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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > does the 335Xi have the option to be RWD like an STI?



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      06-27-2011, 05:36 PM   #221
bpas328xi
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Quote:
Originally Posted by aakrusen View Post
I think it will improve your MPG because the only the rear wheels are putting resistance on the system. Look at it like a 4wd truck. Put the truck in 4wd and your mileage goes down. Put it back in 2wd and the mileage gets better. Now the increase in mileage might not be spectacular, it should be an improvement.
Fueleconomy dot gov says that the 335xi gets 17 city and 25 highway. For the 335i it says 18 city and 26 highway.
Yeah, but you are comparing an i to an xi. The xi has a front diff that stays engaged. All you're doing here with the fuse is disabling the front output. Unless you have disengaging hubs, which the xi does not have, you're still going to be spinning the front drive components and you will still have the same amount of drag. If you read through the thread, people have said that the front output of the transfer case disengages at highway speeds anyway.

So, I predict no improvements in mpg. Change out the intake, that'll give you better mpg.
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      06-27-2011, 05:58 PM   #222
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Quote:
Originally Posted by bpas328xi View Post
Yeah, but you are comparing an i to an xi. The xi has a front diff that stays engaged. All you're doing here with the fuse is disabling the front output. Unless you have disengaging hubs, which the xi does not have, you're still going to be spinning the front drive components and you will still have the same amount of drag. If you read through the thread, people have said that the front output of the transfer case disengages at highway speeds anyway.

So, I predict no improvements in mpg. Change out the intake, that'll give you better mpg.
I don't know what highway speeds you are going at, but it turns RWD at 100mph, not highway speeds.

I think there will be an increase in gas mileage, however, it will not be noticeable. It will be very slight. You will see the increase because the clutch transferring power to the front will be open, i.e. no friction losses, but you still have the weight from the AWD system. It might be somewhere between an i and xi, leaning a little more towards the xi I would think.

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      06-27-2011, 06:35 PM   #223
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      06-27-2011, 06:41 PM   #224
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Quote:
Originally Posted by blauner335 View Post
I don't know what highway speeds you are going at, but it turns RWD at 100mph, not highway speeds.

I think there will be an increase in gas mileage, however, it will not be noticeable. It will be very slight. You will see the increase because the clutch transferring power to the front will be open, i.e. no friction losses, but you still have the weight from the AWD system. It might be somewhere between an i and xi, leaning a little more towards the xi I would think.

Update on my status:
I am taking tons of data at the moment and trying to reverse engineer some things. I can see the light at the end of the tunnel. This is really getting fun
I.think that I might be working at this from a different direction to you.
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      06-27-2011, 07:25 PM   #225
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sorry a little late but.........
an sti cannot be dialed in to 100% rwd unless you do a full rwd conversion
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      06-27-2011, 07:32 PM   #226
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I'm really looking forward to this I along with probably everybody else in here appreciate all the hard work you are doing to make this happen.
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      06-28-2011, 09:19 PM   #227
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OK, jacked the rear end up and let the clutch out slowly and only the rears turned, the fronts did not and did not pull the car on the jack. ? AWD disconnected (goes to 0%) below a certain mph? ?5-10mph?
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      06-28-2011, 11:47 PM   #228
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Quote:
Originally Posted by CobraMarty View Post
OK, jacked the rear end up and let the clutch out slowly and only the rears turned, the fronts did not and did not pull the car on the jack. ? AWD disconnected (goes to 0%) below a certain mph? ?5-10mph?
Don't let your insurance company see your post. Come on! Think about it. If the AWD drive didn't work below 5 mph, then it wouldn't work from a dead stop, like getting going in snow, so the answer to your question: does it disconnect below a certain speed? The answer is no.
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      06-29-2011, 12:08 AM   #229
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Then explain the results. It does makes sense, trying to turn a locked AWD/4WD at low speed is not fun. Maybe the AWD has an algorithm where it must see ?10 revolutions of the rear tires, ? see less than 32 degrees outdoors? But today at 85 degrees and 0mph and rears only rotate 5 revoltions then it stays at 0% and the fronts did not move.
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      06-29-2011, 12:19 AM   #230
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Quote:
Originally Posted by CobraMarty View Post
Then explain the results. It does makes sense, trying to turn a locked AWD/4WD at low speed is not fun. Maybe the AWD has an algorithm where it must see ?10 revolutions of the rear tires, ? see less than 32 degrees outdoors? But today at 85 degrees and 0mph and rears only rotate 5 revoltions then it stays at 0% and the fronts did not move.
10 revolutions and you would be stuck in mud, sand or snow. The AWD kicks in IMMEDIATELY when slip is detected.
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      06-29-2011, 12:52 AM   #231
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Send a message via AIM to klov335
Xi needs to be lowered, cornering feels like a boat
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      06-29-2011, 08:15 AM   #232
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Quote:
Originally Posted by 4corners View Post
10 revolutions and you would be stuck in mud, sand or snow. The AWD kicks in IMMEDIATELY when slip is detected.
I am just asking a question. How do you explain my findings.
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      07-03-2011, 11:22 AM   #233
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      07-03-2011, 02:15 PM   #234
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VERY interesting...subscribed!
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      07-11-2011, 10:35 AM   #235
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      07-11-2011, 11:04 AM   #236
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+1
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      07-15-2011, 08:55 PM   #237
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check this out: http://www.autoblog.com/2011/07/15/2...-crazy-burnou/

jeep srt-8 can be programmed to send 100% of the power to the rear wheels through software. can't wait to hopefully do that with ours someday!
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      07-25-2011, 09:04 AM   #238
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We need this before the end of summer
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      08-04-2011, 12:55 PM   #239
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any update?
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      08-04-2011, 01:23 PM   #240
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Quote:
Originally Posted by CobraMarty View Post
I am just asking a question. How do you explain my findings.
"In its resting state, a clutch outputting to the front axle sits opens, sending 100 percent of power to the vehicle's rear axle."

http://reviews.cnet.com/2300-10863_7...s=1&o=10004657
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      08-17-2011, 10:34 AM   #241
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Wink

Bump and some confirmed information that has been floating around for some time. Right from BMW training manuals:

Quote:
Permanent all-wheel drive is cancelled to a large extent or completely in only three control situations:
• When negotiating extremely tight corners with little engine torque in order to allow speed equalization between the front and rear axle (e.g. parking)
• At speeds in excess of 180 km/h
• In extreme understeer driving situations
Also, interesting finding:

Quote:
There is also a temperature sensor installed in the motor that signals the temperature to the transfer case control unit (VGSG). A temperature model is calculated in the VGSG for the purpose of protecting the motor from
overload. For this purpose, the maximum closing rate is reduced in various stages. If these measures are not sufficient to protect the motor from overload, the control is interrupted and the clutch completely opened so that only rear axle drive is now possible.
Source: http://www.bawarec.ru/manuals/5er/e6...5er-e60-12.pdf
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      08-17-2011, 01:54 PM   #242
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Has anyone tried this awd to rwd trick to do a dyno?
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