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Just in case anyone is wondering what's involved...we put a wrx tranny with v6 sti ra cryo treated gearset, wrx rear end, and rear axles in my 91 legacy sport sedan a few months ago.

What you need:
WRX tranny
WRX rear end
WRX **SEDAN** rear axles

A bolt to mount the starter and a helicoil.

The tranny bolts right up but the wrx uses a stud and the wrx uses a bolt for the starter so you'll need to helicoil the legacy block and run a bolt through the starter into the block. The speedo sensor and other harnesses etc. all plug right in.

The wrx rear end has different bolt spacing on the coupler to the driveshaft, so you put the coupler from the stock rear end on it, and you're all set.

The wrx rear axles fit up without issue. Just make sure you put the right axle on the right side (they are different lengths).

That's really about it. Easy as pie. We got wrx wagon axles without knowing it (which are too short for a sedan) and ended up running the long wagon axle as the short sedan axle, and bought a sedan long axle for the other side.

The difference in handling with the rear LSD and a center diff that isn't shot from 10 years of abuse is staggering. The car used to flip from under to oversteer and back while appliying constant throttle which was disconcerting to say the least. Now it's predictable and traction is, of course, much improved.

All we have in terms of power is turboback exhaust and boost contol so far, but at 12psi it eats stock WRX's for breakfast. If anyone has any questions, let me kow. Custom front mount IC coming soon!

-Mike

Wow. Sounds pretty fun! Is this a 91 SS with the rear LSD anyway?

91legacy_sleeper wrote:Wow. Sounds pretty fun! Is this a 91 SS with the rear LSD anyway?

It is a 91 and it did not come with a factory LSD. Neither did my friend's 91...we checked. I'm not sure which cars got them and which didn't.

-Mike

wow, i've been hoping do a similar drivetrain swap soon... did you upgrade the center diff to a 20kg?

it's good to know the lack of attitude control in the car is due to the aging drivetrain and not the driver

NuwanD wrote:wow, i've been hoping do a similar drivetrain swap soon... did you upgrade the center diff to a 20kg?

it's good to know the lack of attitude control in the car is due to the aging drivetrain and not the driver

There was a 20kg center in the car previously, but I'm running a stock wrx center and front diff at the moment. This car rotates with left foot braking as it is. At the moment my only planned adjustment is to imrove turn in. I'll be taking care of that by putting the stock front sway bar back on, or with alignment adjustments. When you snap it side to side it comes right around, but that isn't always the fastest way through a corner and I'd like the option of getting the car to turn in without flicking it.

The car was a bit frightening at times before this swap, to be honest. Power shifted from wheel to wheel in an upredictable fashion creating all sorts of undesirable behavior.

Also, with the 20kg center and stock rear diff the car did 1 wheel burnouts when you launched it. The driver side rear tire was the only one getting power.

-Mike

Innovative Tuning wrote:I'm not sure which cars got them and which didn't.

They were an option in 1991 only, I think that's the final consensus around here...

Cool stuff!

Was this a 5mt or 4eat originally?

Do you want to unload that center diff?

I wonder how the car would act with a rear LSD, and a 20KG center diff?

Hmmm, on-throttle over-steer much?

If its anything like the rally prepped 98 RS with a 20kg centre diff I've dealt with, it'll have a terrible turning radius. But in the right situations, the rear end does have a habit of hooking up quite well

subyluvr2212 wrote:

Innovative Tuning wrote:I'm not sure which cars got them and which didn't.

They were an option in 1991 only, I think that's the final consensus around here...

Cool stuff!

Gotcha. I guess the original owners of both our cars weren't performance minded. That's probably why they've held up so well. My other 2 legacy SS's are 92 and 93 so I'm out of luck on the factory LSD.

THAWA wrote:Was this a 5mt or 4eat originally?

As far as I know it's always been a 5MT.

BAC5.2 wrote:Do you want to unload that center diff?

Sure I'll sell it. I'm not 100% sure it's in there as I'm taking the previous owner's word for it. I haven't taken that tranny apart because it's in good shape. The previous owners were completely honest about everything else on the car so I have no reason to doubt it, but I haven't laid eyes on it myself. Let me know what you'd give me for it and I'll consider taking the tranny apart to find out what's really in there.

-Mike

BAC5.2 wrote:I wonder how the car would act with a rear LSD, and a 20KG center diff?

Hmmm, on-throttle over-steer much?

