What Differential?

[325is_MadBimmer]

Ok so i have a 1990 325is and am wondering what differntial I have. Is it a 3.23 LSD? and upgrading it to a 3.73 would increase acceleration but lower top speed correct?

[Jordan]

you have a 3.73:1 LSD from the factory.

[bwanac]

3.73 LSD most likey.

You would need to upgrade to a 4.10 to get a little more acceleration!

EDIT: Damn, The J man beat me.

By the way Drew (randomtask73) may still have his 4.10. But shipping is not fun!!! :shock:

[Jordan]

4.10 in an otherwise stock 325iS is a complete and utter waste of time, money, and fuel.

PERFORMANCE COMPARISON ANALYSIS
-------------------------------

Selected Cars:
1. BMW 325IS 1987 STOCK
2. BMW 1987 325IS 4.10
3. BMW M3 1989

Car Number 1 2 3
--------- --------- ---------
Time to Speed
0-30 mph.... 2.3 2.3 2.4
0-40 mph.... 4.1 4.0 3.3
0-50 mph.... 5.4 5.3 5.4
0-60 mph.... 7.8 7.7 6.9
0-70 mph.... 9.9 9.6 8.8
0-80 mph.... 12.2 12.1 12.1
0-90 mph.... 16.1 15.9 15.0
0-100 mph.... 20.1 19.6 18.4

Time to Distance
0-100 ft..... 3.3 3.3 3.2
0-500 ft..... 8.6 8.6 8.4
0-1320ft..... 15.7 15.8 15.5
@ mph .... 89.0 89.5 91.5

Top Speed.... 138 134 141

5-60 mph, 1st
Gear Start... 7.4 7.2 6.9

30-50 mph
2nd Gear..... 2.4 2.3 2.9
3rd Gear..... 4.1 3.7 5.2
4th Gear..... 6.7 5.8 8.8
5th Gear..... 9.5 8.0 12.9
6th Gear.....

50-70 mph
2nd Gear..... 3.3
3rd Gear..... 4.1 3.7 5.1
4th Gear..... 6.4 5.6 8.3
5th Gear..... 8.9 7.6 12.0

[325is_MadBimmer]

man thanks guys, damn that is some low low low gains. Would it make a difference that i have a chip and exhaust?

[e36sport]

Good info Jordan, you probably saved a bunch of people a chunk of change.

[schnitzer teil-jäger]

3.73 vs 4.10
if you autocross and find out your local tracks make you shift too often from 1st to 2nd you can put in a 4.10 and your times will come down
if you shift from 2nd to 3rd too many times you may need to go back to a 3.73
You can change your diff to achieve the least number of shifts. each shift costs more time than either diff will gain or loose over the course. you do not want to shift only feet before the end of the straights.

drawn the course at the next event and mark all your shift points and gears. then ask will the 30.00 ebay chip give me 6-700rpm and get me to the corner without changing gears???? or do I need to spend 400.00 on a 4.10 LSD to get into the gear earlier so I can make up the lost time from shifting.

w

[randomtask37]

i dont know much about those #'s, but ill tell ya, my car felt like a whole new animal once i got that 4.1 installed. i would reccommend it if you have the money to spend.

p.s. yes i do have one for sale if your interested. ;)

[Low Level E30]

Not quite sure where you got the numbers, J, but it really doesn't matter.

What does matter is that if you ask any of the open road course guys that run 4.10s, and I can name a few very good ones, they'll tell you that it is a noticeable and worthwhile upgrade for a 325i(s). Some of those guys even run 4.27s.

I have a 4.10 on my 325is, and it has been an excellent upgrade.

Again, I'm not certain where you got your numbers, and how valid they are - but let's assume they are valid...

... check the 30-50mph and 50-70mph times - the difference there between a 3.73 and a 4.10 is pretty substantial - this is the advantage, a lot of extra punch in the middle gears, and 5th becomes useable as an accelerating gear. Given the brick-like aerodynamics of an E30, you'll have a tough time finding a road course with a straightaway long enough to reach the top speed of 130mph+ --- and I don't even know if a 3.73-equipped car can reach its theoretical top speed.

And really, I bet you'd have a tough time finding many racecars that retain a stock diff ratio, be it a BMW or anything else.

Point is, a 4.10 can definitely be a worthwhile upgrade - but like anything, it comes down to what kinda use you're gonna get out of it. If you're talking about a basically-stock E30 to bumble around town in, you'd probably want to keep the 3.73 since gas prices are going up, and you're not wringing max performance out of the car between stoplights, no matter how fast you think you are. If you've got 100lbs of bump in the trunk, then mebbe a 4.10 would be good, since you've shot yourself in the ass with all that extra weight :twisted:....

But if you're really gonna drive the car, consider a 4.10.

[e30Matt]

:stupid:

[decay]

not like those are the only two ratios available anyway...

[Rob]

those numbers are very very subjective, I would think on different days with different drivers, they could vary drastically.

[Charlie]

A 4.10 rear end makes a night & day difference on an 'is. Do it.

-Charlie