Results 1 to 20 of 20

Thread: Swapping to Shorter Diff Ratio - Regrets?

  1. #1
    Join Date
    Feb 2016
    Location
    Philadelphia
    Posts
    119
    My Cars
    2001 BMW M Roadster

    Swapping to Shorter Diff Ratio - Regrets?

    Hi all,

    I seldom post on here (been over a year at least). But after extensive research on these forums and the web in general, I decided about 2 years ago after having owned my 01 M Roady for about 1 year to install a 3.64 Torsen diff from a 01 Z3 2.5i auto. My goal was to be able to utilize the full rev range since the S54 loves to rev and makes most of its power above 4,900 rpms all the way to redline (7,800 in my case after custom tune). I thought being in the peak power band more often would make the car feel more awake and even more fun to drive (and that's all I read about). This is a weekend toy for me, driven on the street (never tracked), driven about 3k miles/year in optimal weather conditions only. However, after having put about 5-6k miles on it since the 3.64 diff install, I'm having second thoughts about the swap. Sure, it revs way faster in each gear and feels like it has way more grunt down low, but I kinda miss the way it used to rev forever it seemed (of course, due to the longer final drive more so than the high redline I've now come to realize). It used to be a highway monster. Now, it's a dragster! Great from digs (although I never launch it for the sake of saving my clutch). But from rolls, say 30 or 40mph on, it doesn't have the same pull (feel) it did before IMO. Makes sense the more reading I do on this. Plenty of threads out there discussing how putting in a shorter diff is beneficial and will make the car feel way faster (by accelerating quicker in each gear), and is a big torque multiplier, but I think the shorter diff is best suited for people who care about 1/4 mile times. For street driving, even spirited driving, I almost think the taller, 3.15 ratio diff is better suited for this car. By shortening the gears, I feel like it actually doesn't feel as fierce in the upper rev range. I understand the engine doesn't actually lose hp or gain tq spec-wise, but it certainly FEELS like it did. Makes sense considering it does have more torque down low, but the offset is lost hp feel up high. My daily driver is a 18 VW GTI with a tune, so I'm making over 300 lb/ft torque in that little monster (best daily driver IMO... and can be bought for a steal right now with heavy discounts). The thing I love about the Z3M (specifically with the S54) is how the power keeps building all the way up to redline. With the shorter diff, I feel I've lost that upper rev range rush it had before. I feel like any car that doesn't make power up high would benefit from the shorter diff since 1st and 2nd rev out so quick anyway, the high hp nature of the S54 above 5k rpms is kinda lost. Do others who've switched feel the same? Or am I alone? I still have my stock 3.15 diff and am considering reinstalling it and selling the 3.64. It'll be a wash between the sale of the 3.64 and having my mechanic install the old one monetary wise, so that doesn't matter much to me. Plus, I must say revving at almost 4k at 80mph on the highway gets kinda annoying too LOL. Otherwise, the car is perfect and I love that finally the roadsters are getting more appreciation recently (check BaT for proof in that regard). These manual, high strung, driver's cars will never be built again (sadly). These cars deserve just as much praise as an S2000.
    2001 BMW M Roadster - Steel Gray over Imola Red/Black (1 of 8), Eisenmann sport exhaust, KW V3 coilovers, Strong Strut engine brace, Randy Forbes subframe reinforcement, GSR Technik tune, 3.64 Torsen LSD...Weekend toy!
    ">

  2. #2
    Join Date
    Oct 2008
    Location
    SFBay, CA
    Posts
    309
    My Cars
    02 LSB Z3M Coupe
    Maybe a 3.46 would be a happy medium?
    I installed a 3.46 into my S52 and it's the best modification I've made by far. It would be a must-have if I ever bought an S54.
    You could also try a 3.23 from an S52 car, which would offer a bit more ability to rev, but it might not be too noticeable compared to the 3.15.

  3. #3
    Join Date
    Jan 2008
    Location
    Arida Zona
    Posts
    30,107
    My Cars
    z3
    Id be interested if you decide to sell the 3.64

    My s54 has a 6 speed so theres no compromise for me. I have a 3.73 here ready to go in but would prefer a 3.64

    Personally I think the s54 feels like a dog with the 3.15, I have an S52 M3 that feels faster

    Going into my TENTH YEAR of providing high quality reproduction BMW fabrics!

    PRICE CUT on ALL FABRICS
    Offering the best prices on the best quality reproduction fabrics!

