Unfortunately, the 135i and 335i powered by the N54 received open differentials from BMW. It's a serious limiting factor for those looking to make more power and/or track their cars. A limited slip differential is an excellent mod to help put more power down. In this guide, we will discuss limited slip differentials and list a few popular options on the market.
N54 Open Differential - Why is it Bad?
One of the biggest misconceptions with open differentials is that they send more power to the wheel with the least traction. That is not true. With an open differential neither drive wheel gets more torque. Ever. Each wheel receives exactly 50% of the torque at all times. However, the torque is limited by the wheel with the least traction.
For example, your N54 might have up to 500 torque at the wheels. If one tire begins losing traction then friction decreases and the tire spins easier. Let's further assume the tire losing traction only needs 150 torque. Therefore, the differential will limit the torque going to that wheel to 150 lb/ft. That's where the problems begin with an N54 open differential. Again, each wheel is always receiving 50% of the torque. If torque is limited on the wheel with less traction then it's limited at both wheels. The wheel with perfect traction also only receives 150 torque even though it might have enough traction to handle the full 250 torque. Enter a limited slip differential (LSD).
What is a Limited Slip Differential?
Unlike open differentials, limited slip differentials can vary the torque to each wheel. Generally, an N54 LSD can send up to roughly 70% of the torque to the wheel with the most traction. Let's circle back to the previous example. One wheel only requires 150 torque before losing traction. That's 30% of the 500 torque. The limited slip differential will then send up to 350 torque (70%) to the wheel with more traction. Assuming it has the traction to put down the full 350 torque then you actually still have a usable 500 torque. In this situation, the stock 135i and 335i open differential would only be capable of putting 300 torque to the ground.
In a straight line on a well prepped track it's likely both tires will have about the same traction. However, even then it's not always true. If you're the only one in the car then there will be more weight on the driver side. On the streets it's even less likely each wheel has the same traction. There may be sections of pollen, oil spills, leaves, bumps, uneven roads, etc that limit the traction capabilities of only one wheel. Finally, cornering is a major area where each wheel has very different traction capabilities. As the weight sinks to one side of the vehicle it helps the tire with more weight. However, the tire on the opposite side receives significantly less weight. That tire is going to spin easier.
The point is - the two drive tires rarely have the same amount of traction capabilities. An LSD is designed to put as much torque down as possible in any given situation. It sends more torque to the wheel with better grip and less torque to the wheel losing grip.
1.0 vs 1.5 vs 2.0 Way Limited Slip Differentials
We want to avoid getting too technical in this post and our explanation wouldn't be as good. As such, we highly recommend checking out this YouTube video if you're interested in learning about the differences.
Different N54 135i 335i Factory Differentials
Before diving into upgrades it's important to understand which factory differential you have. They're all open differentials, however there are some other differences. Some N54 powered 135i and 335i models received a bolted diff while others were welded. This is the general guideline for bolted versus welded N54 differentials:
- 335i auto trans. (up to 02/2007) - BOLTED
- 335i auto trans. (03/2007 to 09/2007) - WELDED
- 335i auto trans. (10/2007 to end of production) - BOLTED
- 335i manual trans. (up to 02/2007) - BOLTED
- 335i manual trans. (03/2007 to end of production) - WELDED
**The A/T 335i differentials are questionable. Some claim ALL N54 335i models have a bolted differential. A few had 03 and 04 2007 production 335i's with bolted differentials. The above list is generally correct. However, if you're in the grey area of 03/2007 to 09/2007 the only way to know for sure may be to actually open up the differential).
- 135i auto trans. (ALL) - BOLTED
- 135i manual trans. (ALL) - WELDED
Why Do Bolted vs Welded N54 Differentials Matter?
N54's with a bolted differential can simply swap the rear open diff for a LSD. Welded differentials add some complications that ultimately make the upgrade more expensive. It's an unfortunate reality for some of us (our 335i A/T has an 04/07 build date). However, those with welded differentials still have solid options. Often this includes receiving a new pumpkin (typically rebuilt) which includes the pre-installed LSD.
You could also have the pumpkin machined to accept an LSD on your own. However, it requires a capable shop to complete a job like this. It's usually easiest for most to opt for a new pumpkin with the LSD already installed.
Best N54 135i 335i LSD's
Alright, enough with the boring information. Once you understand whether your N54 differential is bolted or welded it's time to decide what the best upgrade is for you. In this section, we'll list out a few of the best N54 135/335i differentials. Please verify fitment for your vehicle specifically. Some links may direct you to automatic transmission parts even though it may be available for auto or manuals, for example.
