3.91 in an E39 M5 - BMW M5 Forum and M6 Forums
E39 M5 and E52 Z8 Discussion 1998-2003 Advertiser's Forum

 17Likes
Reply
 
LinkBack Thread Tools Rate Thread Display Modes
post #1 of 18 Old 10th December 2017, 08:14 AM Thread Starter
Black ///M10
Member, Sport: Off DSC: On (>50 posts)
 
Black ///M10's Avatar
 
Join Date: Jan 2013
Location: Sunland, CA
Posts: 61
Thanks: 1
Thanked 3 Times in 2 Posts
3.91 in an E39 M5

Yup, another differential ratio question.

I am considering going with 3.62 or 3.64 gears on my M5. However, I want to see if anyone has ever done 3.91 on an E39 M5. I searched all over the forum. The only 3.91 inquiries are related to E60 M5's, so Im creating this thread to get some feedback from anyone who has done it before or some experienced board members who can give some more information.

Arty

Current Garage:
78k mile Garage-Queen 1999 Turbo M3 [585whp/608wtq]
2002 Bluewater M5 [Dinan S1]
2001 Imola Red M5
INTERIOR
Black/Imola Red Interior
Mark IV Navi Upgrade
Dice IPOD Integration
Alcantara Shift and Ebrake Boot
ENGINE
Evolve Alpha N Tune
IATS Relocation
AFE Dry Element Drop Ins
DRIVETRAIN
Dinan Front Strut Bar
Dinan Rear Swaybar
Dinan Springs & Koni Sports
Rogue SSK & Trans Mounts
Brake Ducts
FORMER
'98 Estoril Blue M3
'96 SC'd Techno Violet M3
'02 Carbon Black M5 [Dinan S2]
'06 Interlagos Blue E60 M5 [21" 3 pc. Hartge wheels]
'97 RB25det 240sx [485 whp]
'17 Audi A6,
'99 Evergreen M Roadster
Black ///M10 is offline  
Sponsored Links
Advertisement
 
post #2 of 18 Old 10th December 2017, 01:38 PM
Ferris
m5board.comoholic (>1000 posts)
 
Join Date: Dec 2012
Location: New Jersey
Posts: 1,326
Thanks: 4
Thanked 129 Times in 118 Posts
Going to ask the dumb question here, why? The S62 puts out a ton of torque in my opinion.

2001 E36/7 MRoadster
2001 E39 M5
2010 E60 M5
2008 E90 335xi
Ferris is offline  
post #3 of 18 Old 10th December 2017, 02:01 PM
herrubermensch
M5 Expert (>4000)
 
Join Date: Aug 2008
Location: New York
Age: 53
Posts: 8,708
Thanks: 4,472
Thanked 2,607 Times in 1,548 Posts
Quote:
Originally Posted by Ferris View Post
Going to ask the dumb question here, why? The S62 puts out a ton of torque in my opinion.
The principal reason is to keep the S62 in the ideal RPM range, thereby maximizing its output, for the application. So for example, if the engine is set up to maximize power output in the 5-7k rpm range, shorter gears help to keep the engine in that range.

To be sure, this is more of a track-oriented analysis. If your goal is to be quick off the line, I agree, shorter gears are going to be tough to use with an S62 absent some serious additional meat in the rear. From a 30-40 mph roll, however, they can be delightful.

--Peter
herrubermensch is offline  
 
post #4 of 18 Old 10th December 2017, 05:06 PM
gzig5
m5board.comoholic (>1000 posts)
 
Join Date: Dec 2008
Location: Mequon, WI
Posts: 1,853
Thanks: 95
Thanked 319 Times in 238 Posts
On the street and maybe the dragstrip, I'd have to imagine that 3.91's would make 1st gear essentially useless. I've got 3.45 and that first shift comes awful quick when you give it the beans. I use second gear a lot in stop and go traffic or gentle acceleration from stop signs in the village. You will need some sticky tires or you'll just be blowing them off. I agree with Peter regarding road track use though.