  4. #4
    Join Date
    Jan 2004
    Location
    Bay Area, Killa Kali
    Posts
    8,312
    My Cars
    2002 M Coupe, 2019 F31
    I also agree that the 3.15 did not feel like the proper ratio for the S54.

    3.46 with the stock 5-speed was perfect for me and said ratio came out of the automatic Z3 3.0 variant.
    Last edited by CaliAgents; 04-18-2019 at 01:01 PM.

    -2023 Honda Odyssey Elite
    -2019 F31 Individual (M-Sport, Prem, Exec, Track)
    -2004 Honda CRV
    -2002 S54 M Coupé

  5. #5
    Join Date
    Feb 2016
    Location
    Philadelphia
    Posts
    119
    My Cars
    2001 BMW M Roadster
    Quote Originally Posted by CaliAgents View Post
    I also agree that the 3.15 did not feel like the proper ratio for the S54.

    3.46 with the stock 5-speed was perfect for me. The 3.46 came out of the automatic Z3 3.0 variant.
    Are you on stock wheels/tires?
    2001 BMW M Roadster - Steel Gray over Imola Red/Black (1 of 8), Eisenmann sport exhaust, KW V3 coilovers, Strong Strut engine brace, Randy Forbes subframe reinforcement, GSR Technik tune, 3.64 Torsen LSD...Weekend toy!
    ">

  6. #6
    Join Date
    Jan 2004
    Location
    Bay Area, Killa Kali
    Posts
    8,312
    My Cars
    2002 M Coupe, 2019 F31
    No, I am on 18x9s and 18x11 Apex wheels with 245/35 and 295/30 sized tires.

    It was more dramatic for me as I had heavy 19s when I installed the 3.46. Even when the car was stock, I felt like a shorter ratio diff would make it even more fun. From what I recall BMW purposely used a taller final drive to handicap it a bit so it wouldn't best the flagship M3.
    Last edited by CaliAgents; 04-18-2019 at 01:46 PM.

    -2023 Honda Odyssey Elite
    -2019 F31 Individual (M-Sport, Prem, Exec, Track)
    -2004 Honda CRV
    -2002 S54 M Coupé

  7. #7
    Join Date
    Feb 2016
    Location
    Philadelphia
    Posts
    119
    My Cars
    2001 BMW M Roadster
    Quote Originally Posted by CaliAgents View Post
    No, I am on 18x9s and 18x11 Apex wheels with 245/35 and 295/30 sized tires.

    It was more dramatic for me as I had heavy 19s when I installed the 3.46. Even when the car was stock, I felt like a shorter ratio diff would make it even more fun. From what I recall BMW purposely used a taller final drive to handicap it a bit so it wouldn't best the flagship M3.
    With your bigger size wheels, I'm guessing it feels closer to one with stock wheels and the 3.15 final drive.

    I don't know if anyone knows for sure (just speculation) when it comes to why BMW outfitted the S54 with the 3.15 diff versus a 3.46, 3.64, or 3.73. The 5 speed being the biggest factor, IMO, for why they chose to stick with the tall final driver (reasonable cruising RPM in 5th). They would have needed to put in a 6-speed, and obviously they weren't going to waste the money towards R&D to put that in at the tail end of Z3 production with the Z4 unveiling around the corner. I honestly think the 3.15 might be better still for the S54. Even the E46 M3 has a 3.64 diff if I'm not mistaken, but rides on bigger 18 or 19" wheels, again, offsetting the shorter diff. They're over 100mph in 3rd gear at redline just like the Z3M (my former max speed saw almost 110mph in 3rd, now I'm around 95mph or so).

    Only way I'll know for sure is when I meet up with this local guy to me to compare. I don't know a single person with a Z3M, much less an S54 equipped one! Hopefully meeting with him soon. I know this is all preference, but I'm curious to do back-to-back comparisons with his car and mine. I care more about "feel" than the fact I may be shaving .1 seconds off the 1/4 mile with the shorter diff.
    2001 BMW M Roadster - Steel Gray over Imola Red/Black (1 of 8), Eisenmann sport exhaust, KW V3 coilovers, Strong Strut engine brace, Randy Forbes subframe reinforcement, GSR Technik tune, 3.64 Torsen LSD...Weekend toy!
    ">

  8. #8
    Join Date
    Jan 2011
    Location
    Kent, Ohio
    Posts
    4,431
    My Cars
    1998 M Roadster
    OP, I think that in order to make that swap to a 3.64 or a 3.73 really make sense across the full spectrum (and especially on the highway), you have to pair it with a 6 speed. There's a reason the ///M division installed a 3.15, and it wasn't because they had extra lying around or couldn't do math. I have a supercharged S52 with the original diff, and it's a monster puller on the highway in 4th and 5th--after about 4k it just seems to keep growing exponentially until redline (or I run out of nerve in 5th). I seriously contemplated a 3.64 and 6 speed, but like you, I really don't care about the 1/4 mile. No matter what I do it's not going to compete with modern muscle (or even diesel pickups) from a start--it's up high and in the twists and turns that I really enjoy the power. I'm not suggesting my supercharged S52 compares with an S54 mind you, but I get where you're coming from in contemplating going back. Besides, I have a Viper for that if I really feel like it (and I rarely do).

