Open Diff vs Helical

[bnr32jason]

I haven't really seen much discussion about the lack of differential in the WRX transmission. Do most people think it won't be a problem?

I've been specifically searching for a fairly rare STi RA 5-SPD transmission that has a built in helical diff here in Japan. They were offered in small quantities on certain model STi's here. I'm actually checking one out today that will run me $450 including the matching rear diff and DCCD wiring and ECU box. I obviously won't need the DCCD stuff or the rear diff but I should be able to sell those to recoup a couple hundred bucks.

I can't imagine running an open diff on a car such as this. Are the Factory Five test cars running open differential? Or have they installed an aftermarket differential?

[RM1SepEx]

I went with a quaife, erik is using the OBX (quaife clone)

I just got mine back from the shop today! my last piece for my build! $1033 for the Quaife, $225 for the install, $250 for new carrier bearings (orig didn't feel "right") and seals...

See Erik's thread re the OBX... it is identical in operation to the Quaife helical and about 1/2 the cost. You do need to rebuild it before use tho...
I wouldn't run a 818 w/o an LSD

[philly15]

im gonna run the obx first and do the washer upgrade, i was trying to decide between running either a cusco or kaaz 1.5 way clutch type lsd but i just didnt wanna spend the cash right now when you factor in the cost of fluids having to flush it every 4-6k miles it gets expensive! plus all that clutch material going right into your gear oil sure to shorten trans life im gonna give the helical a try and if it totally sucks ill switch but for a third of the price id give it a shot any day of the week!

[Red Tag]

The 818R (and 818s) used for FFR track testing both had open diffs. A diff is a good idea, usually, but we have to see how the chassis setup is going to be. Generally, a torsion LSD will create understeer on corner exit. It seems like they already have a corner understeer issue with the cars, so a LSD may just make it worse. It is still early yet.

[bnr32jason]

The test cars were running 06 WRX running gear right? That would mean an open diff with 3.7 FD.

[RM1SepEx]

Open Diff = one tire fire :eek:

[Xusia]

And yet it STILL managed to pull 1.5 G's...

My strategy with this - as with virtually everything as it relates to the 818 - is to go with as close to stock as reasonable. Then (and only then) if there are issues I think need addressing, I'll address them. I have no interest in solving problems that don't exist!

[metalmaker12]

I have one 5spd with a used Cusco 1.5 Lsd and another one that is stock with open diff. I will probably run the open diff to get a baseline. If they have an understeer issue, it could lie in the rack. The stock racks ratio is not really a performance rack and give the wrx understeer. Even the sti have the same issue. I had to get a quick rack or quick column setup in my previous subies to get them to oversteer like I wanted. This is why the Jdm sti's handle better, the racks have way faster ratios. The 818 is a different beast and might have other reasons for understeer, I am sure they will sort it out.

[bnr32jason]

What's the steering ratio for the US WRX steering racks?

For the JDM STi models they seem to range from 2.7 turns lock to lock and even as low as 2.2 in certain models. I'm trying to source one now.

[SixStar]

We're going to be running the OS Giken in our R and our S. From my experience it's one of the best front LSD's out for the GD8 chassis.

[Wayne Presley]

Mine will have a helical diff, any of the turbo cars I feel that a limited slip should be a mandatory install.

[metalmaker12]

q-racks are 11.5:1 or 12.5:1, Usdm wrx 02-04 is 16:5:1 Usdm Wrx STI 05-07 is 15:1, a Jdm Sti is 13:1)

STi upgrade, cheap and easy
L&E Fabrication quick column, still cheap and easy but super fast ratio
Q-Rack, crazy expensive compared to the other two but most common upgrade

A lsd on the 818 might be a great upgrade, but I am going to try open and than with and see how it goes.

[Bob_n_Cincy]

q-racks are 11.5:1 or 12.5:1, Usdm wrx 02-04 is 16:5:1 Usdm Wrx STI 05-07 is 15:1, a Jdm Sti is 13:1)

A lsd on the 818 might be a great upgrade, but I am going to try open and than with and see how it goes.

I agree that a LSD is a good thing on most cars. When a car leans in a corner the inside wheel has reduce traction allowing it to spin easy.
The 818 has a low CG so not as much body roll. So LSD is not as critical. Is my physics correct here?
Bob

[Wayne Presley]

I agree that a LSD is a good thing on most cars. When a car leans in a corner the inside wheel has reduce traction allowing it to spin easy.
The 818 has a low CG so not as much body roll. So LSD is not as critical. Is my physics correct here?
Bob


The NA cars lower HP you can get away with an open diff but the turbo cars have more than enough HP to spin even a sticky single tire on corner exit.

[wleehendrick]

The 818 has a low CG so not as much body roll. So LSD is not as critical. Is my physics correct here?

Neglecting body roll, the inside drive wheel is still following a shorter arc, so there's more mechanical advantage on it, which is why it will loose traction under acceleration first.

[wleehendrick]

I'll add that I won't be installing a LSD initially, partly to keep the build within a reasonable budget, also due to the fact that my donor is an 06 with fairly low miles and a solid clutch. I'm not planning to pull the trannie off at all. At some point in the future, I'll probably add an LSD when it's time to replace/upgrade the clucth, and perhaps flywheel.

I actually think that for those people not used to RWD and/or mid-engined vehicle dynamics with no electronic nannies, would be better to not have a LSD. The LSD makes the rear want to come around by putting more torque to that outside rear wheel, whereas an open diff, which will just spin the inside drive wheel, is more tolerant of ham-fisted throttle application.

[guitaraholic]

The 818R (and 818s) used for FFR track testing both had open diffs. A diff is a good idea, usually, but we have to see how the chassis setup is going to be. Generally, a torsion LSD will create understeer on corner exit. It seems like they already have a corner understeer issue with the cars, so a LSD may just make it worse. It is still early yet.

I am not 100% on this,,but won't a clutch type and even a VLSD create a more understeer prone car, while a torsion would help with oversteer. Let me explain. With a clutch/plate type LSD, the wheels are locked turning the same speed. Torque is split evenly so each wheel is putting 50% of the power down. The would tend to make the car want to go straight (understeer). Not saying you can't put your foot down and create some throttle oversteer.

With a torsion the torque is split (though not evenly) between the two wheels. The one with the most grip (usually the outside tire), has the most torque applied. This in itself would lend to a more oversteer prone handling characteristic. The outside wheel is actually trying to push the car around.

There are some advantages and disadvantages to both.

Clutch:

pros:
- You can dial in how quickly it engages and releases
- With a two way you can dial in both accell and decel lockup settings
- Good for drag racing because of the even 50% of power to the wheels
- Does not have to have both wheel in contact with the ground to work
cons:
- Sometimes noisier
- You have to replace the clutches (it does wear out)

Helical

pros:
- Better for road courses/autocross because of oversteer handling characteristics
- Drives like stock, most of the time you don't even know it's there because it acts like an open and smooth engagement
- It will probably outlast your car

cons:
- If you lose 100% traction on one wheel (ie wheel liftoff or ice) it will act like an open
- you are pretty much stuck with the torsion bias you have (1:3), (1:5),, and so forth,, though some you can tune

I'm actually getting a wavetech put in my SL-C, It's a torsion but has a special feature that allows traction when one wheel looses 100% of grip, and you can actually tune it (not sure how yet)

[Silvertop]

I've been considering a Quaife LSD for my 818S build, although my NA application makes this less critical. But here's my question: All the websites I have checked seem to offer only Quaife units for Impreza calendar years 1993-2000. Aren't they available for newer 5MT applications?

[RM1SepEx]

yes... http://www.sparktecmotorsports.com/qua-qdh1y.html?utm_source=googlepepla&utm_medium=adwords&id=20861070197&utm_content=pla

http://www.autotech.com/mm5/merchant.mvc?Screen=PROD&Product_Code=93-309-150&Store_Code=stock&search=wrx+diff&offset=0&filter_cat=&PowerSearch_Begin_Only=&sort=&range_low=&range_high=

[Silvertop]

yes... http://www.sparktecmotorsports.com/qua-qdh1y.html?utm_source=googlepepla&utm_medium=adwords&id=20861070197&utm_content=pla

http://www.autotech.com/mm5/merchant.mvc?Screen=PROD&Product_Code=93-309-150&Store_Code=stock&search=wrx+diff&offset=0&filter_cat=&PowerSearch_Begin_Only=&sort=&range_low=&range_high=

Well, that was a short discussion.....:) Thanks -- just what I needed.

[longislandwrx]

That's a good price from Autotech... ever buy anything there?

As stated the QDH1Y should fit... I don't know why no one ever updates the application list IIRC they fit all 5mts 93 and up.

Guaranteed Fitments:

Impreza and Legacy AWD Front, including WRX USA 5-speed (not STi) - (2002-2005)

I've also seen

Applications:

Subaru Legacy incl. Outback 1993+ FRONT diff
Subaru Impreza 1993+ FRONT diff
Subaru WRX 2002-2005 (not Sti) FRONT diff

[GUNS]

yes... http://www.sparktecmotorsports.com/qua-qdh1y.html?utm_source=googlepepla&utm_medium=adwords&id=20861070197&utm_content=pla

http://www.autotech.com/mm5/merchant.mvc?Screen=PROD&Product_Code=93-309-150&Store_Code=stock&search=wrx+diff&offset=0&filter_cat=&PowerSearch_Begin_Only=&sort=&range_low=&range_high=

Has anybody bought from autotech before? I'm getting ready to buy one and that's the cheapest I've seen them.

[longislandwrx]

I think they look legit. Grammar is good on the website and 2000+ Facebook likes. Seems safe.

I might change my diff plans for that price.

[RM1SepEx]

I bought mine from Autotech... And I paid a bit more too!
And it is installed now, by Subaru dealer/shop fitment is correct

[longislandwrx]

What did they charge you with the trans already out of the car?

[RM1SepEx]

$225 labor, installed all new seals, new carrier bearings too and removed the center diff and output shaft, checked everything else

[longislandwrx]

That sounds like a great deal. thanks for the info!

[BrandonDrums]

Wow, 250 to install a diff with the trans out of the car! I think I just lost my excuse for not doing mine right away.

[Silvertop]

Is autotech about to experience a run on LSD's, I wonder? :p

[philly15]

Out of curiosity how does this translate to the 06-07 5 speed? Anyone know?

[RM1SepEx]

As far as I know it is the same PN

[GUNS]

Bought mine :).

[philly15]

As far as I know it is the same PN

ok cool just thought id ask since manufacturers like kaaz and cusco split their lsd's up by 02-05 and 06-07 but obx says 02-06 didnt know if the different axles of the 06-07 would pose an issue?

[RM1SepEx]

Don't forget Erik T did up an excellent write up on upgrading the OBX (Quaife Clone) It comes with crappy springs and bolts. You can save a few hundred $ by using the OBX

[longislandwrx]

http://thefactoryfiveforum.com/showthread.php?8783-OBX-LSD-rebuild-step-by-step-pics-inside

[tmoretta]

Yes, why are the OBX limited slips so cheap? Anyone have any experience/history on the unit? Also, why do some guys say it has to be "rebuilt"?

[longislandwrx]

The link I posted explains why they need to be rebuilt. They are so cheap because they are a Chinese made forgery of the Quaife unit and therefore do not have to recoup engineering testing or development costs.

the quality control on the Quaife is better and comes with a warranty, you are paying for that as well.

[Tom Veale]

I've used Quaiffe and Torsen differentials for years. They're great. Someone mentioned that if the inside wheel lifts clear of the pavement the diff acts like it's "open" and that is only partly true. Since the left and right wheels are interlocked through Gears, one can't spin without the other being driven. The gear ratio determines how fast the inner will spin vs the outer's being driven. Yes, it spins, but there's still a portion of the torque being delivered to the outside wheel and therefore different from an open diff.

FYI - It's not uncommon in some cars to hear the revs climb while cornering hard as that inner wheel spins up, but the car is still being propelled forward. This is what leads people to believe it acts like an open diff.

[longislandwrx]

http://forums.hybridz.org/index.php/topic/57834-obx-vs-quaife-with-pixors/


quaife vs obx

[philly15]

thought id post this up for people still looking into the LSD option and what they want to go with another option other than those listed is the M Factory lsds they offer a torsen type as well as 1, 1.5, and 2 way clutch types the torsen is 685 and the clutch type 900

http://www.teammfactory.com/home

also here is the differential faq thread from NASIOC has some good info

http://forums.nasioc.com/forums/showthread.php?p=15812529

[RM1SepEx]

My Quaife was very nicely finished with their logo lasered into the side. I have pretty extensive background with precision machining and the Quaife is very well machined. It did come in an ugly plain cardboard box tho LOL

[tmoretta]

The link I posted explains why they need to be rebuilt. They are so cheap because they are a Chinese made forgery of the Quaife unit and therefore do not have to recoup engineering testing or development costs.

the quality control on the Quaife is better and comes with a warranty, you are paying for that as well.

How about the Tomioka brand helical gear type limited slip? Any experience with it? Costs about $850.

[RM1SepEx]

All I know is for about a grand you get a lifetime warranty with the Quaife, I have tons of friends that swear by them... That Tomioka looks like a quality piece in the photos

[metalmaker12]

If your going to spend the money on a subaru tranny and get the best quality and durability street or track it goes 1. Cusco, 2. Sti gruppe N 3. Quafie and all others are no were near the three. I have used all and I like the cusco the best, but the others are spot on as well.

[longislandwrx]

Autotech took the part down, bummer!

[GUNS]

Autotech took the part down, bummer!

Yup, got an e-mail saying my order wasn't processed. Any other places would good prices on these?

[bnr32jason]

If your going to spend the money on a subaru tranny and get the best quality and durability street or track it goes 1. Cusco, 2. Sti gruppe N 3. Quafie and all others are no were near the three. I have used all and I like the cusco the best, but the others are spot on as well.

Interesting, I can get the Cusco here for a decent price ($800), it's the Cusco Type RS Spec-F. One of the reasons that I want the factory LSD is because I've had pretty bad experiences with aftermarket LSD's in used-cars that I have purchased. They have functioned well, but they also are very clunky, noisy, and I just don't like the feel and sound in low speed situations like parking lots. Is this about the same as the experience with the Cusco LSD as well?

[RM1SepEx]

Perhaps they sold out!
if $ is a big concern buy an OBX and rebuild, Erik has a great tutorial on this forum. No lifetime waranty but about $500 will get you an OBX with the parts needed to "fix" its shortcomings... The Sube forums indicate that they will hold up if the springs and bolts are replaced.

[bnr32jason]

Are there any aftermarket front differentials that are quiet? Or are they all noisy?

How about the OBX? I've dealt with noisy diffs before and it's annoying. I'm not building a track car, so I want something quiet. I'd honestly rather go open diff than have a noisy diff.

[Wayne Presley]

the OBX, quaife are both quiet gear type diffs.

[bnr32jason]

Oh ok, thanks for the information. I'm still pretty new to this stuff.