_____________
2000 M5 Carbon Black
Dinan 3.45 Differential
Evolve Tune
Dinan Springs w/ Koni Yellow Sport shocks
Dinan Rear Sway Bar
E60 545 SSK
275 PSS on OEM 9.5" all around
Home-built Muffler Delete
gzig5 is offline  
post #5 of 18 Old 10th December 2017, 06:17 PM
Eurosapien
Member, Sport: On DSC: On (>100 posts)
 
Eurosapien's Avatar
 
Join Date: Sep 2015
Location: San Diego, CA
Posts: 159
Thanks: 3
Thanked 7 Times in 7 Posts
Eurosapien is offline  
post #6 of 18 Old 10th December 2017, 09:59 PM Thread Starter
Black ///M10
Member, Sport: Off DSC: On (>50 posts)
 
Black ///M10's Avatar
 
Join Date: Jan 2013
Location: Sunland, CA
Posts: 61
Thanks: 1
Thanked 3 Times in 2 Posts
After further research, I've decided to go with a 3.62. That'll give the car a noticeable difference on the butt-dyno while the RPM's at highway speeds in 6th gear will stay relatively low. My main concern was to not lose the 6th gear cruising comfort.

I used the RPM calculator on ringpinion.com:
-6th gear, 75mph = 2947 RPM
-6th gear, 85mph = 3340 RPM
-6th gear, 100mph = 3929 RPM

I'll also be able to feel a nice difference in 1st and 2nd. I rarely rip through 1st or 2nd gear to begin with, so I'm okay with losing a little traction when I do give it a nice pull in the rare occasion. I've got a turbo E36 M3 with 608wtq and 585whp. It loses traction in 3rd gear. Sometimes when I get into the E39 after driving the M3 for a few days, it feels odd having half the amount of torque in a V8... So I feel like the 3.62 will give me what I want without being too much and defeating its character as a luxury sport sedan.

Here are some videos I found of E39 M5's with the 3.62:

https://www.youtube.com/watch?v=6gP_w5DWjFQ

https://www.youtube.com/watch?v=i2kC0X3SghQ

https://www.youtube.com/watch?v=tzz2soTaOD8 (this one's got a 3.64)

Arty

Current Garage:
78k mile Garage-Queen 1999 Turbo M3 [585whp/608wtq]
2002 Bluewater M5 [Dinan S1]
2001 Imola Red M5
INTERIOR
Black/Imola Red Interior
Mark IV Navi Upgrade
Dice IPOD Integration
Alcantara Shift and Ebrake Boot
ENGINE
Evolve Alpha N Tune
IATS Relocation
AFE Dry Element Drop Ins
DRIVETRAIN
Dinan Front Strut Bar
Dinan Rear Swaybar
Dinan Springs & Koni Sports
Rogue SSK & Trans Mounts
Brake Ducts
FORMER
'98 Estoril Blue M3
'96 SC'd Techno Violet M3
'02 Carbon Black M5 [Dinan S2]
'06 Interlagos Blue E60 M5 [21" 3 pc. Hartge wheels]
'97 RB25det 240sx [485 whp]
'17 Audi A6,
'99 Evergreen M Roadster
Black ///M10 is offline  
post #7 of 18 Old 11th December 2017, 04:03 AM
herrubermensch
M5 Expert (>4000)
 
Join Date: Aug 2008
Location: New York
Age: 53
Posts: 8,708
Thanks: 4,472
Thanked 2,607 Times in 1,548 Posts
Quote:
Originally Posted by Black ///M10 View Post
Sometimes when I get into the E39 after driving the M3 for a few days, it feels odd having half the amount of torque in a V8... So I feel like the 3.62 will give me what I want without being too much and defeating its character as a luxury sport sedan.
Throw a good supercharger setup on the S62, push 15 ppsi through it, and you'll have the same level of torque as the M3, and it will hit early and stay there--like a table top! And you won't defeat the car's character.

--Peter
herrubermensch is offline  
post #8 of 18 Old 11th December 2017, 04:46 AM
Eurosapien
Member, Sport: On DSC: On (>100 posts)
 
Eurosapien's Avatar
 
Join Date: Sep 2015
Location: San Diego, CA
Posts: 159
Thanks: 3
Thanked 7 Times in 7 Posts
Quote:
Originally Posted by herrubermensch View Post
Throw a good supercharger setup on the S62, push 15 ppsi through it, and you'll have the same level of torque as the M3, and it will hit early and stay there--like a table top! And you won't defeat the car's character.

--Peter
What kind of longevity would you expect out of our gearbox at 15 psi power levels?
Eurosapien is offline  
post #9 of 18 Old 11th December 2017, 08:37 AM Thread Starter
Black ///M10
Member, Sport: Off DSC: On (>50 posts)
 
Black ///M10's Avatar
 
Join Date: Jan 2013
Location: Sunland, CA
Posts: 61
Thanks: 1
Thanked 3 Times in 2 Posts
Quote:
Originally Posted by herrubermensch View Post
Throw a good supercharger setup on the S62, push 15 ppsi through it, and you'll have the same level of torque as the M3, and it will hit early and stay there--like a table top! And you won't defeat the car's character.

