|
|
|
01-12-2017, 02:42 PM | #1 |
Private First Class
26
Rep 144
Posts |
Which Diff Ratio to go with?
Hi guys, after upgrading suspension parts, RSFB, shocks and springs, I'm looking to change the diff ratio for my car to have shorter gearing so to speak.
I have a 128i with 18x8.5 wheels all around, manual transmission, DISA intake and AA tune. The car stock has 3.23 ratio, my friend who is phenomenal with car stuff, told me to look at about 20% change in diff ratio. I ran across this thread in my search http://www.1addicts.com/forums/showthread.php?t=1193231 seems that most people on the forum were leaning towards the 3.46 ratio rather than the 3.73. What are your opinions for my usage as far as what diff to look into swapping with: Daily drive the car in LOS ANGELES (so freeway speeds rarely get to anything passed even 70) no track time and dont plan on doing much tracking or autocross. Most of my spirited driving is canyon driving. The reason why i was looking at doing this upgrade is because i feel that although first gear actually is just right or slightly too short, the rest of the gears, particularly 2nd, are very tall and doesn't have the car in the right power band for the type of driving that is usual. any recommendations and insight is greatly appreciated! also, any recommendations on what diff to swap with?? |
01-12-2017, 03:07 PM | #2 | |
Слава Украине!
2335
Rep 2,443
Posts |
Quote:
I would think a 3.73 would be quite similar.
__________________
|
|
Appreciate
0
|
01-12-2017, 04:08 PM | #3 | |
Private First Class
26
Rep 144
Posts |
Quote:
Do you have a recommendation for which diff to swap with? Im looking to make this as straightforward and direct swap as possible |
|
Appreciate
0
|
01-12-2017, 05:12 PM | #4 |
!
701
Rep 3,268
Posts
Drives: 2010 128i
Join Date: Feb 2010
Location: Anacortes, WA
|
I have a 3.73 and think it's awesome. Really woke the car up, and 1st is not at all too short. I can't even imagine how the 3.23 would feel anymore.
I imagine a 3.64 diff would be quite similar, almost imperceptibly different. That said, I would choose the 3.73 again because, why not? At the end of the day, I might suggest going with whatever is easier and cheaper, if there is a difference between the two ratios. In any case, I would strongly recommend against the 3.46 rear end. I'm sure it's a difference, but believe me, these gearing changes are more subtle than a lot of people would have you believe. In fact, most of the nay-sayers I came across when I was doing my research were folks with no actual experience in gearing swaps - they were just looking at online calculators and such to come to various conclusions. Granted - you will have to adjust your shifting to accommodate the new gearset, and I suppose it is possible that one might find 3.64 "perfect" and 3.73 "too much," but I think you have to be just as careful not to under do it. This is an expensive mod, if you do it right (i.e., LSD) and the worst thing in the world would be to be underwhelmed after spending all that money. I strongly believe I would have been greatly disappointed by a 3.46 rear end, which is what I recall everyone on the forums was recommending.
__________________
____________________________ |
Appreciate
0
|
01-12-2017, 05:21 PM | #5 | |
Private First Class
26
Rep 144
Posts |
Quote:
Im not going the LSD route, as thats too expensive and the cars electronic diff isn't that bad for my use. I was looking for a swap with another BMW, a used diff if you will that i would be able to directly swap out Any ideas? |
|
Appreciate
0
|
01-12-2017, 05:47 PM | #6 | |
!
701
Rep 3,268
Posts
Drives: 2010 128i
Join Date: Feb 2010
Location: Anacortes, WA
|
Quote:
__________________
____________________________ |
|
Appreciate
0
|
01-12-2017, 08:14 PM | #7 | ||
Слава Украине!
2335
Rep 2,443
Posts |
Quote:
Quote:
__________________
|
||
Appreciate
0
|
01-12-2017, 08:38 PM | #8 |
Private First Class
26
Rep 144
Posts |
Good call on that. I'm not looking to be underwhelmed. i think I'll buy a used 328i diff 3.73, sells for around 200, if its "too much", ill change it, inexpensive enough.
What diff fluid do you guys use? II'm looking into doing my tranny and diff change, getting the redline mtl 70/80 for manual tranny, but what about the diff? Anything else I'm not considering in this endeavor? |
Appreciate
0
|
01-12-2017, 08:52 PM | #9 | |
Слава Украине!