  9. #9
    Join Date
    Jan 2008
    Location
    Arida Zona
    Posts
    30,107
    My Cars
    z3
    If BMW wasn't limiting the M coupe's ability with the diff, why did they switch from a 3.23 with the lower-revving S52 to a 3.15 when they went to the high revving S54? The transmissions are the same so all the other ratios are identical. The S54 would definitely not have been hurting from a 3.23 at the bare minimum. Sure they didn't want to switch to a 6 speed in the Z3M but I don't think there is any logical explanation for the ratio change. There is also other evidence they limited the Z3M from the factory... the cars have sport mode enabled on the DME, even a spot for a "sport mode" to illuminate on the cluster, the throttle response changes are programmed in and everything but they just never installed a button for it. It is believed, and I agree, that the //Marketing team was afraid of the outgoing Z3 stepping on the new M3's toes so they limited it a bit. The Z3M S54 also makes a bit less power than the E46 M3.

    I haven't done the diff swap on this car but on my other cars it just shifted where it felt the powerband was. Sure it may not be a slingshot onto the highway in 3rd gear anymore, but it should rip through the gears just about everywhere else. Maybe a 3.46 would be better with the 5 speed or a 3.23 as a "no sacrifice" compromise (if an S52 can turn at whatever RPM it turns on a highway with a 3.23, so can an S54).

    Going into my TENTH YEAR of providing high quality reproduction BMW fabrics!

    PRICE CUT on ALL FABRICS
    Offering the best prices on the best quality reproduction fabrics!

  10. #10
    Join Date
    Feb 2014
    Location
    Galt,CA
    Posts
    1,068
    My Cars
    2002 M Coupe
    Quote Originally Posted by BimmerBreaker View Post
    If BMW wasn't limiting the M coupe's ability with the diff, why did they switch from a 3.23 with the lower-revving S52 to a 3.15 when they went to the high revving S54? The transmissions are the same so all the other ratios are identical. The S54 would definitely not have been hurting from a 3.23 at the bare minimum. Sure they didn't want to switch to a 6 speed in the Z3M but I don't think there is any logical explanation for the ratio change. There is also other evidence they limited the Z3M from the factory... the cars have sport mode enabled on the DME, even a spot for a "sport mode" to illuminate on the cluster, the throttle response changes are programmed in and everything but they just never installed a button for it. It is believed, and I agree, that the //Marketing team was afraid of the outgoing Z3 stepping on the new M3's toes so they limited it a bit. The Z3M S54 also makes a bit less power than the E46 M3.

    I haven't done the diff swap on this car but on my other cars it just shifted where it felt the powerband was. Sure it may not be a slingshot onto the highway in 3rd gear anymore, but it should rip through the gears just about everywhere else. Maybe a 3.46 would be better with the 5 speed or a 3.23 as a "no sacrifice" compromise (if an S52 can turn at whatever RPM it turns on a highway with a 3.23, so can an S54).
    You're overlooking that fact that the dyno sheets posted by no less than Randy Forbes prove that the S54 had more torque at every RPM than the S52 has. So the slightly higher gear ratio does not hinder the acceleration, but does give it a monster top end. The only third party road test of an S54 Coupe I've ever seen had them clocking their example at 160 MPH, which is only around 6000 RPM. For my street use the 3.15 works just fine.

    Marty

  11. #11
    Join Date
    Jan 2011
    Location
    Kent, Ohio
    Posts
    4,431
    My Cars
    1998 M Roadster
    Quote Originally Posted by BimmerBreaker View Post
    If BMW wasn't limiting the M coupe's ability with the diff, why did they switch from a 3.23 with the lower-revving S52 to a 3.15 when they went to the high revving S54? The transmissions are the same so all the other ratios are identical. The S54 would definitely not have been hurting from a 3.23 at the bare minimum. Sure they didn't want to switch to a 6 speed in the Z3M but I don't think there is any logical explanation for the ratio change. There is also other evidence they limited the Z3M from the factory... the cars have sport mode enabled on the DME, even a spot for a "sport mode" to illuminate on the cluster, the throttle response changes are programmed in and everything but they just never installed a button for it. It is believed, and I agree, that the //Marketing team was afraid of the outgoing Z3 stepping on the new M3's toes so they limited it a bit. The Z3M S54 also makes a bit less power than the E46 M3.