Best Limited Slip Differentials - Bolted Only
The below options are differentials only. These options do NOT include the pumpkin, so they will not suffice for welded N54 differentials. Again, you could have your factory welded differential machined to accept the bolted LSD's. However, we do not recommend this option.
1. MFactory Helical Limited Slip Differential
One thing we skipped over in this post is helical vs metal plate limited slip differentials. A helical LSD is typically the best all around differential for straight line and cornering performance. Helical differentials allow for different wheel spin rates - just like an open differential. For example, when cornering the outside wheel has a greater distance to travel. Therefore, the wheel spin rate is faster than the inside wheel. A helical limited slip differential allows different spin rates while still varying torque to the wheel with better traction.
This is one of the most common LSD options for the N54. If you're in the fortunate group with a bolted differential we highly recommend this option. MFactory makes some excellent LSD's for a great price.
Buy Here: MFactory Helical LSD N54 135i 335i
2. MFactory Metal Plate Limited Slip Differential
Metal plate differentials act a bit more like locked differentials. They do not allow for varying wheel speeds so they're typically best suited to straight-line applications. As we mentioned with the N54 MFactory Helical LSD - when cornering the outside wheel travels a greater distance. Since wheel speeds are locked it will partially "drag" one wheel around the corner. However, as with all LSD designs, they vary torque to each wheel depending on traction.
The MFactory Metal Plate differential is available in 1.0 way, 1.5 way, or 2.0 way. Again, the link we provided earlier in the article is a great explanation of the differences. Ultimately, the 135i and 335i metal plate differentials should be limited to those primarily looking for straight line performance. We highly recommend the helical LSD's for the all around balance of straight line, cornering, and daily driving.
Buy Here: MFactory Metal Plate LSD N54 135i 335i
Best Limited Slip Differentials - Full Pumpkin
These are all great options for anyone with a welded differential. Many include core charges so you will need to send in your OE differential once the new one is installed (assuming you want your core deposit back). Those with bolted differentials may also opt for a new pumpkin.
1. MFactory Pumpkin with Helical LSD
This complete unit is set for a simple bolt-on replacement. Remove your entire differential and pumpkin and simply bolt this one up. It's the exact same limited slip differential as mentioned in the previous section. The difference being this pumpkin was machined to accept the limited slip differential.
Again, we believe the MFactory Helical LSD is one of the best options for N54 powered 135 and 335i's. Note - the price includes the $500 refundable core charge. Send in your old unit and get $500 back.
Price: $2149.96 ($1649.96 if you return your old part)
**Please note - manual transmissions came with a 3.08 final drive while automatics came with the 3.46. They are interchangeable.
2. WaveTrac Limited Slip Differential
This option is available as a standard limited slip differential only or with the entire pumpkin. It's more or less the same option as above simply a different brand. The differential only comes in at $1,295 while the pumpkin and LSD are $2,744. The pumpkins price includes an $800 refundable core charge. As such, if you send in your old pumpkin the price effectively drops to $1,944.
This is another popular and excellent option all around. It's a little pricier than the MFactory differentials, but the quality is also excellent.
Price: $2,744 ($1,944 if you return old pumpkin)
Buy Here: WaveTrac Pumpkin & LSD N54 135i 335i
3. VAC Performance Built Rear Differentials
This option from VAC Motorsports is a bit pricier, but the customization options are excellent. First, you may choose between WaveTrac, Quaife, OS Giken Superlock, or OS Giken T.C.D. limited slip differentials. All excellent LSD's. Then you can opt to send in your pumpkin housing up-front for them to build out, receive a "good used" housing, or a brand new housing. Finally, you can choose either the standard differential cover or a billet finned option.
All of these options come with brand new hardware, gaskets, seals, etc. These are basically fully rebuilt units featuring limited slip differentials. If you opt for the brand new housing then you're getting completely brand new components from top to bottom. Prices start at $2,249.95 and go up depending on your options. Definitely not the cheapest, but these are certainly some excellent rear differentials.
BMW N54 135i 335i LSD Summary
There's a lot that goes into rear differentials overall. We wish we could cover more but the post would simply be too long. Hopefully we provided a good starting point in deciding which differential may best suit your needs. In summary, the open differentials on the N54 135i and 335i are shortcomings that greatly limit traction capabilities. Limited slip diffs are a great mod to help put as much power to the ground as possible.
There are many differences in LSD's such as helical vs metal plate, 1.0 way vs 1.5 way, etc. Ultimately, we believe helical limited slip differentials are the best option for most N54 owners. They provide an excellent balance of straight line and cornering grip.
Lastly, it's important to understand whether you have a bolted or welded differential prior to upgrading. Those with bolted differentials may simply upgrade to the limited slip differential alone. However, those with welded differentials are likely best opting for a full pumpkin.