Differential Confusion - Bimmerfest - BMW Forums



Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 3 Series & 4 Series > E46 (1999 - 2006)

E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

Reply
 
Thread Tools Display Modes
  #1  
Old 07-06-2020, 11:53 AM
meinbills meinbills is offline
Officially Welcomed to the 'Fest
Location: Wisconsin
 
Join Date: May 2017
Posts: 778
Mein Auto: 2001 325ci/2003 330i
Differential Confusion

So I have a 5-speed manual with a manual diff I think because when I cruise at 80 mph, the rpm is at 3200. Wish to bring the rpm down so is swapping the diff and not changing the transmission an option? if so, what diff should I look for? I think my confusion is when the numbers are thrown around and not understanding how they relate. Is a lower ratio diff the one for me or a higher ratio one? Thanks.
Reply With Quote
Sponsored Links
Advertisement
 
  #2  
Old 07-06-2020, 12:37 PM
lgr122's Avatar
lgr122 lgr122 is online now
Officially Welcomed to the 'Fest
Location: Finland
 
Join Date: Aug 2012
Posts: 2,023
Mein Auto: '04 e46 Touring M-Sport
Smaller number in differential means you go faster with same rpm.
__________________
'04 e46 Touring M54, at work '19 VW Van, wife has '05 e87 M47
Reply With Quote
  #3  
Old 07-06-2020, 12:38 PM
Doug Huffman's Avatar
Doug Huffman Doug Huffman is offline
Nuclear engineer
Location: Washington Island, Wisconsin, thru Death's Door
 
Join Date: Apr 2015
Posts: 15,972
Mein Auto: CPO2012 X5 35d M57(E70)
Gear ratios and differential ratios are the turns of input / turns of output. The drive pinion is the 'little' gear and the ring is the 'big' gear. It takes "ratio" turns of the pinion to make the ring go around once.
__________________
Scepticism and Animal Faith (1923)
Scepticism is the chastity of the intellect, and it is shameful to surrender it too soon or to the first comer: there is nobility in preserving it coolly and proudly through long youth, until at last, in the ripeness of instinct and discretion, it can be safely exchanged for fidelity and happiness.
(The Works of George Santayana p. 65)

Eschew eristical argumentation. I am responsible for what I write, not for your understanding of it.
Reply With Quote
Sponsored Links
Advertisement
 
  #4  
Old 07-06-2020, 01:14 PM
JKRIT JKRIT is offline
Officially Welcomed to the 'Fest
Location: Hollis, NH
 
Join Date: Feb 2008
Posts: 1,272
Mein Auto: '03 525i
Meinbills: You may find this chart useful: http://www.bokchoys.com/differential/GearRatios.htm
If you are talking about a 325ic, then it looks like you have a 3.15 dif (which is rather rare, I found). You could go down to a 3.07, which you probably wouldn't notice, or a 2.93. Our touring came with a 3.46, apparently for drag racing or towing a trailer (sarc: off now). I ordered the only used 3.15 I could find, but recieved a 3.07 instead. Decided to put it in anyway and am very happy. Still launches without bogging, and is quieter on the highway. Wasn't looking for MPG change and didn't get it.
__________________
'12 328i Cab Deep Sea Blu/Tan
'03 525i Sapphire Blu/Grey, SP, Nav
'03 530i Sterling Gray/Blk, SP
'02 325it Orient Blu/Grey, SP, Nav
Reply With Quote
  #5  
Old 07-06-2020, 05:17 PM
meinbills meinbills is offline
Officially Welcomed to the 'Fest
Location: Wisconsin
 
Join Date: May 2017
Posts: 778
Mein Auto: 2001 325ci/2003 330i
So in summary, I should get a 2.x diff to keep my rpm down while cruising on the freeway. JKRIT, I have a 330i 5-speed manual. From that link you posted, this is my transmission

1st 4.21
2nd 2.49
3rd 1.66
4th 1.24
5th 1.00

final drive 2.93

What do these numbers mean? Would putting in a lower-ratio diff "improve" the final drive number (lowering it or increasing it?) so that my rpm drops lower at the same speed? Sorry, I am not too smart in this area.
Reply With Quote
  #6  
Old 07-06-2020, 07:32 PM
Fast Bob's Avatar
Fast Bob Fast Bob is online now
Keeping it surreal
Location: Here, there, everywhere....
 
