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Posted
Monday, Jun 11th 1:56am [Edit] [Quote] [IMS] [View car] |
Post nr. 171
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my stock 3.25diff is leaking bad, thinking about replacing it with a 3.91 LSD. My top speed will go down, and so will my gas mileage no? but it will be more fun around town? Just want to check on these things, anyone have a guestimate on how much my gas mileage will go down? |
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Posted
Monday, Jun 11th 2:15am [Edit] [Quote] [IMS] [View car] |
Post nr. 184
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There have been different views on this, but I don't like the 3.91 with the m20. It makes it too high strung, especially with a 4-speed. It was better after I installed the 5-speed, but low end traction suffered. Too much gear for an effective launch. MPG will suck with a 4gear unless it's all in-town driving. My opinion only, does not necessarily reflect the opinions of this forum.
--Dennis
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Posted
Monday, Jun 11th 5:18am [Edit] [Quote] [IMS] [View car] |
Post nr. 1127
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I am 100% with Dennis on this. I have a 4 speed with the 3.45 and I cannot imagine the 3.90. First gear will be near useless. |
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Posted
Monday, Jun 11th 6:26pm [Edit] [Quote] [IMS] [View car] |
Post nr. 287
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U would probably get wheelspin with the 3.91.
Since your 3.25 is leaking, why not replace the seals/gaskets? Are the parts not available where you are? |
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Posted
Monday, Jun 11th 8:13pm [Edit] [Quote] [IMS] [View car] |
Post nr. 133
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3.25 on a e21??? |
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Posted
Monday, Jun 11th 9:28pm [Edit] [Quote] [IMS] [View car] |
Post nr. 172
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I have the dogleg sports 5speed gearbox and im assuming that came with the 3.25 no?
I want an LSD,
I would be happy if i can find a 3.45 on ebay and will look. I think It would be significantly easier for me to buy a 3.45 LSD on ebay and have it installed than to fix the one i have unfortunatly.
Fixing the one i have would be around 400usd with lost acess to car for a day-harsh-im in California in the Valley.
Installation of a new one would be 100dlls, and an LSD off ebay i can get i think for 300 or less.
3.45LSD with the dogleg then? good combo? could it be that i already have a 3.45, or did the dogleg always come with the 3.25. I dont know if this matters but i have the 323i sports suspension, ie the bigger sway bars and the stock bilsteins-i believe the car came this way... |
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Posted
Tuesday, Jun 12th 4:15am [Edit] [Quote] [IMS] [View car] |
Post nr. 184
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Again, the BMW ETK shows no reference whatsoever to a 3.25 ratio in the diff. It shows all 323i's to have a 3.45. I am not sure where this rumor started, but I have never seen evidence that it is true. You likely have a 3.45 diff.
--Dennis |
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Posted
Tuesday, Jun 12th 5:00am [Edit] [Quote] [IMS] [View car] |
Post nr. 62
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I'll chime in on this one. Having the dogleg attached to a 4:75LSD I can say 1st isn't useless, but it will redline quick if you aren't watching.
I made a video of my car and you'll get the idea what range the rpm's run normally. It's fun, but long distance interstate driving can make for a stiff back.
I'd think the 3:90 would be a good overall choice, without losing that much in gas vs what you gain in fun.
http://www.youtube.com/watch?v=gNS63mTx_jY |
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Posted
Tuesday, Jun 12th 9:55pm [Edit] [Quote] [IMS] [View car] |
Post nr. 173
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About the 323i
The 323i also came standard with a 4-speed gearbox, however most 323i are equipped with a 5-speed overdrive gearbox. A dogleg close-ratio sport gearbox was available as an option.
The 323i has a 3.45:1 ratio on the differential. If fitted with a sport gearbox, the ratio was 3.25:1.
source- http://e21.tricord.be/e21/about/m20/gearbox-info.php
What is the part number on the seal that is probably leaking, i cant find the right diagram on realoem, anybody ever had one of these leak before. Its leaking from the front.
