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Old 09-26-2008, 02:35 PM   #76
neilschelly
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I was thinking of a tranny build this winter as well, but in trying to save money, I may put it off. That said, I've never built a tranny so it sounds like fun if I find the right one to get started with. I enjoyed building an engine last winter and had never done that, so how hard can it be? ;-)

I was also planning on new front/center diffs while I'd be in there, though now I'm starting to question the need for the center diff. If a weak viscous is close enough to open, maybe it doesn't matter. The torque distribution further back than 50:50 would be nice, but would it be worth the cost? And aren't those diffs really hard to find?

My other question was what tranny I'd get to start said project. In street prepared, I'm allowed any transmission from any '93-'01 Impreza except the RS. I think there were two different gearsets for the 1.8 and 2.2 engines and figured I'd go for the shorter gearing of the 1.8 transmissions, but I've never found any definitive listing of the gear ratios, or more specifically, I've found several definitive Subaru-published sources that have failed to agree.

Do any of the builders in this thread have enough Subaru-specific experience to know something to shed some light on which transmission options there are and if any particular 5MTs are compatible or incompatible with the various diff options we're discussing? I'm assuming they are all the same except the obvious differences in the few FWD ones out there. Perhaps it's the FWD ones that have the alternate gear ratios, which would be unfortunate I guess.
-N
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Old 09-26-2008, 02:39 PM   #77
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the EJ18's have the exact same gearing as the RS'
I've taken two of each apart...usually related to blowing them apart

I know Sean (speedyham...above) had a factory fluke EJ22 that came with 4.11's too and is still the only one I know of.

Most EJ22's or at least all were specified as 3.9 final drives while the EJ18's were 4.11 to help with their lack of power...I'm not sure of the transimssion gearing on the 3.9 transmissions however. With my experience with subaru, I'd be suprised if it were different.

The front is a standard r160 as is the rear diff. I have yet to find out if the center diffs are interchangable between phase 1 and phase 2 trannies, as my built 5-spd project (using my ver 3 RA DCCD center on a 02 wrx trans) went on hold when I got the 6-spd.
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Old 09-26-2008, 02:55 PM   #78
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Well, I wasn't referring to ring/pinion ratios, but gear ratios. I never heard of an EJ22 with 4.11 gearing before now, unless it was an automatic. Knowing that it fits means I may want to see about getting a 4.11 ratio into my eventual transmission build project to get the shortest gearing possible, but that would be a gray area between class allowances to modify diffs, but not transmission internals... hmm...

I also didn't know there was an definitive phase change for transmissions, or did they change somehow when the engines switched to Phase 2?
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Old 09-26-2008, 03:13 PM   #79
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Some personal observations on the CUSCO 35/65 center...

Keep in mind that this is an "open" diff with no limited slip action. This is why CUSCO recommends you have effective limited slips both front and rear.

This means that if you break the rears loose under power, there will be no lockup to send torque to the front and vice versa.

Between the lack of limited slip action and the static torque bias, there's a very significant difference in how the car handles. So much so, you'll have to set the chassis up quite differently AND drive differently. It's much more like driving a RWD car and the setup considerations follow suit, also.

This is my experience with roughly 212 ft/lbs of torque to the wheels. With significantly more, you'll most certainly have to treat that right pedal with respect and use a setup that optimizes rear grip. If you have a very non linear torque output (e.g. turbo lag, then "blame!"), you'll probably have a hard time controlling where the car goes.

Regardless of your torque ouput, what you won't get is that "binding" feeling where you're on the power in a turn and you can feel the drivetrain get loaded up and ultimately fight understeer, or just plow like a pig. This, I attribute to the lack of limited slip action, not necessarily the torque bias. This is why I suggested to Jay that he try a regular center diff minus the "goo", converting it to an open 50/50 center diff. This will, IMO, result is less power-on understeer (assuming you have any...), so you can get on the power earlier in the corner.

In another topic: For those of you building trannys and thinking gear ratios I highly suggest you first consider what wheel/tire combo you'll be running before you make your ratio decisions. Jay's FSP Impreza is on 13s and the DSP RSs are on 15s both of which have a significantly smaller rolling diameter than a stock Impreza.
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Old 09-26-2008, 03:20 PM   #80
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Another benefit of running something like the Cusco open 35/65 center diff would be the allowance of running a staggered tire setup. I know Nate has told me many times he thought I could benefit from such a setup, but the realities of a viscous center really just don't give that a chance. If we're talking about putting a nice front and rear diff together though with an open center, the possibilities could be quite interesting.