Join Date: Jun 2004
Posts: 42,951
Mein Auto: 2004 330Ci ZHP 3 pedals
This can be a bit confusing for the uninitiated, because in gearing, the terms "lower" and "higher" might mean exactly the opposite of what you think they would mean.

So, evidently, you currently have (supposedly) a 3.15 diff. If you were looking to improve acceleration numbers, folks here would probably say "You need a lower diff ratio", which would indicate something like a 3.46, which might be higher numerically, but will spin the engine at a higher RPM at the same speed compared to that old 3.15 rear.

Alternatively, if you were looking to drop your cruising RPMs (as you are now), you would be advised "You need higher gears", like either a 3.07, or 2.93, which are lower numerically, but both will drop the cruising RPMs just a tad (in your case, only about ~5% or 7%, hardly worth the effort to change everything).

Factory engineers spent a sh!tload of time and R&D money to provide us with the best compromise in gearing, to best utilize the limited torque and HP that these engines offer, and you will not have much hope of improving on that !
__________________
The road goes ever onward....
(R.I.P. Jever)

*Please support the Disabled American Veterans*

When faced with choosing between two evils, always go with the one you`ve never tried before....
Reply With Quote
  #7  
Old 07-06-2020, 08:50 PM
meinbills meinbills is offline
Officially Welcomed to the 'Fest
Location: Wisconsin
 
Join Date: May 2017
Posts: 778
Mein Auto: 2001 325ci/2003 330i
So are you saying that no matter what diff i use, with my 5-speed and best case scenario of 7%, I would only shave 210 RPM off my 3200 RPM @ 80 MPH? is it because of my 5-speed? I've read other posts saying that they got 2500 RPM at 80 MPH but I think they have 6-speed.
Reply With Quote
  #8  
Old 07-06-2020, 09:36 PM
Fast Bob's Avatar
Fast Bob Fast Bob is online now
Keeping it surreal
Location: Here, there, everywhere....
 
Join Date: Jun 2004
Posts: 42,951
Mein Auto: 2004 330Ci ZHP 3 pedals
Quote:
Originally Posted by meinbills View Post
So are you saying that no matter what diff i use, with my 5-speed and best case scenario of 7%, I would only shave 210 RPM off my 3200 RPM @ 80 MPH? is it because of my 5-speed? I've read other posts saying that they got 2500 RPM at 80 MPH but I think they have 6-speed.
Bingo....gearing differences between the 5-speed and 6-speed trannies are minimal (if any), the main difference is that the additional (6th) gear gives you a 15% overdrive, which relates to a more relaxed highway cruise....

Another thing to consider is that installing a numerically lower (2.93, etc.) diff will have the effect of reducing available torque, making the car feel more sluggish going through the gears....
__________________
The road goes ever onward....
(R.I.P. Jever)

*Please support the Disabled American Veterans*

When faced with choosing between two evils, always go with the one you`ve never tried before....
Reply With Quote
  #9  
Old 07-07-2020, 05:17 AM
meinbills meinbills is offline
Officially Welcomed to the 'Fest
Location: Wisconsin
 
Join Date: May 2017
Posts: 778
Mein Auto: 2001 325ci/2003 330i
So the only way to go is to switch to a 6-speed, since I think I have the 2.93 diff. Should be doable, right? This sounds more complicated than a diff swap.
Reply With Quote
  #10  
Old 07-07-2020, 05:28 AM
SPDSKTR SPDSKTR is offline
I'm a DlCK! So what?
Location: Birmingham, AL, USA
 
Join Date: Sep 2011
Posts: 3,584
Mein Auto: E46 ZHP TS2+ Coupe
If you have a non-ZHP 330Ci with a manual transmission, you have a 2.93.

