Best LSD diff for M42 cars

[freeride53]

What are you guys running on your m42 powered cars with g240s?
I want something that would be nice for daily cruising on the highway as well as the (more than) occasional spirited driving.

[tak7]

4.27 from a 318ic would be perfect, though not easy to come by.
Stock 4.10 is decent, and a 4.45 might be a bit high strung.

[series88]

I was gonna ask....do all 318 verts have 4.27?

[tak7]

I was gonna ask....do all 318 verts have 4.27?

I'm pretty sure, not all LSD though.

[series88]

Gotcha. I always wondered. Never checked mine though

[jntar]

I wouldn't go with the 4.27 or 4.45 if you do a lot of highway and interstate driving. Put the engine way up in the rev range.

[bmwm42]

3.73

[RUFFLZ]

repetitive title is repetitive

just fuckin witchu booboo ;)

[bmwguy325is]

Im happy with the way Metric Mechanic built mine

[Simon S]

I’ve done a lot of general research on the matter.. and am currently running a 4.10 small case LSD (essentially what the factory intended).

The 4.10 has been working great. First gear is a little short – but overall, the gearing remains fun at highway speeds. In other words: I can “slow-creep” stop signs via second gear – and if I’m out on the freeway (~75mph), fifth gear does have an acceptable “brisk”-factor. In a dream world, my g240 would have a sixth gear for highway travel.

3.73 is the bee’s-knees for better mileage, but the trade-off is a heavier medium-case pumpkin.

Given the give-and-take of ratio-trade-offs, the factory 4.10 does its job acceptably well – but if you’re going with forced-induction – or are driving boat-loads of highway miles, then the medium pumpkin, 3.73 LSD is the tab of LSD you’ll want to drop.

[roguetoaster]

3.73 is the bee’s-knees for better mileage, but the trade-off is a heavier medium-case pumpkin.

There is nothing wrong with some low down weight in the rear of an E30 IMHO, especially in wintry weather.

As far as the best ratio either 3.73 or 4.1 are fine, the 4.1 makes it a more zippy car, but the difference is slight, mostly noticeable in 2nd and 3rd gears for power (increased speed range) and a minor RPM reduction at cruising speeds in 5th.

[decay]

4.10 torsen from a Z3. for the street, torsens fucking rule- i was very happy switching from the clutch-type.

[Ian Bowers]

Having driven Travis Ragona's E30 with a 4.10 LSD (318iS) and mine with the 3.73, I'd say go 3.73 for a DD, 4.1 for enthusiastic dickwadery. The 3.73 put me at 3k rpm at 70MPH, and I made 35mpg driving from my house to San Jose a few years back. Daily driving the car, I felt it was about perfect.

But when I started drifting the car and doing track days, it really showed how gutless the M42 is under 3k. There were a few turns at thunderhill in particular that made me hate the 3.73. I couldn't spin the tires in 3rd, but I was bouncing revlimit in second. The 4.1 would have given me that happy medium.

.02

[e30Chris]

I'm so happy with the 4.10 in my car, I'm having a hard time seeing why anyone would switch. Sure, it's a little high-strung on the highway, but it just makes me keep it between 65 and 70. No tickets, and decent gas mileage (high 20's, low 30's). Considering the lack of power from the M42, in stock form the car doesn't FEEL slow. I think it's all in the gearing. I love it.

[djmossm42]

I was under the impression all 318iS had 4.10 LSD standard as well as iC. So is the 4.27 in the vert to make up for the extra weight? Pretty sure I have an LSD but never verified it but whenever the back gets loose it feels like both wheels are turning together and it's very controllable. I'll take a look today and see what I have going on.