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Old 05-11-2004, 04:20 PM   #1
Glory22
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Gears on a BMW?

I'm curious...can you put a set of gears on a BMW to help it's acceleration off the line? A buddy of mine has a new Mustang GT, and he's putting a set of gears on to help in acceleration. I know you can spend a fortune to supercharge a 323ci, and get a dinan chip...would gears work? If so has anyone done this?

Thanks!
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Old 05-11-2004, 04:25 PM   #2
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it costs a bigger fortune to purchse the new gear sets. on tope of that they are hard to find and then you have to have them installed. etc.

s/c is cheaper
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Old 05-11-2004, 04:35 PM   #3
slow323ci
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Sure. Many people on these forums have done it, including me. Except with a BMW, you change the whole diff assembly rather than the gears inside it.

I swapped my original 3.07 differential for a 3.46. Made a huge difference.

Do a search for "differential" and you'll see dozens of threads about this.

P.S. - It's not even expensive - my swap cost less than $460 for parts and labor. The parts were from a wrecked 323.
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Old 05-11-2004, 04:50 PM   #4
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Quote:
Originally Posted by slow323ci
Sure. Many people on these forums have done it, including me. Except with a BMW, you change the whole diff assembly rather than the gears inside it.

I swapped my original 3.07 differential for a 3.46. Made a huge difference.

Do a search for "differential" and you'll see dozens of threads about this.

P.S. - It's not even expensive - my swap cost less than $460 for parts and labor. The parts were from a wrecked 323.

I think he was talking about the gears in the transmission... but I could be wrong.
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Old 05-11-2004, 05:32 PM   #5
slow323ci
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Quote:
Originally Posted by notE46
I think he was talking about the gears in the transmission... but I could be wrong.
Nah... When a Mustang guy (or anyone with a muscle car or hot rod) says he "got gears" that means in the differential.
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Old 05-11-2004, 06:00 PM   #6
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when you say gears to get off line faster you mean

rear gears in the diff. i agree get 346 gears they are not that costly. not like
the ones for my m3 411 and 433 they will cost 3,000.00 to buy and install
if you put in the 346 gears you will get a good bang for your dollar. they will give you in the neigberhood of 20% more torq. from what you have already.
you won't be a burner but you will move faster it is worth the money in the case of the 346 gears. look in the for sale forum you just might see a set of does gears for sale.
bobm3
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Old 05-11-2004, 06:48 PM   #7
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I just swapped the stock 2.93 diff in someone's 328 with a 3.15 from a 325.


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Old 05-11-2004, 07:55 PM   #8
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Quote:
Originally Posted by teamdfl
I just swapped the stock 2.93 diff in someone's 328 with a 3.15 from a 325.


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How much did that 3.15 come to if you dont mind me asking? They seem to be alot more than 3.46s.
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Old 05-11-2004, 08:49 PM   #9
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Originally Posted by bbh03
How much did that 3.15 come to if you dont mind me asking? They seem to be alot more than 3.46s.
I have no idea how much it cost. I think the owner of the car bought it from someone who installed a 3.46 to replace the 3.15.


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Old 05-11-2004, 08:51 PM   #10
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I hear ppl at my school w/ camaros saying "I got me a 4.10 gear"...no, you didnt. You got a new differential. Sorry, that just annoys me. I had to tell someone.

Simsima got a new differential and I remember reading that he said it make all the difference in the world. The RPMs are just higher when cruising on the highway.
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Old 05-11-2004, 09:00 PM   #11
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Quote:
Originally Posted by teamdfl
I just swapped the stock 2.93 diff in someone's 328 with a 3.15 from a 325.


Ed

No regrets at all? Like is 1st gear too short now? Does the car rev too high on the highway?
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Old 05-11-2004, 09:19 PM   #12
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Originally Posted by Amalfi
No regrets at all? Like is 1st gear too short now? Does the car rev too high on the highway?
Again, it's not my car. From what I've heard, the owner loves it and has zero regreats. He said the minor change in revs (7.5%) on the highway is barely noticeable.
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Old 05-11-2004, 09:43 PM   #13
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Thanks for all your replies guys!