    I haven't done the diff swap on this car but on my other cars it just shifted where it felt the powerband was. Sure it may not be a slingshot onto the highway in 3rd gear anymore, but it should rip through the gears just about everywhere else. Maybe a 3.46 would be better with the 5 speed or a 3.23 as a "no sacrifice" compromise (if an S52 can turn at whatever RPM it turns on a highway with a 3.23, so can an S54).
    I think they must have gone down in ratio to take advantage of the higher redline for top end, but I agree that BMW de-tuned the S54 MZ3's to avoid competing with the M3.

  12. #12
    Join Date
    Sep 2018
    Location
    SoCal
    Posts
    17
    My Cars
    2002 BMW Z3 M Coupe
    I am running a clutch type 3.46 from a old school 6 series. Perfect medium and mpg is fine in fact better somehow. My car is a 2002 S54 M coupe— tires are 18x8.5 and 18x10 245/35 and 285/30
    Last edited by mercedesc63; 04-18-2019 at 10:26 PM.

  13. #13
    Join Date
    May 2009
    Location
    Richmond, VA
    Posts
    704
    My Cars
    Spec3 & MCoupe
    Quote Originally Posted by spikeisgr8 View Post
    I still have my stock 3.15 diff and am considering reinstalling it and selling the 3.64. It'll be a wash between the sale of the 3.64 and having my mechanic install the old one monetary wise, so that doesn't matter much to me.
    If you decide you want to put the 3.15 diff back in, I'd be interested in coming up to PA, swapping the diffs for you, and purchasing the 3.64. That'd be pretty easy to knock out in an afternoon. I grew up in Doylestown, PA so I can definitely find a garage to work in if you don't have a place to do the work. My S52 Coupe wants a 6-speed and a poor man's supercharger!

  14. #14
    Join Date
    Feb 2006
    Location
    Tim @ BMW of Dallas
    Posts
    1,889
    My Cars
    98 Z3 2.8
    I've always thought the S54 cars felt sluggish with the 3.15 ratio. Although I've never had a chance to drive one with a "proper" ratio, I've swapped from a 3.15 to a 3.46 on both of my lowly 2.8's and it's by far one of my favorite things I've done. I think an S54 car with a 3.46 or 3.64 and a 6-speed swap would be phenomenal.
    96 320i Touring
    98 Z3 2.8 Roadster
    01 PY M Coupe
    96 Z3 1.9 - DASC
    95 318ti Clubsport
    94 Miata M-Edition
    13 smart fortwo



  15. #15
    Join Date
    Feb 2004
    Location
    VA
    Posts
    727
    My Cars
    N/A
    3.46 seems ideal of the stock diffs. Had 3.73 and it's a bit much. 3.15 feels fine to me unless you really want more pep.

    If I had to make up a ratio for the 5spd, I'd say 3.30-3.35 or something like that would be perfect.

  16. #16
    Join Date
    Sep 2018
    Location
    SoCal
    Posts
    17
    My Cars
    2002 BMW Z3 M Coupe
    Quote Originally Posted by workhurts View Post
    3.46 seems ideal of the stock diffs. Had 3.73 and it's a bit much. 3.15 feels fine to me unless you really want more pep.

    If I had to make up a ratio for the 5spd, I'd say 3.30-3.35 or something like that would be perfect.
    As an owner of a 3.46 I also dream of the perfect ratio for me the perfect is like 3.50-3.55 with 3 clutches and upgded ramp angles 60/40 lockup.

  17. #17
    Join Date
    May 2002
    Location
    SW Florida
    Posts
    12,681
    My Cars
    99-01 M Cpe & Rdts, X5M
    I put a 3.73:1 (40% l/u) in my '01 M Rdstr when it was just a few months old. I drive A LOT of other people's cars__talking S54 M Coupes/Rdstrs__and when I get in one with a stock ratio, it feels like I'm dragging an anchor.

    I never felt that mine was revving too high on the freeway, and had often found that a few miles down the road, after merging and settling into the traffic flow, I'd not yet shifted up from 4th to 5th (interestingly, in my S52, NUMEROUS TIMES under the same circumstances, I'd reflexively shifted out of 5th towards a nonexistent 6th gear!).

