E30 318is M54b30 swap Differential upgrade

[Guwop_E30]

Hey guys if anyone can help or point me in the right direction I would gladly appreciate it. I know nothing about differentials and I am in the process of putting my m54b30 swap into my e30. I am planning on putting a turbo in the car as well so I know I have to swap the rear differential. I am having a hard time figuring out what differential I am able to run and what would be the best option for me. I am not looking for a headache with this lol I just need to know what I should get. I get confused when I see a bunch of different options. I’m am looking to beat on the car sometimes but also enjoy the car on the highway when I want. Thanks in advance.

[monty23psk]

I have an 318is and went from a 4.10 open to a 3.73 lsd. I did this as I have will also add a m54 to the e30 in the future. (need to pull it from my e39 parts car). In talking to diff rebuilder, the 3.73 would be the best of both worlds. Today with the m42, my 4th gear is very long and getting very nice mpg on the highway. It did loose a little of the peppiness in 1st gear with the 4.10.

[roguetoaster]

It really depends on what transmission you are using. There are plenty of gearing calculators around that allow you to input tire size, transmission ratios, and differential ratios to see an approximate speed/RPM in gear. Use that to figure out where you want to be on the highway, and compromise from there since that is the vast majority of most driving.

Either a small case (E30, E36 318ti & Z3 4 cylinder models), or a medium case from the remainder of the E30 lineup are all going to work in terms of actual fitment, even if you have to change differential output flanges to match your axles.

[TobyB]

If you're using the ZF320 or another 1:1 5th speed,
I'd suggest an eta LSD if you can find one- my 330ci has a 2.91
diff, and it launches ok (for a 3400 lb pig) but cruises pleasantly at 2500- 3k rpm.
Turbos can add torque, and off you go.

If you're using the 260 or other 1:1 4th gear 5 speed,
go numerically lower- 3.73 is probably TOO low, though, as the 3 liter makes a buttload of torque,
and will pull just fine from below 2k rpm.

Now, if you're all about the drifty burnouts, the 3.73 is fine.

t

[Vincenze]

The m54b30 comes with the 6-speed GS6-37BZ transmission.

The ratios are here: https://en.wikipedia.org/wiki/ZF_S6-37_transmission

Use a gearing calculator https://diffsonline.com/bmw-differen...formation.html

[roguetoaster]

M54s also come with 5 speeds, ask me how I know. You can also fit many other possible transmissions behind them.

[Vincenze]

M54s also come with 5 speeds, ask me how I know. You can also fit many other possible transmissions behind them.

That would be a bad transmission for highways as the 6-speed has the same 5 gears PLUS 1 overdrive gear.

[roguetoaster]

That would be a bad transmission for highways as the 6-speed has the same 5 gears PLUS 1 overdrive gear.

Sure, in theory the 6 gang might be better, but the 5 speed works just fine in an E39 with 3.15s, and you don't have to downshift to pass on the highway.

[Vincenze]

Then, there are many relatively low-mileage 3.15 and 3.07 Z3 Torsen differentials. They are the newest that fit.

[TobyB]

The m54b30 comes with the 6-speed GS6-37BZ transmission.

in the 330ci post- facelift. The xi got a 5 speed, and the i came either way.

When the b30 came with a 1:1 final transmission, the car got a low numeric rear, in the 2.9- 3.1 range.
The overdrive 6ths got a numerically higher rear.

fwiw,
t