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Old 12-09-2001, 05:08 AM   #1
chiraoka
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Question Billet RWD Conversion centre diff

Looking at Cobb Tuning web site, I came across their "garage sale", there I saw this Billet RWD conversion centre diff.
I have been interested on RWD WRX for a while now, cause AWD cars are banned on all of out national circuit series.
Does anyone have any previous experience with one of this conversion centre diff's ..... ?
I would also like to know what are the power losses in comparison to the stock AWD system, should be interesting to see how does the stock gearbox work sending all of the power to the rear diff.

Carlos Hiraoka
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Old 12-09-2001, 01:15 PM   #2
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I don't think it is a good idea. The reason is because Auto-makers have engineered each axle (either the rear or the front) to take a percentage of the power for most of the time. In case of the Manual Subarus and Automatic WRXs, the front and the rear axles are designed to take 50% of the power most of the time. They are definitely not designed to take 100% of the power, 100% of the time. If you make the car into a RWD vehicle, essentially 100% of the car's power is taken by the rear axle, all the time. It will fail before long.

Later...AH
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Old 12-09-2001, 02:05 PM   #3
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That would make sense, except for the fact that the Auto Trannied Imprezas transfer 90% of the HP/torque to one set of axles under load conditions .

Brian
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Old 12-09-2001, 02:09 PM   #4
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Well, in order for the axles to mount into the R180 rear diff, they would have to be of the proper size. I would say as long as your power is within the limits of the R180 (400-500, depends which nissan site you want to believe I guess), you should be ok..axle wise.

It would be nice if you could get rid of the front axles! Pity =(
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Old 12-09-2001, 07:36 PM   #5
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Conduit: my rear diff is the R180, I don't know if the MY01 WRX's come with this rear diff, but is bigger than the stock WRX one (MY 98 - 00) it is the same rear diff as on the Nissan Sylvia so it should handle the power.

Like I was telling AWD is prohibited on any national series here ..... therefore I was looking into this option, just wanted to get any kind of information or feedback on this "Billet RWD conversion kit" ..... I wanted to know how effective is this especially regarding power loss due to the centre diff.
Cusco runs a RWD WRX and works fine ..... definetly you'll have to look at other spring rates and struts setting, also probably the diameter of the roll bars, but should work.

Carlos H.
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Old 12-10-2001, 03:39 AM   #6
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Don't forget also your suspension is tuned for an all-wheel drive car, a rear wheel drive impreza is kinda a oversteer always car, and without major suspension work will also be a spin the wheels always car. Ask Trey last I hear when he had the car rwd is would oversteer very easy on the power or off of it. Better yet ask some 2.5RS Turbo guys who converted to rwd for dyno runs and were getting wheel spin on the highway in 3rd or 4th I forget but still..... , that said with enough time and money invested a rwd impreza could be a sweet car
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Old 12-10-2001, 11:44 AM   #7
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Thumbs up

Jeff, I too think that the WRX can be a "interesting" RWD, if done properly. Were the guys running 2.5 RS turbo's with a LSD on the rear diff ?????

Obviously a much wider tyre and wheels will be needed for the rear axle. Doesn anyone know if the transmission losses are greater on a RWD or AWD WRX ?

Carlos H.
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Old 12-10-2001, 12:49 PM   #8
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Carlos, I would assume the drivetrain loss would be less on a RWD Impreza in that you aren't getting any frictional losses at the front diff anymore.

- Trent
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Old 12-10-2001, 01:49 PM   #9
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Quote:
Originally posted by North Ursalia
That would make sense, except for the fact that the Auto Trannied Imprezas transfer 90% of the HP/torque to one set of axles under load conditions .

Brian
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You are correct. But in the Auto-trannied Imprezas/Subarus (except the Auto-trannied WRX !!!), the front axle is designed to take 90% of the torque 90% of the time. If you were to look closer, you will find that the rear axle will not be as durable as the front axle, in those Imprezas/Subarus.

This principle you can find mostly in cars that began life as a FWD or a RWD car and then was converted to AWD. If you notice the Mercedes 4-matic, the power bias will be to the rear, since the rear axle in the 2-wheel drive variant has been engineered to take 100% of the torque 100% of the time. Same would apply to the Porsche AWD variant of the 911. They just added an additional axle in the other end, to handle some amount of power/torque for short durations of time.

On the contrary, you will find the reverse in case of cars like the Acura MDX, where you will find the power biasing to the front wheels? This is because, it is based on the FWD Odyssey, where the front axle has been engineered to handle 100% of the torque/power 100% of the time.

The "other axle" in case of the AWD variant of the 2-wheel drive car, can and do handle additional power/torque as needed, but definitely not for long durations of time, since it does not make sense from a cost/benefit perspective, to design both the axles to handle 100% of the power 100% of the time, since such a set-up would probably way outlast the normal life of the car!!!

Later...AH
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Old 12-10-2001, 02:43 PM   #10
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BTW old STi's like mine come original with 80% rear / 20% front power distribution.
That is also why mine has a larger rear diff (same as the Sylvia unit)

Carlos H.
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Old 12-11-2001, 04:03 AM   #11
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The new WRX uses the R180, it looks virtually identical to the R180 in my 200SX Turbo. BTW, Nissan makes a very nice rear diff housing that's finned, holds 4 quarts and is tapped for a cooler

If you need custom axles, I'm local to Raxles. If you search around, you will find him to be a preeminent source of axles in alot of car communities. The guy is seriously top notch. There is a story of some prostock guys blowing some custom axles at the Gatornationals, and Raxles had them back on the track the next day. He also made the custom axles on my buddy's D16 turbo swapped 79 civic. Pretty trick stuff.

ANYWAY, the point is, with Raxles here, I'd be happy to go talk to Marty about anything any I-club members may need from him
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Old 12-11-2001, 09:18 AM   #12
chiraoka
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Thumbs up THANX !

Conduit: thanx for your reply and info, I have seen on the STi catalogue that they also make a larger housing, but definetly it is easier and probably less $$$ to get the Nissan part (just hope it fits, it should .....)
Regarding the axles, I have compared both the 200sx axles with mine and they are the same width, so they should be able to cope upto 350hp, if more power comes then definetly I will be looking to custom axles, it could be very nice to already start having RAXLES giving us an aprox. price on upgraded axles for the rear and front WRX axles.
Once again thanx for your reply, I should be posting more as I progress with this project.

Carlos H.
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Old 12-13-2001, 12:05 PM   #13
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As soon as I get break in the start of January, I'll go chat with Marty about axles (before, if I get time!). I'm sure he will have useful information!
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Old 01-07-2002, 08:02 PM   #14
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word on the street is alota the aussies have modified RWD wrx's mab scoop around mrt or such. also in japan gt300 there is a RWD impreza that does decent, its currently still running, so u may wanna check out that. i forgot what team, may be cusco, but im not sure.

h
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Old 01-08-2002, 08:04 PM   #15
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Does anyone know what they do with the fronts? Do they just leave them in, or can you somehow just remove the front diff and such? I know you would have to seal the holes with some covers.
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