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Old 12-07-2014, 07:53 PM   #1
Greg H
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Question on Rear Differential

Current Rule:
"Upgraded differential is permitted using a 3.46 gear ratio, factory housing, flanges, and mounting points.
The internal parts of the differential are otherwise unrestricted, including the use of limited slip units."
Based on my research the E46 330 did not come with a 3.46 differential. Manual trans was 2.93, and Auto trans was 3.38. The E46 325 automatic came with 3.46 ratio.

My question is; Can I use the 3.38 ratio from a 330, or must I find a 3.46 diff from a 325?

Greg Hartman

Last edited by Greg H; 12-07-2014 at 07:55 PM.
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Old 12-08-2014, 04:06 PM   #2
jtower
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Originally Posted by Greg H View Post
Can I use the 3.38 ratio from a 330
no

Last edited by jtower; 12-08-2014 at 04:06 PM.
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Old 12-08-2014, 07:14 PM   #3
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No problem, I have to buy one either way. This is my first build, so I was hoping for more info on the benefits of the 3.46, or why that was ratio was selected as the ratio of choice. I have a 2001 330i, manual, which has been my daily driver for the last 10 years. I plan to convert it to a SpecE46 over the next year.
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Old 12-18-2014, 06:22 PM   #4
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What differentials have been used in the existing builds?

Can you confirm model/transmission that the 3.46 came in?

Thanks you!
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Old 12-18-2014, 06:33 PM   #5
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contact dan at diffsonline, he's forgotten more about bmw diffs than most of us will ever know
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Old 12-18-2014, 06:44 PM   #6
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Most are not using stock bmw diffs. Buying aftermarket ones with the specs they want as long as it meets the rules.
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Old 03-29-2015, 10:44 AM   #7
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Will an m3 differential fit in a 330i ZHP?
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Old 03-29-2015, 05:06 PM   #8
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Originally Posted by Evanschro View Post
Will an m3 differential fit in a 330i ZHP?
no. and neither a M3 diff nor a ZHP is allowed in SE46, just so you know.
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Old 03-29-2015, 05:18 PM   #9
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What do you mean that it isn't allowed
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Old 03-30-2015, 09:31 AM   #10
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What do you mean that it isn't allowed
I hope you're not building a ZHP because unless the rule has changed recently that I am unaware the ZHPs are not allowed in the SE46.

But to answer your diff question.....an M3 diff does not have the 3.46 that you need. your options are to get an e30 325 diff. or an e85/86 Z4 diff which is probably our best bet due to price and how easy they are to find. there are a few random other selections but probably will be harder to find. I've included a link with all the gear ratios for a good majority of models. keep in mind that there are automatics listed as well so when youre looking just keep that in mind.

http://www.bokchoys.com/differential/GearRatios.htm
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Old 03-30-2015, 09:40 AM   #11
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What do you mean that it isn't allowed
Quote:
Originally Posted by the_iceman View Post
I hope you're not building a ZHP because unless the rule has changed recently that I am unaware the ZHPs are not allowed in the SE46.

But to answer your diff question.....an M3 diff does not have the 3.46 that you need. your options are to get an e30 325 diff. or an e85/86 Z4 diff which is probably our best bet due to price and how easy they are to find. there are a few random other selections but probably will be harder to find. I've included a link with all the gear ratios for a good majority of models. keep in mind that there are automatics listed as well so when youre looking just keep that in mind.

http://www.bokchoys.com/differential/GearRatios.htm

What's so very amusing is this brand new member (Evanschro) doesn't realize he's asking his question in a sub forum dedicated to SE46,........he's just asking this question just because, & it has nothing to do with him wanting to build a spec car.



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Old 03-30-2015, 09:42 AM   #12
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No problem, I have to buy one either way. This is my first build, so I was hoping for more info on the benefits of the 3.46, or why that was ratio was selected as the ratio of choice. I have a 2001 330i, manual, which has been my daily driver for the last 10 years. I plan to convert it to a SpecE46 over the next year.
I honestly dont know what went into the class creators decision to use this ratio however from what i understand (i could be completely wrong) the 3.46 will help with acceleration and put the car in the more usable power band. it also means that 5th gear is now a usable gear allowing for continued acceleration on longer straights. I dont know about anyone else but the OEM ratio in my car 5th gear is basically pointless on the track. I'm guessing they wanted to correct that. the trade off is a lower top speed although how much i dont know because i have yet to drive one installed. Maybe someone can confirm this who is already running with it???

also this is just based on my own research as i am starting my build so if i am totally wrong please someone correct me.

Last edited by the_iceman; 03-30-2015 at 09:55 AM.
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Old 03-30-2015, 07:51 PM   #13
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Ya I just had a question
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Old 04-01-2015, 11:08 AM   #14
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Originally Posted by the_iceman View Post
I honestly dont know what went into the class creators decision to use this ratio however from what i understand (i could be completely wrong) the 3.46 will help with acceleration and put the car in the more usable power band. it also means that 5th gear is now a usable gear allowing for continued acceleration on longer straights. I dont know about anyone else but the OEM ratio in my car 5th gear is basically pointless on the track. I'm guessing they wanted to correct that. the trade off is a lower top speed although how much i dont know because i have yet to drive one installed. Maybe someone can confirm this who is already running with it???

also this is just based on my own research as i am starting my build so if i am totally wrong please someone correct me.
I have experience on this subject: my e46 had a 3,46 LSD fitted.

3,46 is the most common differential avail in the non-M e46 world; virtually 1/2 the automatic cars had it. finding a core unit should not be a problem for most SE46 racers as you WILL need to have a spare in your trailer - BMW does NOT sell new bearings/races for these units intentionally.

Most competitive NASA GTS/BMW IP club racers here in nor-cal are running 3,91 final drive with 7,000rpm engines and 4,10 with 8,000 rpm engines. 3,46 will be too long for the elevations at Laguna Seca and Sonoma but likely good for Big willow and Road america, TWS, etc

Quote:
Originally Posted by Greg H View Post
Current Rule:
"Upgraded differential is permitted using a 3.46 gear ratio, factory housing, flanges, and mounting points.
The internal parts of the differential are otherwise unrestricted, including the use of limited slip units."
Based on my research the E46 330 did not come with a 3.46 differential. Manual trans was 2.93, and Auto trans was 3.38. The E46 325 automatic came with 3.46 ratio.

My question is; Can I use the 3.38 ratio from a 330, or must I find a 3.46 diff from a 325?

Greg Hartman
if the spec class is set to 3,46 its a good overall compromise for all tracks; also cost effective to obtain spares for. This is the same reason why SE30 has the original 3,73 final drive as the "spec" ratio

What you actually put in your car is your own choice; wording seems to allow for Not upgrading and using the original open diff and 3,38.
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Last edited by wanganstyle; 04-01-2015 at 11:10 AM.
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Old 05-03-2015, 07:21 PM   #15
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Why are the diffs so damn expensive? That was one of the factors that almost turned me off from building a SE46. And I still haven't purchased anything yet as I'm trying to understand this more and either answer my own question and figure out a "cheaper" way to get a good diff, or I'll wind up spending the money anyways....

Last edited by POINTBY; 05-03-2015 at 07:22 PM.
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Old 05-05-2015, 12:53 AM   #16
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Why are the diffs so damn expensive? That was one of the factors that almost turned me off from building a SE46. And I still haven't purchased anything yet as I'm trying to understand this more and either answer my own question and figure out a "cheaper" way to get a good diff, or I'll wind up spending the money anyways....
if you want to be "cheap" a M-factory unit is under 1k. This might not produce desired lap times though; the only reason there is a demand for aftermarket differentials is lap time.
Any given NASA weekend here in Norcal there will be a variety of aftermarket very customized LSD differential units on the podium.
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Last edited by wanganstyle; 05-05-2015 at 12:55 AM.
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Old 05-06-2015, 09:40 AM   #17
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the only reason there is a demand for aftermarket differentials is lap time.
Definitely one of the biggest reasons, and that applies to just about every part you'd want to think about installing/replacing on the car, especially in a spec series.

Longevity and customization are other huge reasons to go with a solid differential choice. A properly setup diff design results in more active surfaces for better handling (turn-in and putting power down through the exit) plus the ability to optimize ramp angles for less preload lock and better mid-corner speed. Utilizing REM-polished gears and carrier bearings will make for lower operating temperatures (longevity) and lower friction (less drivetrain loss = more "power" to the ground).
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Old 05-10-2015, 11:30 AM   #18
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Definitely one of the biggest reasons, and that applies to just about every part you'd want to think about installing/replacing on the car, especially in a spec series.

Longevity and customization are other huge reasons to go with a solid differential choice. A properly setup diff design results in more active surfaces for better handling (turn-in and putting power down through the exit) plus the ability to optimize ramp angles for less preload lock and better mid-corner speed. Utilizing REM-polished gears and carrier bearings will make for lower operating temperatures (longevity) and lower friction (less drivetrain loss = more "power" to the ground).
A gear type differential would also accomplish all of the above ( at the lack of ability to preform in wheel lift situations like a clutch type unit). Obviously total lockup does not happen besides for a Torsen-Gleason.

Vintage era an am racing involved many TORSEN-GLEASON units. Sadly none avail for BMW applications; perhaps bimmerworld could look into it for the future; )

The os units and highly modified zf units are quite popular among the NASA crowd. A stock ZF can suffice but is honestly barely adequate.

In GTS3/4 you almost need an aftermarket Japanese unit to be competitive; it's about 0.5 seconds a lap average depending on track here; the real advantages in aftermarket units like Cusco, OS, is the dampening of lockup with internal mechanisms.
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Last edited by wanganstyle; 05-10-2015 at 11:31 AM.
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Old 05-13-2015, 08:17 AM   #19
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A gear type differential would also accomplish all of the above ( at the lack of ability to preform in wheel lift situations like a clutch type unit). Obviously total lockup does not happen besides for a Torsen-Gleason.

Vintage era an am racing involved many TORSEN-GLEASON units. Sadly none avail for BMW applications; perhaps bimmerworld could look into it for the future; )

The os units and highly modified zf units are quite popular among the NASA crowd. A stock ZF can suffice but is honestly barely adequate.

In GTS3/4 you almost need an aftermarket Japanese unit to be competitive; it's about 0.5 seconds a lap average depending on track here; the real advantages in aftermarket units like Cusco, OS, is the dampening of lockup with internal mechanisms.
Would you choose say a torsen Wavetrac over a traditional 3 clutch unit for road racing?
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Old 05-16-2015, 11:53 PM   #20
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Would you choose say a torsen Wavetrac over a traditional 3 clutch unit for road racing?
I never use 3 clutches for circut. Only 2 or 4 or 20+ in Japanese units.

(I run a CUSCO HYBRID in my own e36)

Wavetrac is good and only recommended for automatic street cars.
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