Yes, transmission swaps are far more complex than differential swaps.
Reply With Quote
  #11  
Old 07-07-2020, 05:41 AM
meinbills meinbills is offline
Officially Welcomed to the 'Fest
Location: Wisconsin
 
Join Date: May 2017
Posts: 778
Mein Auto: 2001 325ci/2003 330i
Non-zhp 330i, not 330ci.
Reply With Quote
  #12  
Old 07-07-2020, 06:22 AM
SPDSKTR SPDSKTR is offline
I'm a DlCK! So what?
Location: Birmingham, AL, USA
 
Join Date: Sep 2011
Posts: 3,584
Mein Auto: E46 ZHP TS2+ Coupe
Quote:
Originally Posted by meinbills View Post
Non-zhp 330i, not 330ci.
You have a 2.93, which is the tallest available non-custom differential for the E46.
Reply With Quote
  #13  
Old 07-07-2020, 06:49 AM
meinbills meinbills is offline
Officially Welcomed to the 'Fest
Location: Wisconsin
 
Join Date: May 2017
Posts: 778
Mein Auto: 2001 325ci/2003 330i
OK, a 6-speed swap it is. Not sure I wan to tackle the project but how much does it cost for the swap, low and high at an indie shop?
Reply With Quote
  #14  
Old 07-07-2020, 07:16 AM
meinbills meinbills is offline
Officially Welcomed to the 'Fest
Location: Wisconsin
 
Join Date: May 2017
Posts: 778
Mein Auto: 2001 325ci/2003 330i
Just a thought, so if I could get another e46 330 6-speed, then is it just as simply as take out the old tranny and put in the new one, no need for other changes, right? If so then I have to scour the salvage yards.
Reply With Quote
  #15  
Old 07-07-2020, 08:22 AM
JKRIT JKRIT is offline
Officially Welcomed to the 'Fest
Location: Hollis, NH
 
Join Date: Feb 2008
Posts: 1,272
Mein Auto: '03 525i
You would need pretty much everything from that 330 6-speed car from the flywheel back, save keeping your differential: https://www.e46fanatics.com/threads/...d-swap.892869/
__________________
'12 328i Cab Deep Sea Blu/Tan
'03 525i Sapphire Blu/Grey, SP, Nav
'03 530i Sterling Gray/Blk, SP
'02 325it Orient Blu/Grey, SP, Nav
Reply With Quote
  #16  
Old 07-07-2020, 08:59 AM
Zeichen311's Avatar
Zeichen311 Zeichen311 is online now
Lost but making good time
Location: Here, there, or in transit
 
Join Date: Mar 2011
Posts: 5,400
Mein Auto: '11 335xi 4dr; '03 330Ci
The least expensive and simplest option, honestly, is to just get used to the fact that the 330i's drivetrain is a completely different beast from your old Corolla (per your flywheel thread). It likes humming along at 3000 rpm, all day long, and will return close to 30 mpg while doing so.

Granted, this may be no small adjustment if one is accustomed to grocery-getters that trundle down the highway at 2000 rpm or less in top gear. The payoff, though, is that you are sitting right in the meat of the torque band while cruising @ 75-80mph--mat the pedal and it will accelerate smartly even without a downshift. Clever gearing like that is, as Bob alluded earlier, a huge part of what enables BMWs to "punch above their weight class" for relatively mild (by performance-car standards) power output. At 3200rpm the engine is not straining at all.

It's variation of the "learn to love what ya got" philosophy often cited here. The six-speed is certainly a nice upgrade but it's not a small investment if you can't do the work yourself.
__________________
2011 335xi Individual 6MT - Azurite Black Metallic / Oyster & Black / Anthracite Maple + all the good stuff
2003 330Ci Sport 5MT - Black Sapphire Metallic / Natural Brown / Myrtle + the important stuff (+ go-fast stuff)

BMW CCA
Reply With Quote
  #17  
Old 07-07-2020, 10:13 AM
meinbills meinbills is offline
Officially Welcomed to the 'Fest
Location: Wisconsin
 
Join Date: May 2017
Posts: 778
Mein Auto: 2001 325ci/2003 330i
Agree but it is nice to have that 6th slot if I want to use it (and I definitely will on the freeway). Fortunately there is plenty of utoobe vids out there that I can refer to. Unfortunately it's the $ (if my wife sees another big box for auto part coming home containing the trans, she'd flip) and the lack of free time. Even though it seems I have had a lot of parts delivered for my 330 and it hasn't gone unnoticed by the wife, I checked and my expense so far is about $500, include the most expensive item, the fuel pump. Not so bad for a toy that put a smile on my face this morning, literally, as I got out of the car and walk into the grocery store.
Reply With Quote
  #18  
Old 07-07-2020, 01:31 PM
Fast Bob's Avatar
Fast Bob Fast Bob is online now
Keeping it surreal
Location: Here, there, everywhere....
 
Join Date: Jun 2004
Posts: 42,951
Mein Auto: 2004 330Ci ZHP 3 pedals
Quote:
Originally Posted by meinbills View Post
Agree but it is nice to have that 6th slot if I want to use it (and I definitely will on the freeway). Fortunately there is plenty of utoobe vids out there that I can refer to. Unfortunately it's the $ (if my wife sees another big box for auto part coming home containing the trans, she'd flip) and the lack of free time. Even though it seems I have had a lot of parts delivered for my 330 and it hasn't gone unnoticed by the wife, I checked and my expense so far is about $500, include the most expensive item, the fuel pump. Not so bad for a toy that put a smile on my face this morning, literally, as I got out of the car and walk into the grocery store.
Or, sell off all your non-essential stuff, and just buy yourself a nice ZHP (!), which comes in several flavors....Coupe. Sedan, or ragtop. Just think....6-speed, more power, better handling....Hell, it might even make a better driver out of you !
__________________
The road goes ever onward....
(R.I.P. Jever)

*Please support the Disabled American Veterans*

When faced with choosing between two evils, always go with the one you`ve never tried before....
Reply With Quote
  #19  
Old 07-07-2020, 02:56 PM
meinbills meinbills is offline
Officially Welcomed to the 'Fest
Location: Wisconsin
 
Join Date: May 2017
Posts: 778
Mein Auto: 2001 325ci/2003 330i
I did contemplate about selling this 330i and getting another 330i but with a 6-speed this time. Funny how the test drive in which I took it to the freeway going 80 mph didn't bother me about the high RPM. Must have been too focus to listen for funny noises and didn't notice that. The high RPM is bearable but the emphasis is "bearable". However, not sure I want to go through the process of buying another used 330i and replacing a bunch of stuffs AGAIN so soon, now that I have my car all good. Also not sure I will be able to find a nice specimen. I watched some utoob vid about this one guy's experience of driving a 5-speed after a swap. In the comment section, someone asked how much he would charge to do a swap and he replied "$3700 for a 5-speed and $4500 for a 6-speed". I bought my car for $3700!!! The entire car!

Nuts.
Reply With Quote
  #20  
Old 07-08-2020, 04:22 AM
SPDSKTR SPDSKTR is offline
I'm a DlCK! So what?
Location: Birmingham, AL, USA
 
Join Date: Sep 2011
Posts: 3,584
Mein Auto: E46 ZHP TS2+ Coupe
I'll sell you my ZHP.
Reply With Quote
  #21  
Old 07-08-2020, 04:24 AM
u.nanimous u.nanimous is offline
Certifiable BMW Whackjob!
Location: SE Michigan
 
Join Date: Oct 2014
Posts: 5,536
Mein Auto: 1999 740iS, 2008 335xi
The car has depreciated big time, used parts just a little bit, but labor follows inflation.

Posted through Tapatalk downloaded to my neural implant
__________________


2005 Venture Extended LT - what else you gonna drive when you have 6 kids, cargo and still want better than 10MPG
1999 740iA - long term project/summer DD
2000 Impala LS - RIP 12/23/2016, officially totaled by insurance company
2001 330xiA - fXtXeX/son project - now April's car
2008 335xiA - winterbeater Impala replacement
2002 530i/5 - 2.5 years searching...and it is John's car
1989 535i/5 - the spare car
2002 325xiA - to be Charlotte's when she gets her license (?2019?)
Reply With Quote
  #22  
Old 07-08-2020, 04:25 AM
u.nanimous u.nanimous is offline
Certifiable BMW Whackjob!
Location: SE Michigan
 
Join Date: Oct 2014
Posts: 5,536
Mein Auto: 1999 740iS, 2008 335xi
Quote:
Originally Posted by SPDSKTR View Post
I'll sell you my ZHP.
Nobody has snatched that up yet?

Posted through Tapatalk downloaded to my neural implant
__________________


2005 Venture Extended LT - what else you gonna drive when you have 6 kids, cargo and still want better than 10MPG
1999 740iA - long term project/summer DD
2000 Impala LS - RIP 12/23/2016, officially totaled by insurance company
2001 330xiA - fXtXeX/son project - now April's car
2008 335xiA - winterbeater Impala replacement
2002 530i/5 - 2.5 years searching...and it is John's car
1989 535i/5 - the spare car
2002 325xiA - to be Charlotte's when she gets her license (?2019?)
Reply With Quote
  #23  
Old 07-08-2020, 06:57 AM
meinbills meinbills is offline
Officially Welcomed to the 'Fest
Location: Wisconsin
 
Join Date: May 2017
Posts: 778
Mein Auto: 2001 325ci/2003 330i
Quote:
Originally Posted by SPDSKTR View Post
I'll sell you my ZHP.
I'm pretty sure you keep yours in tip top shape and it has all the goodies. Not sure I can afford it and plus it might not suit my lazy driving style.
Reply With Quote
  #24  
Old 07-08-2020, 06:59 AM
meinbills meinbills is offline
Officially Welcomed to the 'Fest
Location: Wisconsin
 
Join Date: May 2017
Posts: 778
Mein Auto: 2001 325ci/2003 330i
Quote:
Originally Posted by u.nanimous View Post
The car has depreciated big time, used parts just a little bit, but labor follows inflation.

Posted through Tapatalk downloaded to my neural implant
That's the reason why I bought another e46 because I'm familiar with working on it. If I couldn't do the work myself, then I am not sure I would even have kept the 325Ci, let alone buying the 330i
Reply With Quote
  #25  
Old 07-08-2020, 07:37 AM
SPDSKTR SPDSKTR is offline
I'm a DlCK! So what?
Location: Birmingham, AL, USA
 
Join Date: Sep 2011
Posts: 3,584
Mein Auto: E46 ZHP TS2+ Coupe
Quote:
Originally Posted by u.nanimous View Post
Nobody has snatched that up yet?

Posted through Tapatalk downloaded to my neural implant
I'm not pushing it as hard as I should. It's hard to let that car go. I'm the second owner and it's set up so, so perfectly, harsh ride be damned. I gotta accept the fact it's time to grow up a bit and get something better in the future.

Quote:
Originally Posted by meinbills View Post
I'm pretty sure you keep yours in tip top shape and it has all the goodies. Not sure I can afford it and plus it might not suit my lazy driving style.
It's definitely not a "lazy" car.
Reply With Quote
Reply

See More Related BMW Stories


Forum Navigation
Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 3 Series & 4 Series > E46 (1999 - 2006)
Today's Posts Search
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On



Forum Jump


All times are GMT -7. The time now is 09:37 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
© 2001- VerticalScope Inc. All rights reserved.