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Old 03-28-2003, 06:27 PM   #1
Corn-Picker
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Question Will the STi driveline be less lossy?

A 227 HP WRX dynos at about 165. Would a 227 WRX with DCCD, mechanical rear LSD, and front viscous LSD dyno higher, lower, or about the same?

I'm hoping the DCCD and mechanical rear LSD are less lossy than the two viscous couplings the WRX currently has. Certainly the front viscous LSD will be more lossy than an open differential, but the benifits will easily outweigh the costs

If the DCCD could send 100% of the power to the rear (even though we know it can only do 65%) wheels, then there should be much less loss than a 50/50 split. So, maybe when cruising in the STi and not drifting around corners, the DCCD will put more power to the rear to reduce driveline losses

This could make the STi better than the WRX "from a roll" all else (power and gearing) being equal.
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Old 03-28-2003, 08:40 PM   #2
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Very good question. My unfounded guess is the overall "losses" will be about the same or less given the inherent sophistication of the STI drivetrain, even with the additional diff up front.
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Old 03-28-2003, 11:30 PM   #3
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> front viscous LSD

It is not, it is a Suretrac.

As far as losses go, certainly the planetary center diff of the DCCD one would think is less lossy than a VC.

Also, the 6MT layshaft and mainshaft are 10mm further apart than the 5MT meaning the gears are slightly larger diameter (overall) - whether that affects friction, I am not sure. Given the 6MT is a newer design I'd assume that it is no worse than the 5MT.

My vote: probably no worse, don't know how much better.

PS not in the driveline, but there are other friction "optimizations/reductions" in the STi. I saw that on the Japanese Subaru website somewhere.
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Old 03-29-2003, 08:14 AM   #4
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Quote:
Originally posted by Glenn Wallace
> front viscous LSD

It is not, it is a Suretrac.
I've been looking for more information on the differential. Looks like it's still a viscous differential, but it's a "ratcheting cone" type differential. Supposedly it's better for uneven surfaces because it transfers torque more quickly. Also it supposedly makes turning easier than a "standard" LSD.

Hopefully we do have a less lossy driveline than a standard WRX
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Old 03-29-2003, 10:05 AM   #5
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Most limited slip differentials rely on the viscocity of something (e.g. the diff fluid) --- when you typed "viscous" I assumed you meant "sealed viscous coupling".

My understanding is that the AP Suretrac is a torque biasing/sensitive differential.



edit: Having a look through some "other" documentation I have, it is definitely not sealed. It requires GL-5 for the entire front diff assy, and it appears to be open to the diff fluid.

Glenn

Last edited by ANZAC_1915; 03-29-2003 at 10:37 AM.
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Old 03-30-2003, 02:31 AM   #6
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This page shows part of a line drawing of the Suretrac diff (no text, but trust me that is the front diff):

http://www.subaru-global.com/lineup/...uspension.html
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