    If the original poster elects to swap back to the 3.15:1 ratio, my recommendation is to NOT SELL the 3.64:1 right away. Give yourself time to evaluate the new__original__driving characteristics, because your impressions are the polar opposite of mine.

  18. #18
    Join Date
    Feb 2016
    Location
    Philadelphia
    Posts
    119
    My Cars
    2001 BMW M Roadster
    Quote Originally Posted by Randy Forbes View Post
    If the original poster elects to swap back to the 3.15:1 ratio, my recommendation is to NOT SELL the 3.64:1 right away. Give yourself time to evaluate the new__original__driving characteristics, because your impressions are the polar opposite of mine.
    Think of it less as I can't sense the thrilling urgency in which the engine responds now as a result of the shorter ratio diff, but more so that I think I enjoy the "long legs" feel a taller diff provides. The high 7,400 rpm peak power makes the car feel like it pulls and pulls and pulls all the way to redline strong. With the shorter diff, in 1st and 2nd now for example, the "pulling" feel goes by quicker because you accelerate much quicker in each gear. So in a sense, the top end pull feels less significant because the gears fly by so fast anyway. It makes it feel like the strong top end is less significant. Almost as if the car could theoretically have a less high strung, high peak hp engine and still feel similarly as fast (particularly gears 1 and 2, maybe 3 as well). The thrill, to me, of the S54 is the high strung top end nature of the motor. It hates being driven below 3-4,000 rpm. The shorter diff helps with that (being up more rpm in any given gear) but the faster acceleration in each girl might not transfer to the butt dyno the feeling I was hoping for. Sure, it has more torque down low. But I hate driving the car below 3k rpm unless I'm cruising, and I usually don't punch it unless I'm on an optimal road and when near peak torque. The rush feels more powerful from 5k to 7,600. Again, for a street driven car, not auto-xing, I think the taller ratio provides a more fun and comfortable mix feeling that is favorable in most driving conditions (especially when highway driven sometimes, or just anytime over 65mph).

    I won't be making any changes until I meet up with this local friend who has the same spec car as mine (albeit totally stock). I will definitely be interested in seeing how his drives versus mine. I've only run into 3 people with Z3M's in 3 plus years now. Rare and hard to come by!
    2001 BMW M Roadster - Steel Gray over Imola Red/Black (1 of 8), Eisenmann sport exhaust, KW V3 coilovers, Strong Strut engine brace, Randy Forbes subframe reinforcement, GSR Technik tune, 3.64 Torsen LSD...Weekend toy!
    ">

  19. #19
    Join Date
    Sep 2017
    Location
    Summerfield, NC
    Posts
    4
    My Cars
    1998 Z3
    I have a 3.15 in my 1998 z3 track car and I am looking for a 3.73 or similar. Want to swap?

  20. #20
    Join Date
    Feb 2016
    Location
    Philadelphia
    Posts
    119
    My Cars
    2001 BMW M Roadster
    Quote Originally Posted by VetteDude View Post
    I have a 3.15 in my 1998 z3 track car and I am looking for a 3.73 or similar. Want to swap?
    Appreciate the offer. Still have my original 3.15 diff laying around if I decide to switch back.
    2001 BMW M Roadster - Steel Gray over Imola Red/Black (1 of 8), Eisenmann sport exhaust, KW V3 coilovers, Strong Strut engine brace, Randy Forbes subframe reinforcement, GSR Technik tune, 3.64 Torsen LSD...Weekend toy!
    ">

Similar Threads

  1. E36 BMW Motorsport M3 E36(only 3.2l) shorter rear diff ratio 3,62
    By Markus in forum Drivetrain & Transmission Parts
    Replies: 1
    Last Post: 08-14-2011, 04:56 AM
  2. E36 BMW Motorsport M3 E36(only 3.2l) shorter rear diff ratio 3,62
    By Markus in forum Drivetrain & Transmission Parts
    Replies: 0
    Last Post: 08-11-2011, 11:46 AM
  3. Question about swapping diff ratios or lsd units.
    By Jon Mar in forum 1988 - 1996 (E34)
    Replies: 11
    Last Post: 12-01-2009, 03:33 PM
  4. zf310/5 swap complete! Diff ratio question- everyone applys
    By Dinglenutz in forum 1988 - 1996 (E34)
    Replies: 6
    Last Post: 06-11-2009, 04:31 PM
  5. Replies: 17
    Last Post: 12-20-2004, 06:25 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •