M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => General Topics => Topic started by: mrklynch on October 30, 2010, 05:37:11 AM
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Hi guys, new to this and need some good info and advice please, I have found a m3 3.0 for breaking and the guy offered me the whole rear end, ie diff, drives etc.,, now i just need to know is this a good swap to my 1996 318is 1.9? what gains or dis-advantages would i be getting? I googled it but it got confusing to me, i know the diff of my own 318 gear ratio is different to the m3 diff but i am confused as to what changes it would make, can someone please fill me in on everything that i would need to know.
Thanks Guys
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What's the ratio on the M3 diff? I know it's not as steep as the 4.10, but I'm not sure what the ratio is. Regardless, you're going to have slower acceleration and lower RPMs at high speeds in 5th.
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didn't e36m42 cars come with something taller than a 4.10? i thought they had a 1:1 5th...
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I'm pretty sure the USA M3 had a medium case 3.15LSD but I'm told the Euro M3 has a large case & I'm unsure of ratio. I think it's a 3.23. It should be on the diff somewhere, on a tag or label. If not, google it. I found too much contradictory info though. I'm thinking it a bit too low a ratio for your motor, but you'll get a bump in fuel economy and quieter highway running.
I found this page (http://forums.bimmerforums.com/forum/showthread.php?t=714102) about it, the US e36 is mechanically the same as the Euro e36 AFAIK. Should swap right over if you get the entire rear subframe in there. Since you're getting the whole rear end that won't be a problem.
If you don't understand a diff, here's the skinny: The ratio is the number of times the input shaft (off the tranny) will spin for every output revolution (to the wheels). So if you have a 4.1, you'll get one wheel rotation for every 4+ incoming. Great for little motors like ours, it's called a 'short' diff (because it runs out of revs quickly). The motor has a lot of mechanical advantage too, so it'll get the car moving faster. However, it'll eat more gas & run high RPMs on the highway.
As you cut that ratio down ("taller" diffs), each engine rpm gets you less advantage. So the car gets slower. The transmission output has to only turn three times for each wheel revolution though, so you'll get more top end and each gear will "last longer."
My e30 318i had an open 4.1. It went bad so I swapped in a 3.73 LSD. The car is noticeably slower, but I get better fuel mileage and it runs better on the highway. The power band is perfect for US driving conditions. 70MPH (120KPH) is maybe only 3500rpm in 5th gear, right smack in the middle of the power band.
School buses are faster from a dead start though...
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http://www.unixnerd.demon.co.uk/bmw_e36.html
looks like 3.45 for the M42 car, and 3.23 for the M3.
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http://www.unixnerd.demon.co.uk/bmw_e36.html
looks like 3.45 for the M42 car, and 3.23 for the M3.
Good link deekay,
will this make a big difference to my car? Had the intentions of doing a little drifting and the odd donut, track near me and they hold a diff and drift day maybe once a month, getting tired of just being a spectator. So would this LSD be ok for me?
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If they're that close you wouldn't see much difference. The bigger M3 diff will add a few pounds. I don't know how well the LSD will do at drifting though...once it locks up I'll bet it'd be OK. We don't have a whole lot of torque to play with here.
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well i suppose i am just gonna have to find out the hard way, no harm in trying it, however i may think that the ratio will definetaly improve my mpg as it does tend to be in sorta high revs all the time, in 5th gear i'm 98% sure that at 60mph im at 3500rpm or very near that and always thought that to be high for a 1.9 engine,but currently doing 30mpg,, i also have a 2.0l vauxhall vectra and at 60mph in that its around 2600rpm.
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Sounds about right..... since you probably don't have an overdrive in your tranny.
~Ralph
Enter Gear Ratio : 4.10
Width Aspect ratio Diameter
Enter Tire Size: 205 60 15
1st 2nd 3rd 4th 5th
Ratio: 4.23 2.52 1.66 1.22 1.00
( E36 M3 ratios)
RPM 1st 2nd 3rd 4th 5th
750 3 5 8 11 13
1000 4 7 11 15 18
1250 5 9 13 18 22
1500 6 11 16 22 27
1750 7 12 19 26 31
2000 8 14 22 29 36
2250 10 16 24 33 40
2500 11 18 27 37 45
2750 12 20 30 40 49
3000 13 21 32 44 54
3250 14 23 35 48 58
3500 15 25 38 51 63
3750 16 27 40 55 67
4000 17 28 43 59 72
4250 18 30 46 62 76
4500 19 32 49 66 81
4750 20 34 51 70 85
5000 21 36 54 73 90
5250 22 37 57 77 94
5500 23 39 59 81 99
5750 24 41 62 84 103
6000 25 43 65 88 107
6250 26 44 67 92 112
6500 28 46 70 95 116
6750 29 48 73 99 121
7000 30 50 76 103 125
7250 31 52 78 106 130
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will this make a big difference to my car? Had the intentions of doing a little drifting and the odd donut, track near me and they hold a diff and drift day maybe once a month, getting tired of just being a spectator. So would this LSD be ok for me?
at this point we're venturing out of the area of hard numbers, into that of opinion- just so you know that's what you're getting here.
given the intent of enthusiastic use, i think you're gonna want to upgrade the clutch- track days alone would warrant it, but going to a slightly taller gear is going to put higher requirements on those parts also.
i'm not saying you have to do this right away, but if you put in the taller diff and take it to drift events, you should plan on a better-than-factory clutch before you need it (especially if this is a daily driver car).
as far as the ratio goes- like Dave said, that's not so big a change as to make the car unusable. if you're willing to take some weight/driven mass out of the car, as i've done with mine (lighter driver/passenger seats, AC/PS/clutch fan gone, rear seat gone, etc), you might not even notice the difference.
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For any larger case diff, you need the 6-cylinder axles, the diff itself, and 6-cylinder driveshaft too, since it is quite a bit shorter than our stock E36 168mm diffs.