Now I gotta go think in a corner... I'm feeling a little un-Suby-like with thoughts of staggered tire setups in my head. Hmm...
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Old 09-26-2008, 03:53 PM   #81
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Quote:
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Now I gotta go think in a corner... I'm feeling a little un-Suby-like with thoughts of staggered tire setups in my head. Hmm...
-N
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Old 09-26-2008, 04:03 PM   #82
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Is it worse that you immediately thought to post that graphic or that you had that graphic at your disposal ready to post at a moment's notice?
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Old 09-26-2008, 04:10 PM   #83
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Quote:
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Is it worse that you immediately thought to post that graphic or that you had that graphic at your disposal ready to post at a moment's notice?
-N
Check the time stamps. It may have taken me 30 min to find it, or, I lept ahead in time to make it *look* like I didn't have it immediately available.

You choose.

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Old 09-26-2008, 04:43 PM   #84
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Neil, with the 275/25/15's, you have both the 205's and the 225's to use with tire stagger, both with the same OD as the fronts. You're viscous diff won't even notice.

Also, with an open diff and tire stagger, you can tailor your front/rear torque split with tire OD. Wrap thy brain around THAT idea!
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Old 09-26-2008, 09:04 PM   #85
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Heh, the cusco 36/65 center sounds just like an '04-'05 STi DCCD set to MANUAL and set to full rear... They should both yield a 35/65 torque split with no LSD in the center.

Problem is, in an STi, the turbo coming on makes the car decide to swap ends. The lack of anti-squat in the rear suspension makes it SO easy to do too (maybe that's why they're good at drifting when converted to RWD)... Too bad that's not the fast way around.
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Old 09-26-2008, 10:36 PM   #86
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First, English is not my first language. Sorry if some part sound strange

This is realy a nice thread. I was trying to figure what to do with my rear inside wheel all summer long.

I am running a 93 L impreza with a complete STI veriso v6 ra limited swap. So helical in the front, DCCD and rear R180 LSD.

In the past, I ran a little honda civic in rallye and solo2. Like any FWD, I had no front sway bar and big rear sway bar.

I have tried a lot of setup on my impreza and found that it react very well with a "FWD setup": No front sway bar and 22mm rear sway bar.

It was tail happy on corner entry and I tuned the exit with the DCCD. I started with the DCCD full "rear" and adjusted the DCCD more and more to the front untill it was not oversteering on corner exit.

The rear LSD started to get weekr and weeker to a point where it is not locking anymore.

So I started to convert my setup to a "rwd" setup to keep both rear whell on the ground. No rear sway bar, stock STI front sway bar, less camber in the rear and more pressure.

The car feel COMPLETLY different. Still tail happy on entry, but grip better on exit. BUT, even with more rear grip sooner, I CANT accelerate faster because of exit understeering!!

So my conclusion is that on solo2 event, inside rear wheel lift is not a problem because it BALANCE the car to avoid natural tendency to understeering.

Last edited by Sylvain b; 09-26-2008 at 10:47 PM.
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Old 09-26-2008, 10:55 PM   #87
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Quote:
Originally Posted by solo-x View Post
Neil, with the 275/25/15's, you have both the 205's and the 225's to use with tire stagger, both with the same OD as the fronts. You're viscous diff won't even notice.

Also, with an open diff and tire stagger, you can tailor your front/rear torque split with tire OD. Wrap thy brain around THAT idea!
Ah... I'd never compared the 275s to the other tires. Last time I considered a stagger was before they came out and I couldn't find any matches.
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Old 09-26-2008, 10:59 PM   #88
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It is a problem if it is still up when you get back on the throttle... The stock STi diff is weak and allows the inside rear to spin up (which makes the diff weaker). In the meantime, the outside rear gets very little power and the DCCD isn't doing a very good job of sending it more towards the front, so the car actually slows down. When the inside rear finally comes back down, WHAM! It hits the ground really hard. Hard enough to break the diff sometimes. It's happened before.

I agree, as long as it's only up on corner entry. However, I'm on the gas earlier than most, sometimes at the apex, and I can't have the wheel up there.
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Old 09-26-2008, 11:23 PM   #89
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Just one question that nobody ask before, but do you think that adding an Anti lift kit (whiteline for example) could make the problem worst?

It will help the front to be more compliant BUT will add more nosedive on corner entry!!??
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Old 09-26-2008, 11:53 PM   #90
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That's way too late, in my opinion.....especially when turbo response plays into things.
Quote:
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I agree, as long as it's only up on corner entry. However, I'm on the gas earlier than most, sometimes at the apex, and I can't have the wheel up there.
This is one reason why the front helical or TorSen LSD is such a big help. As soon as the front end takes a set into the turn, you can add power and literally feel the front diff pull the nose toward the apex. Being able to get the power down before the apex is such an advantage....the next straightaway becomes much longer!!!! With a good clutch type rear diff, the rear wheels will still provide power to the ground even if there's ony one on the ground.....at least until you overpower the clutch and it begins to spin. Even then, the difference between that force and what is possible with a vlsd or open diff is night and day.

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Old 09-27-2008, 12:47 AM   #91
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Exactly... Hence my desire for a good stiff rear diff... I don't think it will hamper turn-in because if I setup the car to actually handle like a car with 60% of its weight on the nose should, the inside rear will be in the air and can't hinder turn-in.

Now, on mine, the problem is the DCCD. I think the DCCD controller should be sensing the runaway rear wheel (since the wheel sensors is where it gets its data) and be engaging the clutch to send more to the front helical diff. But it doesn't.

Now, it took me a while to figure out that the DCCD has a kill switch. It's the same switch used to turn the brake lights on. So if you LFB and play that "hover the pedal in the void between the switch and pad engagement" game, the DCCD is totally useless because it will be open all the time the brake lights are on, whether you are actually slowing or not.
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Old 10-01-2008, 04:33 PM   #92
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Quote:
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Now, on mine, the problem is the DCCD. I think the DCCD controller should be sensing the runaway rear wheel (since the wheel sensors is where it gets its data) and be engaging the clutch to send more to the front helical diff. But it doesn't.
Not calling BS here... but how do you know it doesn't engage?

Quote:
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Now, it took me a while to figure out that the DCCD has a kill switch. It's the same switch used to turn the brake lights on. So if you LFB and play that "hover the pedal in the void between the switch and pad engagement" game, the DCCD is totally useless because it will be open all the time the brake lights are on, whether you are actually slowing or not.
You should be able to adjust your brake pedal free play so tight that you can get pad engagement before you get brake lights, without dragging. You could even shim the part of the brake pedal lever that engages the brake lights to give you more light braking room without turning on the brake lights.

-Mike
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Old 10-01-2008, 05:15 PM   #93
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So to make sure I understand...

-You want "all" the diffs engaging during ACCEL....Correct...
-You want the Front, center and Rear to engage when coming "OFF" a corner...
-You don't want engagement during DECEL Because of the Squirrely handling????
and You want OMG Traction coming OFF the corner....right????
The amount of Push...or loose conditions would determine other suspension adjustments accordingly...

Am I out in left field here??? or close or what...

Bill
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Old 10-01-2008, 05:35 PM   #94
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I don't want a front diff engaging during braking personally. Affects turn in too much, especially if trail braking, hence the torsen style front or 1.0 clutch
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Old 10-01-2008, 08:35 PM   #95
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I know the DCCD is really simply a 35/65 planetary gearset with an electric clutch. The planetary locks the split in at the 35/65. So, any time the clutch is not engaged, that's what you get. As it gets more voltage, the clutch starts to bind, essentially applying more torque to the front, up to a 50/50 split.

I know it's not automatically engaging because the rear of the car not only gets loose when the power comes in, but STAYS loose. As in, there is no adjustment in the power towards the front even after I would expect either the wheel speed sensors or the yaw sensor to have detected it and started engaging the clutch.

Mind you, I now know I'm part of the problem, and I need to get my brake lights to come on when the brakes actually engage so my left-foot-braking doesn't keep the DCCD open. Why the DCCD controller doesn't use a G-sensor to know when I'm braking (or turning) is beyond me.

That said, even if I keep my foot off the brake, I don't get that the diff is helping me. I know it works because I can set the manual dial and feel differences in the lock.
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Old 10-01-2008, 08:55 PM   #96
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Quote:
Originally Posted by Scooby South View Post
So to make sure I understand...

1. -You want "all" the diffs engaging during ACCEL....Correct...
2. -You want the Front, center and Rear to engage when coming "OFF" a corner...
3. -You don't want engagement during DECEL Because of the Squirrely handling????
4. and You want OMG Traction coming OFF the corner....right????

5. The amount of Push...or loose conditions would determine other suspension adjustments accordingly...

6. Am I out in left field here??? or close or what...

Bill
1. No
2. No
3. Depends
4. No
5. Yes
6. Yes

Hope that helps.
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Old 10-01-2008, 09:50 PM   #97
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Quote:
Originally Posted by Splash View Post
I know the DCCD is really simply a 35/65 planetary gearset with an electric clutch. The planetary locks the split in at the 35/65. So, any time the clutch is not engaged, that's what you get. As it gets more voltage, the clutch starts to bind, essentially applying more torque to the front, up to a 50/50 split.

I know it's not automatically engaging because the rear of the car not only gets loose when the power comes in, but STAYS loose. As in, there is no adjustment in the power towards the front even after I would expect either the wheel speed sensors or the yaw sensor to have detected it and started engaging the clutch.

Mind you, I now know I'm part of the problem, and I need to get my brake lights to come on when the brakes actually engage so my left-foot-braking doesn't keep the DCCD open. Why the DCCD controller doesn't use a G-sensor to know when I'm braking (or turning) is beyond me.

That said, even if I keep my foot off the brake, I don't get that the diff is helping me. I know it works because I can set the manual dial and feel differences in the lock.
Thanks for the explanation. I know you just said you've set the manual dial to feel the difference in lock, but have you specifically tried dialing it all the way back, inducing the wheel spin situation you're talking about, and then while the wheel is spinning, rolling it to lock to see what happens? I'm wondering if maybe the diffs aren't strong enough to stop the spin once it's started. Or maybe the ECU thinks "oh sh**, if I engage now it's just gonna burn the hell out of the clutch" or something? Just throwing some things out there.

What was the progression of sensor improvements? Was it yaw rate sensor in 05, and steering angle sensor in 06?

-Mike
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Old 10-01-2008, 10:53 PM   #98
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You are right about the sensor progression. In addition, the '06-'07 cars have a helical LSD in the center along with the electric clutch, and the planetaries are 41/59 instead of 35/65.

I haven't manually rolled it forward while the wheels are spinning, usually because I'm pretty busy trying to keep the rear from outrunning the front... <grin>

That said, locked all the way forward, it acts like you'd expect a 50/50 car to react, so I know the clutch can hold it. Now, can it hold it once it's spinning? That I don't know, but given the way the system works (sensors that detect spin before engaging the clutch), you'd think it was at least designed to.

I might try unplugging the brake light switch, but I run the risk there of having the center clutch engaging while trying to turn-in, which should make it push like a mother...
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Old 10-12-2008, 04:38 AM   #99
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Quote:
Originally Posted by Splash View Post
<snip>
Mind you, I now know I'm part of the problem, and I need to get my brake lights to come on when the brakes actually engage so my left-foot-braking doesn't keep the DCCD open. Why the DCCD controller doesn't use a G-sensor to know when I'm braking (or turning) is beyond me.
<snip>
Quote:
Originally Posted by Splash View Post
I might try unplugging the brake light switch, but I run the risk there of having the center clutch engaging while trying to turn-in, which should make it push like a mother...
Just for clarification, it's only the e-brake that puts the DCCD in open mode, not regular braking. There is a lateral G-Sensor, and a Yaw sensor in the 05 STi's DCCD logic. So doing anything with your brake light switch isn't going to do anything. The only the brake light the DCCD cares about is the one on the dash
The biggest input from the driver is throttle position, so left foot braking will still cause it to move towards more lock.

This graph shows how the data feeds into the DCCD to determine the lockup percentage, its from the 04 STi so it doesn't include the yaw sensor inputs which were added in 05:
http://forums.nasioc.com/forums/show...6&postcount=88
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Old 10-23-2008, 05:59 PM   #100
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A new front diff offering

http://forums.nasioc.com/forums/show....php?t=1623109

-Dylan @ DS1

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