Rear LSD increases understeer. Front LSD increases oversteer.

Brat4by4 wrote:

BAC5.2 wrote:I wonder how the car would act with a rear LSD, and a 20KG center diff?

Hmmm, on-throttle over-steer much?

Rear LSD increases understeer. Front LSD increases oversteer.

Is this under power, or in general?

I would think under power, rear LSD would increase oversteer. If not, can you clarify why it increases understeer?

Ya, my understanding is that rear LSD increases oversteer not understeer.

It increases traction to the rear, there is less wheelspin. More traction in the rear means less oversteer.

Its that same argument from before, what it does ideally and what it does in differing conditions. And I do believe that applies to when it is under power, not sure what it does when deccellerating, are they two way or one way LSD's?

1 way, 1.5 way, and 2 way LSD's are for clutch type units only, IIRC. Vicious LSD's are, essentially, 2-way LSD's.

I don't really think it's true though, that rear LSD's induce understeer. I've never been going all out, when an inside rear tire will start to spin before the car will be sliding already. I've yet to have that lack of traction save me from oversteering. Once the car is already sliding, the tires are already in a lack of traction.

Get on the gas, and both rear tires spin together, that's all the less motivation for power to be transmitted to just one of them and helping to regain grip. Ask a muscle car guy. What's easier to spin around, a car with some form of LSD or posi, or a car with an open diff?

Conversely, the only type of front LSD that reduces understeer is a Torsen style unit. A vicious or clutch type would increase understeer under power.

In a straight line, the rear LSD increases rear traction. That's about the only time though. All bets are off when the rears are spinning already.

BAC covered it pretty thoroughly. In my experience, adding a rear LSD increases throttle on oversteer.

Adding a front LSD may increase understeer, but oftentimes it helps you drive through a corner rather than having to slide through it, so while there is less oversteer, rotation is still being achieved.

-Mike

Oh, Mike, Did the WRX case bolt up to the EJ22T just fine?

The SS tranny has 4 bolts, and doesn't the WRX tranny have 6?

Not to answer for Mike, but yeah the new engine/tranny mounting has 6 bolts rather then 4 on the older ones. Where the older ones have the two dowels on the side....That's where the newer ones have the two extra bolts. So yeah they'll bolt up just fine. Only mod you need to do is adding the starter bolt.

Sweet, so the studs replace the bolts, but all 6 hold it down. Perfect.

I'll probably be doing the WRX tranny swap soon... Someone needs my Turbo tranny, so I get to upgrade

No RA gears tho

Yup you got it. We just put a helicoil in the block and used a bolt for the starter. The hole was already the perfect size, so we didn't have to drill it out.

-Mike

Over or understeer with a rear LSD? Well, both, it depends…

On loose surfaces or with enough power to spin the wheels on pavement it will add oversteer due to the loss of traction. But up until that point both wheels will try and turn the same speed, i.e. a straight line. This understeer effect is very pronounced in my ’87 RX, (which lacks the power to easily spin the wheels on pavement), I have to be quite careful on maneuvers like entering traffic from a driveway, If you don’t anticipate the car squaring up when the boost hits you can end up on the sidewalk across the street (of course weight transfer is involved here as well). In a well sorted (and powered) AWD car the rear LDS adds great control, you can use the throttle to choose when and how much oversteer to use.

BTW, Good work on the tranny swap, I wish I could afford it.

Gary

Legacy777 wrote:Not to answer for Mike, but yeah the new engine/tranny mounting has 6 bolts rather then 4 on the older ones. Where the older ones have the two dowels on the side....That's where the newer ones have the two extra bolts. So yeah they'll bolt up just fine. Only mod you need to do is adding the starter bolt.

erm not really. There's 6 bolts, 2 studs, and 2 nuts on the new engines. Whereas the old engines have 2 bolts, 2 studs, and 2 nuts.

Does the engine have the oil/water heatexchanger?

Mike - Why not just use a bolt that fits in the block already? Or what about using the Legacy Turbo starter?

Does that make sense?

Oh, and did you find any info about my PM?

For anyone wondering if mixing and matching engines/trannys, 10 points (6 bolts, 2 studs, 2 nuts) vs 6 points (2 bolts, 2 studs, 2 nuts), is a bad idea. Subaru actually did this themselves. I believe 99 foresters have a 6 point trans and a 10 point engine. Dunno what else though. Maybe imprezas and legacys aswell. Probably in the 98-00 range.