LSD off of an automatic

[hickatew]

I'm considering buying a used LSD off of an automatic ZHP. I don't see why it would make a difference that it's automatic but looking at the listing for the MFactory LSDs (https://www.ecstuning.com/News/BMW_E46_325i_325ci_328i_328ci_330i_330ci_MFactory_ Limited_Slip_Differential_1999_2000_2001_2002_2003 _2004_2005_2006/), they differentiate between auto and manual transmission. My ZHP is manual, will it work?

[slater]

it should work - just confirm that the diff has a 6-bolt input flange.

[Sockethead]

The axle flanges are different than the manual but they can be swapped

[hickatew]

The axle flanges are different than the manual but they can be swapped

That for sure? I found this too https://www.bimmerforums.com/forum/showthread.php?2148520-E46-non-M-Rear-Differential-Output-Flange-Output-Shaft-Differences

[Reasoned1]

I assume that's a 3.64--I just ordered one from M-Factory... REALLY looking forward to installing and driving it. I'm no expert but, in all my research (which has been extensive, to say the least), I never encountered any cautions about manual versus automatic--quite the contrary, in fact. They get mixed and matched all the time. The most important consideration, as slater mentioned , is the flange type (input and output, but input is what really matters since the output flanges can be easily swapped with your current ones). Of course, we're talking about RWD vehicles only here... otherwise, there are other, extremely important considerations.

[Sockethead]

The LSD diff I got from Diffs online had automatic flanges... different bolt pattern. You can pop them out with a pry bar and swap your manual flanges... that's what I did. The Pinion flange needs a little more work since it should be pre-loaded. Mine already had the 6 bolt pinion flange on it.

I believe it's the non ZHPs that have the 4 bolt pinion flange but I'm not entirely sure...

[slater]

The LSD diff I got from Diffs online had automatic flanges... different bolt pattern. You can pop them out with a pry bar and swap your manual flanges... that's what I did. The Pinion flange needs a little more work since it should be pre-loaded. Mine already had the 6 bolt pinion flange on it.

I believe it's the non ZHPs that have the 4 bolt pinion flange but I'm not entirely sure...

basically all 5-speed E46s got the 4-bolt flange... we didn't see the 6-bolt until 3/03 when the 6-speed 330's because available.

and yes, the axle flanges are easy to swap. my MFactory diff also came with 5-speed axle flanges (and a 4-bolt input flange... not a welcome surprise... but it wasn't their fault).

[hickatew]

Great info, thanks all!

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[cornercarver]

A 3.64 ratio is going to make 1st gear almost useless, but should make 2-5 a lot more fun.

edit; BTW hickatew - is this the diff you asked about in GDMChRiZ's classified thread? How do you know it's an LSD?

[Reasoned1]

Torque and speed are proportional to gearing. So, since 3.64 is 7.7% greater than 3.38, redline speed in any gear will be 7.7% lower for 3.64 than for 3.38. Thus, if I currently redline in 1st at 35mph with my 3.38, I divide 35mph by 1.077 to figure out I’ll redline at 32.5mph in 1st with the 3.64. The difference, while significant, isn’t dramatic and won’t make 1st gear useless, in my opinion. My biggest concern in going with 3.64 is excessive rpm at highway cruising speed, but the calculations show I’ll still be under 3,400rpm which, for me, is tolerable (especially since this car doesn’t see much Interstate) and is worth the benefits.

Another tantalizing calculation is that, assuming my modified car is making 225lb-ft of peak torque at the flywheel, the torque multiplying effect of the shorter, 3.64 gear ratio will make the wheels see a torque 18.5% greater than that seen with the stock, 3.07 gear box—as if the engine were generating a peak torque of 267lb-ft! That’s why changing the final drive ratio is known as a “poor man’s supercharger”.

Of course, there are trade-offs—the big one being reduced top speed, but the calculations also show the 3.64 still has a theoretical top speed in excess of 160mph which is both impractically fast and getting to the point where drag makes going faster impossible for available power anyway. Another possible trade-off, for some people but not me, is that the shorter gearing makes it necessary to shift sooner and changes the position of shift points relative to speed.

[Sockethead]

I had 4.57 in one of my cars long ago and while it was perfect at the drag strip, 3000 rpm was at 55 mph.. It was fun for a while then I got sick of it and swapped for 4.11.
I had a 3.46 in my ZHP but swapped it out for 3.15 because I do a lot of highway driving.

[hickatew]

A 3.64 ratio is going to make 1st gear almost useless, but should make 2-5 a lot more fun.

edit; BTW hickatew - is this the diff you asked about in GDMChRiZ's classified thread? How do you know it's an LSD?It's not, I asked. It's the stock open diff. But before I knew that I started this thread [emoji28]

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[Reasoned1]

Still might be great to install—depending on price. It might at least hold you over until you get an LSD.

[Reasoned1]

Sad, sad news... MFactory called, and they were unable to build the 3.64, so I have to content myself with a 3.38. Oh well... tears running down cheeks...

[ELCID86]

That was the better choice anyway;-)

[BMWCurves]

Sad, sad news... MFactory called, and they were unable to build the 3.64, so I have to content myself with a 3.38. Oh well... tears running down cheeks...

It's the final drive ratio I plan to get if I ever go through with an LSD.

[Reasoned1]

Thanks for the words of consolation, Shawn—maybe it is for the best. Of course, now I’m probably going to have to get a supercharger... :)

[Sockethead]

Try headers before the supercharger... you'll get a lot of torque from that... if you're not satisfied after that then the headers will just enhance the supercharger

[Reasoned1]

I would love to do headers but, from what I gather, they come with various emissions issues and seem relatively expensive, once all is said and done with the whole exhaust, for relatively minor gain. Is it feasible to run a supercharger with stock headers/exhaust?

[Sockethead]

I wouldn't call it minor... It made a significant difference IMO.
I guess it all depends on whether your state does emission inspection or not
Yea there is no problem running stock manifolds/exhaust with a SC.