STI 20kg center differential - Subaru Forester Owners Forum
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post #1 of 22 (permalink) Old 12-08-2007, 10:09 AM Thread Starter
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STI 20kg center differential

I had the STI 20 kg center diff installed today. It went without a hitch and there were no shims that needed to be added. I'm just starting a thread to put feedback in from time to time. My initial impression is nothing. I can't feel any difference driving around with this one over my stocker. This includes going to the steering wheel lock to park it or any other tight slow turns. No difference at all. I'll hopefully make it to the track tomorrow and see if it helps any only I'll be on pump gas. Bear in mind this is just normal daily driving speed so I haven't tried to push it through a turn yet.

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post #2 of 22 (permalink) Old 12-08-2007, 10:17 AM
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I would love to know what that does. I am always looking to beef up the tranny. Is it the STi center diff that disconnects when the e-brake is pulled? Are you running stock XT axles?

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post #3 of 22 (permalink) Old 12-08-2007, 01:23 PM
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Sweet bro! Yeah keep us informed on what you like/dislike about it.

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post #4 of 22 (permalink) Old 12-08-2007, 05:39 PM Thread Starter
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Quote:
Originally Posted by toddlamp View Post
I would love to know what that does. I am always looking to beef up the tranny. Is it the STi center diff that disconnects when the e-brake is pulled? Are you running stock XT axles?
This is just a stiffer viscous limited slip. It's a direct swap with the stock one so no e-brake anything with this one. I'm still on stock axles in the rear and 03 WRX axles up front a required to run the PPG front diff since it has to run the stubby shafts coming out of the transmission.
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post #5 of 22 (permalink) Old 12-08-2007, 10:14 PM
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After all the doomsayers about increased understeer, I would love to here how this performs, both on the track and in fast road use....

Simon

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post #6 of 22 (permalink) Old 12-08-2007, 11:30 PM
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After all the doomsayers about increased understeer, I would love to here how this performs, both on the track and in fast road use....

Simon
I'm with you on this.

I guess it depends on each persons style of driving tho. I'd personally like to get both under and oversteer on demand as I wish. I do know most prolly wouldn't tho.

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post #7 of 22 (permalink) Old 12-09-2007, 06:30 AM Thread Starter
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I'm sure it would affect auto-x, but I don't do that kind of racing. Maybe once every year or so at the all Subaru ones. For auto-x or track days I hear the Cusco Tarmac is the way to go.
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post #8 of 22 (permalink) Old 12-09-2007, 07:38 PM Thread Starter
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First follow-up. Well at least with pump gas my 60' times are back down in the 1.7 range. I would get wheels spinning in the rear on the 1-2 shift. So my long lost traction is now back along with a new best time, but it wasn't without a price. Read the 1/4 mile thread (&1/8 mile) for times and the 2.5L section for the damage report as I know it.
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post #9 of 22 (permalink) Old 12-09-2007, 09:55 PM
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Already seen the damage report, thats sad, but thats a massive improve on the old 60' time.....

Simon

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post #10 of 22 (permalink) Old 12-09-2007, 11:00 PM
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Gotta find out the culprit. You obviously have a great improvement stated above. 1.7 is surly nice and can for sure get better with your new diff I think.

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post #11 of 22 (permalink) Old 12-10-2007, 06:05 AM
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Hmm...what were you running for 60' times w/out the 20kg? I was able to run a 1.8 w/out too much effort on a basically bone stock car +VF39 and DP. And that's bone stock on bald Geosquelers.
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post #12 of 22 (permalink) Old 12-10-2007, 06:20 AM
 
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When you've got a lot of power, 60' times are way harder to get low.

A friend of mine had a 1.58 60' in his old DSM. It only had a 20g, but it also had a spooled cener diff (locked, welded, whatever you want to call it). Launching that car was like getting rear-ended by a trash truck.

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post #13 of 22 (permalink) Old 12-10-2007, 08:27 AM
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will 60ft times get slower as you get more power sometimes though?

I nailed consistant 1.8s with several 1.80andchange runs. It seemed harder to hit 1.8s last time I went down there, and I was making a good 20+whp more.

Also, am I correct in assuming that doing a diff like this will add a lot more stress to the tranny?
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post #14 of 22 (permalink) Old 12-10-2007, 08:39 AM
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I can agree with that for the most part. Riding the edge between max traction and wheel spin gets a little hairier with more power. Also with bigger turbo the swing between bog and boost in larger.

Now, feeding too much power in early on a stock clutch and discovering that your car has a CVT...priceless (it actually equated to a pretty poor 60' time).
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post #15 of 22 (permalink) Old 12-10-2007, 10:17 AM
 
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When you add more power it can increase 60' times. Less low-RPM power, slower spool, less power off the line can all cause some bogging off the line.

Lots of wheel spin can be controlled with better modulation of the clutch, or lower RPM launching. You've gotta play with it a little.

Using the 20kg won't really add stress to the tranny. It'll remove stress from the pinion shaft because the stock center diff will stop unloading.

If you are JUST drag racing, I'd weld up the center diff. It would kind of suck for daily driving, but it would maximize traction. All 4 go up, or none at all.

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