2335
Rep 2,443
Posts |
Quote:
__________________
|
|
Appreciate
0
|
01-12-2017, 09:10 PM | #10 | |
Private First Class
26
Rep 144
Posts |
Quote:
Thanks supergnat |
|
Appreciate
0
|
01-13-2017, 04:46 AM | #11 |
Lieutenant
278
Rep 400
Posts |
Interesting thoughts,
I am close to doing the lsd. The auto from the wagon I have is a 3.91 . I think that might be too short. For me the 3.64 is the direction I'm going. At this point I have AA headers, 3 stage, (getting ready for tune) 135 brakes and square 18x8.5. the car is going to be a weekend fun and a hpde car. anyone else think thats the way to go? |
Appreciate
0
|
01-13-2017, 04:37 PM | #12 |
Second Lieutenant
94
Rep 269
Posts |
FWIW, the 128i 6-sp that I bought came with a Wave Trac limited slip. The ration is 3.46, and to me, it is very nice. I can't compare with higher numerical ratios, but this seems effective for my driving.
|
Appreciate
0
|
02-04-2017, 07:20 PM | #13 |
Brigadier General
300
Rep 4,040
Posts
Drives: 130i coupé ;)
Join Date: Nov 2011
Location: Bimmerpost
|
I have swapped my diff for 3.73 auto with out LSD - its derivable and improved my city fuel econ. Hwy Fuel is okay too if I keep it at 120km/h.
That said I do think 3.64 is the better ratio for balance of hwy and street. My motivation for 3.73 was ease of finding a good deal, and easy fit because (I may be wrong, but) the 3.64 is only possible with custom LSD equipped pumpkins OR with a drive shaft mod to mate up to a junker 3.64
__________________
128i Sport 6MT converted to Euro 130i spec, 3.73 diff, tuned by evolve ~220 whp 207 wtq(ft-lb) SAE
In-progress: //M front arm, M3 rack, e36M lip Wishlist: Coils, n55 mnts, headers, LSD, e60 finn diff "The 1-series is the last car that BMW engineered before the Germans, as a car-making culture, fell out of love with driving." - R&T 2013 135is |
Appreciate
1
ornicar136.00 |
02-08-2017, 09:43 AM | #14 |
Banned
2465
Rep 9,004
Posts |
What is the max speed in 2nd gear with the 3.73? I hae a 7500RPM redline, which goes to 70mph - that's too much, but good for autocross. I'm more interested in the torque multiplication.
|
Appreciate
0
|
02-08-2017, 01:36 PM | #15 |
Слава Украине!
2335
Rep 2,443
Posts |
60.72 MPH with a 225/45R17 @ 7500 RPM.
__________________
|
Appreciate
0
|
02-08-2017, 03:04 PM | #17 |
Слава Украине!
2335
Rep 2,443
Posts |
Attached is a zipped gearing calculator I made. Play with this if you'd like.
Fields A2, B2 and D2 are Tire x-section, tire aspect ratio and wheel diameter. Fields B7-12 are the transmission gear ratios. Entered are the stock 128i numbers. Field B13 is the diff ratio. B14 is engine red line, B15 is Torque peak and B18 is the stock diff ratio. A5, B5 and D5 are the tire parameters calculated from Fields A2, B2 and D2. Min and Max are calculated from the Torque Peak (Min) and Redline (Max). Redline shift is what the engine RPMs drop to when the transmission is shifted to the next gear from redline (for example, when shifting from 1st to 2nd at 7500 RPM with a 3.73 diff, the engine will drop to 4362 RPM). Field H6 and below are stock values for comparison and field I6 and below is the difference in MPH from Field D6 and below to field H6 and below.
__________________
|
Appreciate
2
Taskmaster2465.00 mmmusty25.50 |
02-09-2017, 01:43 PM | #19 | |
Banned
2465
Rep 9,004
Posts |
Quote:
|
|
Appreciate
0
|
02-09-2017, 06:26 PM | #20 | |
Brigadier General
300
Rep 4,040
Posts
Drives: 130i coupé ;)
Join Date: Nov 2011
Location: Bimmerpost
|
Quote:
http://www.1addicts.com/forums/showp...&postcount=964
__________________
128i Sport 6MT converted to Euro 130i spec, 3.73 diff, tuned by evolve ~220 whp 207 wtq(ft-lb) SAE
In-progress: //M front arm, M3 rack, e36M lip Wishlist: Coils, n55 mnts, headers, LSD, e60 finn diff "The 1-series is the last car that BMW engineered before the Germans, as a car-making culture, fell out of love with driving." - R&T 2013 135is |
|
Appreciate
1
Taskmaster2465.00 |
02-09-2017, 07:45 PM | #21 |
Слава Украине!
2335
Rep 2,443
Posts |
Yes, 6-speed manual. The one Andrey posted looks a lot fancier, though results should be similar.
__________________
|
Appreciate
1
Taskmaster2465.00 |
02-10-2017, 09:43 AM | #22 |
Private First Class
26
Rep 144
Posts |
Im going to look for a 3.73 ratio diff to buy, what do you guys recommend I look for?
From what car? Anything else to look out for or note? |
Appreciate
0
|
Post Reply |
Bookmarks |
|
|