--Peter
That is certainly the plan one day, but not in the near future.

Arty

Current Garage:
78k mile Garage-Queen 1999 Turbo M3 [585whp/608wtq]
2002 Bluewater M5 [Dinan S1]
2001 Imola Red M5
INTERIOR
Black/Imola Red Interior
Mark IV Navi Upgrade
Dice IPOD Integration
Alcantara Shift and Ebrake Boot
ENGINE
Evolve Alpha N Tune
IATS Relocation
AFE Dry Element Drop Ins
DRIVETRAIN
Dinan Front Strut Bar
Dinan Rear Swaybar
Dinan Springs & Koni Sports
Rogue SSK & Trans Mounts
Brake Ducts
FORMER
'98 Estoril Blue M3
'96 SC'd Techno Violet M3
'02 Carbon Black M5 [Dinan S2]
'06 Interlagos Blue E60 M5 [21" 3 pc. Hartge wheels]
'97 RB25det 240sx [485 whp]
'17 Audi A6,
'99 Evergreen M Roadster

Last edited by Black ///M10; 11th December 2017 at 08:37 AM.
Black ///M10 is offline  
post #10 of 18 Old 11th December 2017, 01:41 PM
CSBM5
M5 Expert (>4000)
 
CSBM5's Avatar
 
Join Date: Aug 2002
Location: Raleigh, NC
Age: 60
Posts: 7,468
Thanks: 1,642
Thanked 1,505 Times in 1,029 Posts
In terms of outright acceleration performance, there will be essentially no gain, and depending on the speed increment evaluated, it will either be a slight loss (or significant loss if a now needed shift is in the middle of the increment) or a slight gain. When people use butt dynos, they feel the added torque to the wheels in some given gear (like 2nd) but fail to recognize the now reduced torque to the wheels once they shift to 3rd while the stock car would still be nailing the upper end of 2nd hard. It's a give and take trade-off. I did many sim runs 10+ years ago on the board with different rear end ratios, and they ended up correlating well with real world experience of some who measured before and after data. It's buried deep in the board here someplace, but the xcel and cartest images might not still be available.

You really only need to fool with changing the rear gear if you do other engine work that moves the sweet spot of the rpm range higher up the rev scale -- say porting, cams, ported throttle bodies, headers, etc, and a raised redline. At that point it likely makes sense to alter the rear gear. However, if actual, measurable gains aren't the objective, the "feel" of the shorter rear gear is of course interesting.

Current stable:

2019 M2 Competition 6MT LBB, slicktop
2011.5 M3 sedan 6MT Silverstone, slicktop: Dinan front swaybar, Eibach rear swaybar, pins-out-max-camber-up-front, Dinan exhaust, Michelin PS4S, Apex EC-7 9.5/10.5x19
2007 328i wagon Silver/gray: Eibach 28mm front swaybar, E93 M3 rear swaybar, 219M M3 wheels, Michelin PSAS3+
1975 CanAm 125MX2: Stock, original owner
CSBM5 is offline  
The Following User Says Thank You to CSBM5 For This Useful Post:
gsfent (11th December 2017)
Reply

Bookmarks

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the BMW M5 Forum and M6 Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes Rate This Thread
Linear Mode Linear Mode
Rate This Thread:



Similar Threads
Thread Thread Starter Forum Replies Last Post
BMW E39 (all E39 & M5) aluminum Headlight adjuster repair kit Bimmerzone.com M5 E39 Group Buy Forum and Sponsor Discussion and Offerings 40 29th October 2018 11:35 PM
E39 OEM Hella Xenon Headlights, Angel Eyes, from E39 M5 $350.00 BuzzedHornet Parts / Other For Sale or Wanted 17 14th April 2016 12:36 AM
E39 Want to buy: E39 BMW Sun Shield, E39 Repair Manual and E39 Black Front Grill for Sale sandiegoe39 Parts / Other For Sale or Wanted 2 16th December 2010 12:48 AM
E39 OEM Hella Xenon Headlights, Angel Eyes, from E39 M5 $350.00 BuzzedHornet E39 M5 and E52 Z8 Discussion 1 26th October 2008 09:07 PM

Posting Rules  
You may post new threads
You may 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
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome