[IMS-340C]

Interesting, Funny I am going the complete opposite direction

So did you compare speedometer with GPS ? Also how much slower is the car now ?

My 340i RWD 8AT's VIN says I can run either 2.81 or 3.15 (attached)

3.15 Diffs are selling as low as $150 on ebay, if it works it would be the best performance upgrade for a very little cost.

Originally Posted by RumDomRum

I just did the diff swap today.

I have a 2019 440i Coupe MANUAL. It came with a 3.23 rear differential and an 0.845 6th gear.
I also own a 2019 440i Gran Coupe xDrive with the Auto. The auto came with 2.81 rear diff and a 0.634 8th gear.

At 90mph with the GC Auto my RPM is 1950. With the manual at only 80mph it was running 3100 RPM. I don't remember what it is at 90, but I think it was around 4k. I HATE the difference between the two because honestly, I liked getting almost 40mpg in the auto and hated getting only 29mpg in the manual.

So I purchased the M-Performance LSD diff in 2.81 (PN: 33108659989) and put it in the manual 440i.

Verdict: It's great.

Now at 80mph I'm at 2500rpm. It's never going to be as good as the auto since top gear is such a different ratio, but I'm enjoying every gear more. Now, if I lose grip on a hard accel, both rear tires go and the car doesn't do the side to side shimmy that is sometimes terrifying. The car is much more predictable and feels better planted.

The swap was straight forward and everything fit. All you need is a 50mm wrench (I purchased one from Harbor Freight) and normal BMW fitment tools (couple torx, 10, 13, 16 and 18mm).

Only issue I have discovered: RevMatch is now non-functional. I'm guessing I need to find some way to tell the DME the ratio is different. No fault codes, no lights, no drivetrain malfunction indicators, nothing. Speedo is still correct, as well.

[RumDomRum]

Car doesn't seem any slower at all. No reason for it to be slower; HP is still the same and I spend more time in the power band now.

First gear was already too short for the b58 on the stock turbo.

[RumDomRum]

Originally Posted by IMS-340C

Interesting, Funny I am going the complete opposite direction

So did you compare speedometer with GPS ? Also how much slower is the car now ?

My 340i RWD 8AT's VIN says I can run either 2.81 or 3.15 (attached)

3.15 Diffs are selling as low as $150 on ebay, if it works it would be the best performance upgrade for a very little cost.

yes I compared speedo.
There's no reason for the speedo to change. The wheel speed sensors are based on revolutions of the tires per mile, not the transmission. Most cars stopped using the transmission for vehicle speed over a decade ago.

[RumDomRum]

Originally Posted by mike082802

great to know and thanks for being the guinea pig. in the n54 world guys were doing this all the time, the mt was 3.08 and the auto was 3.46 and it was a direct swap, there was no such thing as rev matching back then. the mt diff carried a premium price. i am curious what 2nd, 3rd, and 4th are at redline.

it matches this calculator pretty closely.

I really dislike 5th and 6th in this trans. After the supra comes out with their manual, if the ratios are better, I will go to those. If they are not better, I'll design a new 5th and 6th to put in the case.

[IMS-340C]

If the sensor is on the transmission any point before the diff speedo will not change but if it's on the tyres the tyres rotate at a different speed so it will cover different miles.

Originally Posted by RumDomRum

yes I compared speedo.
There's no reason for the speedo to change. The wheel speed sensors are based on revolutions of the tires per mile, not the transmission. Most cars stopped using the transmission for vehicle speed over a decade ago.

[RumDomRum]

Originally Posted by IMS-340C

If the sensor is on the transmission any point before the diff speedo will not change but if it's on the tyres the tyres rotate at a different speed so it will cover different miles.

wow, it's almost like that's exactly what I said.... but backwards. You're very confused.

[IMS-340C]

Actually when I thought about it yes any readings before the diff will not be accurate.

Originally Posted by RumDomRum

wow, it's almost like that's exactly what I said.... but backwards. You're very confused.

[RumDomRum]

Originally Posted by IMS-340C

Actually when I thought about it yes any readings before the diff will not be accurate.

glad you figured it out.
Sorry I sounded like a dick.

[IMS-340C]

Anybody know what's the difference between Rear Axle Drive and Exchange Final Drive ?

[IMS-340C]

Bought a used 3.15 rear diff, since almost the whole rear axle will be disassembled what other parts do you guys recommend changing ?

Car has 40K miles - 60K Kms Thanks

[WrxToBeamerGuy]

Following.

[WrxToBeamerGuy]

Originally Posted by IMS-340C

Bought a used 3.15 rear diff, since almost the whole rear axle will be disassembled what other parts do you guys recommend changing ?

Car has 40K miles - 60K Kms Thanks

Found this setting in Bm3.

[WrxToBeamerGuy]

This is the ratio for the MPPSK map. It's different

[IMS-340C]

Confusing indeed I wonder what happens in the tune when you change this table.

Originally Posted by WrxToBeamerGuy

This is the ratio for the MPPSK map. It's different

[mike082802]

Originally Posted by RumDomRum

glad you figured it out.
Sorry I sounded like a dick.

Any updates on how everything is working? Cruise control still works? Do you notice much of a difference with the 2.81 in your manual car? I find first and second gear almost useless in the 6mt especially with an upgraded turbo.

[johnung]

Just to update this thread…
I read a few comments that stated that BMW did not make an M Performance LSD for XDrive models. That is not actually true.

When BMW was designing the F30 MP LSD probably around the 2011-2012 timeframe, it was an expensive aftermarket part, around $3,000 including installation. BMW assumed that it’s target market would be guys with F30 RWD, enthusiasts who track their cars.

At the time BMW German engineers couldn’t imagine XDrive owners tracking their cars. So the compatibility lists and MP LSD literature only listed RWD cars with either manual or automatic transmissions because their final drive ratios are different based on transmission.

The XDrive cars were using the exact same stock rear differentials with the same rear final drive ratios as the RWD cars. So the MP LSD just swaps right in and works on XDrive. It’s just that the MP LSD literature written in 2012 doesn’t say anything about XDrive.

Many people don’t see XDrive listed in MP LSD literature and immediately say that BMW doesn’t make an LSD for XDrive, which is incorrect.

To create an XDrive car, BMW essentially takes a RWD model and adds a bunch of XDrive components like front differential, transfer case, front wheel drive shafts and much more. Part differences between RWD and XDrive happen in the front half of the car. The back half of RWD and XDrive cars are close to 100% identical. I haven’t run across a difference.

UPDATE: BMW is known to sometimes do unexpected things. Always verify part numbers and specs on your own car using realoem and other resources. My car is an F30 335i XDrive Automatic.

[Kraklz]

Originally Posted by johnung

Just to update this thread…
I read a few comments that stated that BMW did not make an M Performance LSD for XDrive models. That is not actually true.

When BMW was designing the F30 MP LSD probably around the 2011-2012 timeframe, it was an expensive aftermarket part, around $3,000 including installation. BMW assumed that it’s target market would be guys with F30 RWD, enthusiasts who track their cars.

At the time BMW German engineers couldn’t imagine XDrive owners tracking their cars. So the compatibility lists and MP LSD literature only listed RWD cars with either manual or automatic transmissions because their final drive ratios are different based on transmission.

The XDrive cars were using the exact same stock rear differentials with the same rear final drive ratios as the RWD cars. So the MP LSD just swaps right in and works on XDrive. It’s just that the MP LSD literature written in 2012 doesn’t say anything about XDrive.

Many people don’t see XDrive listed in MP LSD literature and immediately say that BMW doesn’t make an LSD for XDrive, which is incorrect.

To create an XDrive car, BMW essentially takes a RWD model and adds a bunch of XDrive components like front differential, transfer case, front wheel drive shafts and much more. Part differences between RWD and XDrive happen in the front half of the car. The back half of RWD and XDrive cars are close to 100% identical. I haven’t run across a difference.

Thats absolutely not true. The xdrive models are not rwd drivetrains with awd components. Look at the part numbers. The xdrive 6 cylinder models actually use the same diff as the 4 cylinder rwd models. Because of this the xdrive models are use a smaller splined axle. People have already attempted to fit the m perf lsd on the xdrive and have found you need to change the axles and push back the diff by 10mm or so.

RWD 6 cylinder 225kw diff
AWD 6 cylinder 181kw diff
RWD 4 cylinder 181kw diff

Why did you make up that elaborate story

[Aussiefalcon]

Here in Australia I have a 2017 340i auto and 3.15 final drive ratio from factory.
USA all seem to be 2.81 in the autos.
Am I correct ?

[johnung]

Originally Posted by Kraklz

Thats absolutely not true. The xdrive models are not rwd drivetrains with awd components. Look at the part numbers. The xdrive 6 cylinder models actually use the same diff as the 4 cylinder rwd models. Because of this the xdrive models are use a smaller splined axle. People have already attempted to fit the m perf lsd on the xdrive and have found you need to change the axles and push back the diff by 10mm or so.

RWD 6 cylinder 225kw diff
AWD 6 cylinder 181kw diff
RWD 4 cylinder 181kw diff

Why did you make up that elaborate story

Didn’t make up anything. I speak from experience. I did my research and then I installed it on my own car. I have had an M Performance LSD on my F30 335i XDrive Automatic for 3+ years. It was a simple replacement swap installation. No driveshaft incompatibility at all. The incompatibility that you refer to is a specific configuration, not a broad generalization about XDrive.

[YASBBYM3]

Originally Posted by johnung

Didn’t make up anything. I speak from experience. I did my research and then I installed it on my own car. I have had an M Performance LSD on my F30 335i XDrive Automatic for 3+ years. It was a simple replacement swap installation. No driveshaft incompatibility at all. The incompatibility that you refer to is a specific configuration, not a broad generalization about XDrive.

Are you posting in the N55 or the B58 subgroup🤔

Just because the LSD worked on the RWD or the AWD in the N55, doesn’t mean it will in the B58 models. You are about to lead someone to make an expensive mistake.

[johnung]

Originally Posted by YASBBYM3

Are you posting in the N55 or the B58 subgroup🤔

Just because the LSD worked on the RWD or the AWD in the N55, doesn’t mean it will in the B58 models. You are about to make some make an expensive mistake.

Wasn’t posting to any subgroup. When the application lists New Posts to read it provides all 2012-2019 3&4 Series without identifying any subgroup where a post may have originated. That’s why I added more specific details.

[weehe126]

Originally Posted by johnung

Wasn’t posting to any subgroup. When the application lists New Posts to read it provides all 2012-2019 3&4 Series without identifying any subgroup where a post may have originated. That’s why I added more specific details.

He was pointing out that the N55 and B58 LSDs are not the same or interchangeable and this is the B58 section.