I was talking about the differential gear replacement. What do the numbers of the gears mean...like 3.07, or 3.46? Are 3.46 gears made by BMW or are they aftermarket. Also, if i switch to these gears does it make the car unreliable or anything?

"Slow323ci": What exactly did you do to your 323ci, besides the gears in order to make it quick? I have the same model car and i'm looking to modify in order to make it a little quicker.

Thanks for your help!
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Old 05-11-2004, 09:54 PM   #14
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Swapping the gearset inside the differential assembly (a.k.a. the final drive) is possible but requires some critical shimming to set gear mesh and bearing preload. It is usually much cheaper to find a complete used differential assembly from another BMW with the desired gearset already installed. All non-M E46 differential assemblies are interchangeable. At most you may have to swap output flanges which may only require a couple long screwdrivers for leverage. They are held in only by a wire clip and are easily pried out.

The number is a gear ratio determined by the number of teeth of the ring gear (output) vs. the pinion gear (input). For example: 41 teeth on the ring gear and 13 teeth on the pinion give you a 3.15 ratio. 41/13=3.153846 3.15 is close enough. That means that for every 3.15 turns of the driveshaft, the axles will turn once.

Your car will not be less reliable with a lower gear (higher numerically). At worst, you will increase the RPMs at any given speed which will probably drop a couple MPG off your gas milage.



Quote:
Originally Posted by Glory22
Thanks for all your replies guys!

I was talking about the differential gear replacement. What do the numbers of the gears mean...like 3.07, or 3.46? Are 3.46 gears made by BMW or are they aftermarket. Also, if i switch to these gears does it make the car unreliable or anything?

"Slow323ci": What exactly did you do to your 323ci, besides the gears in order to make it quick? I have the same model car and i'm looking to modify in order to make it a little quicker.

Thanks for your help!
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Old 05-11-2004, 10:28 PM   #15
slow323ci
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Quote:
Originally Posted by Glory22
"Slow323ci": What exactly did you do to your 323ci, besides the gears in order to make it quick? I have the same model car and i'm looking to modify in order to make it a little quicker.

Thanks for your help!
Hmmm, things I did to make my 323 quicker, in order of improvement:

- 3.46 differential swap made by far the biggest difference
- Conforti Shark software
- Conforti intake
- Borla exhaust
- Plasma Direct ignition coils

BTW, if your 323 is an automatic you already have the 3.46 diff.

I easily outran a Porsche 968 the other day. I'm not sure how fast those are though.
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Old 05-11-2004, 11:06 PM   #16
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Quote:
Originally Posted by cowmoo32
I hear ppl at my school w/ camaros saying "I got me a 4.10 gear"...no, you didnt. You got a new differential. Sorry, that just annoys me. I had to tell someone.
Don't think so. When they say that got a 4.10 gear, that's what they got: a new ring and pinion gear with a ratio 4.10, not a new differential. There is a lot more to a differential then just those two gears.

Mike
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Old 05-12-2004, 09:57 AM   #17
Glory22
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Yeah, mine's an automatic with steptronic....that means i already have the 3.46 gear ratio? So there's nothing i can really do to the differential then i guess
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Old 05-12-2004, 11:37 AM   #18
slow323ci
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Quote:
Originally Posted by Glory22
Yeah, mine's an automatic with steptronic....that means i already have the 3.46 gear ratio? So there's nothing i can really do to the differential then i guess
Yes, you already have the 3.46. Nothing you can do...
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Old 05-12-2004, 12:33 PM   #19
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Originally Posted by slow323ci
Yes, you already have the 3.46. Nothing you can do...
3.64 from a Z4 2.5
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Old 05-12-2004, 12:35 PM   #20
Glory22
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Have you done that to your car? changing to a z4 differential...
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