suited to aftermarket suspension mods like adding a front torsen diff. Regardless of the model i buy, I plan to get ultralight wheels with fat rubber and coilovers, so the SpecB rims and the Bilsteins are no attraction either.

 

I arrive in Washington DC on 1 Nov, and I would like to buy my Legacy immediately (I've got the cash ready). But if I can't find a decent one or am still undecided between LTD and specB, I will buy a "hooptie" initially while I wait. A late-'90s Outback or WRX Wagon would be a nice hooptie

 

Can we see this sierra cosworth you have in your profile. LOL

[cyniclaus]

yes there are several diffs that fit or cars. our 5spd box is nearly the same as the wrx/imprezza 5spd box and any diff that fits for a wrx, will fit for us. the run about $1000-$1500 for the unit and install is around $600-$900 depending on where you go.

check out the dif at the bottom of the page- http://www.rallispec.com/prod_diff.htm

 

Thanks for the info. Could be funny to get that front diff for the LTD and you'd have a torsen in the front and a viscous coupling in the rear

 

so, better you get the GT then. save some $$$ and use it to buy the upgrade you want. A gt with a front LSD, coilovers and 8+" wide lightweight rims will be better than a spec b any day in terms of performance

 

That's what I'm thinking. If I got a specB I would want the 08 for the grey seats. That's a huge price difference between an 06 or 07 LTD and an 08 specB...money I could use to do the aforementioned upgrades

[cyniclaus]

Can we see this sierra cosworth you have in your profile. LOL

 

Yeah, I hate to lose her, but she's completely unregisterable in the USA, unless I import her as a pure track car (which I'm half tempted to do considering all the money I've :cough: "invested"). For those who don't know what this car is, it's a WRC super sleeper 4-door AWD sedan with a Cosworth engineered 2.0 Turbo. The closest we got in the States was the very limited edition Gallant VR4...but the Cossie is lighter and IMO much better looking. This is a popular tuner car in Britain. Stock crank hp was 220, but I'm up to about 350 right now at 1.6 BAR with a Garrett T35 and stock FMIC. Not bad power for an AWD car that weighs less than 3000 lbs

 

here she is:

 

http://pichostonline.com/u/081017/10e772d931.jpg

http://pichostonline.com/u/081017/5685aaf885.jpg

 

In the early '90s, Europe got all the fun turbo AWD rally cars...the Sierra and Escort Cosworth, the Opel Calibra AWD Turbo, the Celica Gtfour ST205, the Audi RS2, the Lancia Delta Integrale, etc.

[Long Island Legacy]

Wow that car would be sick here even for today's standards