-g323 |
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Posted
Tuesday, Jun 12th 11:11pm [Edit] [Quote] [IMS] [View car] |
Post nr. 1129
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I am not aware of a 3.25 for the e21. |
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Posted
Wednesday, Jun 13th 2:41am [Edit] [Quote] [IMS] [View car] |
Post nr. 363
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Disregard, I'm an idiot. |
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Posted
Wednesday, Jun 13th 4:50am [Edit] [Quote] [IMS] [View car] |
Post nr. 1130
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To each their own but I don't see it. Most of the m20 engines here aren't making much power past 5300 rpm. The 3.91 is going to put you out of the fat torque band. |
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Posted
Wednesday, Jun 13th 9:33am [Edit] [Quote] [IMS] [View car] |
Post nr. 51
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| g323 wrote: | About the 323i
The 323i also came standard with a 4-speed gearbox, however most 323i are equipped with a 5-speed overdrive gearbox. A dogleg close-ratio sport gearbox was available as an option.
The 323i has a 3.45:1 ratio on the differential. If fitted with a sport gearbox, the ratio was 3.25:1.
source- http://e21.tricord.be/e21/about/m20/gearbox-info.php
What is the part number on the seal that is probably leaking, i cant find the right diagram on realoem, anybody ever had one of these leak before. Its leaking from the front.
-g323 |
yeah its definatly short through the gears...
OT: love the exhaust note  |
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Posted
Friday, Jun 15th 12:56pm [Edit] [Quote] [IMS] [View car] |
Post nr. 531
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It's a roughly linear relationship, according to an extensive vehicle study I did.
On a manual transmission car, a 10% numerically taller Final Drive ratio will improve fuel economy on motorway ahd highway cruises by about just under 6%
A 10% shorter FD ratio will decrease fuel economy by about just under 6%.
An automatic transmission shows less sensitivity, although it must be said that the study was carried out in 1997 and with alot of American vehicle data. Mainstream yank cars have/had prehistoric automatic transmissions compared to the state of the art Euro stuff, however this means it is probably quite relevant to our E21.
I did researh on the 3.25 rear end in an E21 and I think it was probably a myth propagated by the Haynes workshop manual for LSD cars.
Assuming it is a myth- going from 3.45 to 3.91 represents about a 13% change. So you can probably expect about a 7% drop in fuel economy.
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Posted
Friday, Jun 15th 3:23pm [Edit] [Quote] [IMS] [View car] |
Post nr. 1271
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| BruceH wrote: |
To each their own but I don't see it. Most of the m20 engines here aren't making much power past 5300 rpm. The 3.91 is going to put you out of the fat torque band. |
I am going to find out. I have a 3.91 LSD that I am going to put in with a 4 speed.
Should scream off the line. I dont plan for highway driving anyway. Top end speed is overrated. Shift, turn, accellerate, shift is where the fun is. |
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Posted
Friday, Jun 15th 10:48pm [Edit] [Quote] [IMS] [View car] |
Post nr. 194
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May not be an issue in this case, but don't forget to factor in any pending tire/wheel diameter changes - I went from a 3.64 open diff in a US spec M10 320i with an OD 5 speed to a 3.91 LSD and replaced the 13" wheels and 185/70s with staggered 15's (15x6 & 185/60 front, 15x7 & 205/60 rear) at essentially the same time.
The end result was virtually zero change in rpm vs speed - the larger diameter wheel/tire combo exactly offset the lower diff gearing. |
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Posted
Saturday, Jun 16th 6:35am [Edit] [Quote] [IMS] [View car] |
Post nr. 1056
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i would argue that unless you're running an M20 with webers and a 300 degree duration camshaft a 3.91 is a complete waste of effort compared to the stock 3.45.
I think the 3.25 myth was propagated because of the E30 323i. I think (but haven't checked in ETK) the the E30 323i was equipped with a 3.25 when it had the dogleg box.
jamie |
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Posted
Sunday, Jun 17th 7:05pm [Edit] [Quote] [IMS] [View car] |
Post nr. 63
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| MayanArch wrote: | | Should scream off the line. I dont plan for highway driving anyway. Top end speed is overrated. Shift, turn, accellerate, shift is where the fun is. |
That's what I'm talking about..... |
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