Turner Custom Limited Slip Differentials - Z4

A custom differential is one of the best upgrades to have done to your BMW. Not only can you get more performance but you can also get rid of the open diff in non M BMWs or M Variable limited slip diff. It's easy to forget about the rear axle when you're considering performance upgrades but changing the gearing is in the top 3 things to do to make the car faster. A custom diff is also a rebuilt unit with new seals, bearings, and limited slip unit.
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E46, Z4 Differential Upgrade - Custom Options
Diffs by Turner - Corporate Logo
T#:340178
Part#: TMS340178
Direct Ship, Expected Ship Date: Oct 7, 2021
Starting at $1,799.00
Free Shipping
Starting at $1,799.00
Free Shipping

One of the best upgrades to be made is custom building a differential. There are a lot of options to make improvements to the diff including gear sizing changes, added limited slip units, and limited slip lock-up options. It's easy to overlook the differential when planning your car's upgrades but it's one of the best areas to get return from your modification spending. Using a shorter (numerically higher) gear ratio will give you better acceleration and the limited slip effect will help get that power to the pavement. Changing the limited slip lock-up will change how the car behaves in corners - low lock-up will introduce more wheel spin; a higher lock-up will give more grip to the rear wheels but may induce an understeer condition (too much power pushing the car straight); a variable lock-up will give you the optimum balance. Our experience in diff building, car prep, and racing will ensure we get you the correct custom build for your specific driving conditions.

Gearing Changes Using a shorter gear ratio (numerically higher) will give you better acceleration but will reduce your top speed. The higher ratio puts you at a higher RPM point for any given speed. This puts you further up in the power band, giving you more torque to the ground. Refer to the chart below for examples.
 

2002 330i, 5-speed manual, 245/40-17" rear tires

(click to expand)

Gear RatioGearSpeedRPM

40 MPH in 4th

2.934th40 MPH2,000 RPM

3.464th40 MPH2,300 RPM

3.914th40 MPH2,600 RPM

70 MPH Cruise

2.935th70 MPH2,800 RPM

3.465th70 MPH3,300 RPM

3.915th71 MPH3,750 RPM

5th Gear Speed @ 6,000 RPM

2.935th151 MPH6,000 RPM

3.465th128 MPH6,000 RPM

3.915th113 MPH6,000 RPM

These are just a range using three gear ratios (stock, middle, extreme). Speeds and RPM will obviously change in between ratios.
Speed in 5th gear at 6,000 RPM is for theoretical and comparison purposes only. It doesn't mean that these speeds are actually reachable.

2005 330i ZHP, 6-speed manual, 255/35-18" rear tires

(click to expand)

Gear RatioGearSpeedRPM

40 MPH in 4th

3.074th40 MPH2,050 RPM

3.464th40 MPH2,300 RPM

3.914th40 MPH2,550 RPM

70 MPH Cruise

3.076th70 MPH2,450 RPM

3.466th70 MPH2,750 RPM

3.916th70 MPH3,150 RPM

5th Gear Speed @ 6,000 RPM

3.075th146 MPH6,000 RPM

3.465th129 MPH6,000 RPM

3.915th114 MPH6,000 RPM

These are just a range using three gear ratios (stock, middle, extreme). Speeds and RPM will obviously change in between ratios.
Speed in 5th gear at 6,000 RPM is for theoretical and comparison purposes only. It doesn't mean that these speeds are actually reachable.


Limited Slip Options. The non-M models of the E46, and Z4 did not come with a limited slip unit. Instead, BMW used either the ASC (Accelerated Slip Control) or DTC (Dynamic Traction Control) to cut engine power, apply the brake(s), or a combination of both. A limited slip operates independently from either of those systems. With the LSD installed the ASC/DTC systems do not engage as often. The LSD transfers torque mechanically to the opposite wheel. It will then allow some wheelspin before the traction control kicks in. If you turn off traction control you still have the torque transfer of the LSD working and then wheel spin. So you can get traction in the corner and some wheelspin out of it to facilitate rotation without engine power being cut by ASC. Our limited slip units are either 2 or 3 clutch 'factory type' units with a pre-set lock-up (usually 40-60%) or the multi-disc OS Giken 0-100% variable lock-up.

Core Charge. If we are building a diff from our own stock a refundable core charge will apply until we get your original diff back. You have a maximum of 30 days from the time you receive the diff to send it back us for a refund. Click here for more detail and explanation of the core charge.

FAQ: For a full FAQ on the custom diff process, click here.

This item fits the following BMWs:
1999-2005 E46 BMW 323i 323ci 325i 325ci 325xi 328i 328ci 330i 330ci 330xii
2003-2008 E85 BMW Z4 2.5i Z4 3.0i Z4 3.0si

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E85/E86 Z4 M Differential Upgrade - Custom Options
Diffs by Turner - Corporate Logo
T#:340225
Part#: TMS21531
In Stock
Starting at $2,249.00
Free Shipping
Starting at $2,249.00
Free Shipping
A custom differential is one of the best upgrades to have done to your Z4 M. Not only can you get more performance but you can also address the weak points in the M Variable limited slip diff. It's easy to forget about the rear axle when you're considering performance upgrades but changing the gearing is in the top 3 things to do to make the car faster. A custom diff is also a rebuilt unit with new seals, bearings, and limited slip unit.

Gearing The MZ4 diff comes with a relatively short 3.62 gear ratio. They could use a shorter gear because the engine redline is so high - the car has a long power band and the gear spacing allows you to stay well within that range. But there's always more acceleration to be had with a shorter gear set. BMW Motorsport supplies 3.91 or 4.10 options and there are other gear ratios to select in our custom builds. Your speed vs RPM obviously changes with a different gear set. Use the chart below for examples of the differences.


Example: 2008 Z4 M, 6-speed manual, 255/40-18" rear tires
(click to expand)
Gear RatioGearSpeedRPM
40 MPH in 4th
3.624th39 MPH2,250 RPM
3.914th40 MPH2,500 RPM
4.104th40 MPH2,625 RPM
70 MPH Cruise
3.626th69 MPH2,750 RPM
3.916th70 MPH3,000 RPM
4.106th70 MPH3,150 RPM
5th Gear Speed at Redline
3.625th171 MPH8,000 RPM
3.915th158 MPH8,000 RPM
4.105th151 MPH8,000 RPM
Why 5th? Because 6th does not have the mechanical advantage to get past wind resistance at these speeds - it is more of a cruise/overdrive gear. Using 5th for comparison purposes is much more relevant than having to take into account wind direction, resistance, grade, elevation, tire sizing, etc. These numbers are for comparisons among gear ratios only, not to determine what your M Coupe will top out at.

Limited Slip Options The M Variable locking differential is genius when it's working properly. Unfortunately, as many M3/M5/M6/Z4M owners have come to find, the system only has a service life of 80,000 miles (sometimes less) and then the viscous unit inside starts to fail (is your's clunking?). We can rebuild the internals and bring it back to a perfectly-functioning viscous M Variable unit. Or you may choose to lose the variable lock in favor of a traditional clutch-type or helical diff with a set locking. We also build diffs with Quiafe, Kaaz, and OS Giken (favorite of the Turner racing team) limited slip units.

Core Charge. If we are building a diff from our own stock a refundable core charge will apply until we get your original diff back. You have a maximum of 30 days from the time you receive the diff to send it back us for a refund. Click here for more detail and explanation of the core charge.

FAQ: For a full FAQ on the custom diff process, click here.

This item fits the following BMWs:
2006-2008 E85 E86 BMW Z4 M Roadster M Coupe
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E89 Z4 35i Manual Limited Slip and Gearing Differential Upgrade
Diffs by Turner - Corporate Logo
T#:340228
Part#: TMS217648
Direct Ship, Expected Ship Date: Oct 7, 2021
Starting at $3,399.00
Free Shipping
Starting at $3,399.00
Free Shipping
Changing the rear gearing on your Z4 35i is one of the best performance upgrades you can make. The shorter gearing will help accelerate the car quicker by placing the engine in the boost sooner for any given speed. Being in that 'meatier' part of the power band means more torque is available at the wheels. Using a shorter (numerically higher) gear ratio will give you better acceleration and the limited slip effect will help get that power to the pavement. Changing the limited slip lock-up will change how the car behaves in corners - low lock-up will introduce more wheel spin; a higher lock-up will give more grip to the rear wheels.

Gearing Changes All Z4 differentials have welded internal pieces that require special machining and modification. Our diff builder has perfected the process and using a shorter 3.46 ring and pinion is now no more difficult than any other car. The stock 3.08 or extra tall 2.81 is offered for rebuilds as well. Using a shorter gear ratio (numerically higher) will give you better acceleration but will reduce your top speed. Refer to the chart below for examples on the difference.

2011 Z4 35i, 6-speed manual, 255/30-19" rear tires
(click to expand)
Gear RatioGearSpeedRPM
40 MPH in 4th
3.084th40 MPH1,973 RPM
3.464th40 MPH2,216 RPM
70 MPH Cruise
3.086th70 MPH2,525 RPM
3.466th70 MPH2,837 RPM
5th Gear Speed @ 6,000 RPM
3.085th145 MPH6,000 RPM
3.465th129 MPH6,000 RPM
Speed in 5th gear at 6,000 RPM is for theoretical and comparison purposes only. It doesn't mean that these speeds are actually reachable.

Limited Slip Options. The Z4 35i sadly did not come with a limited slip unit. Instead, BMW used DTC (Dynamic Traction Control) to cut engine power, apply the brake(s), or a combination of both. A limited slip operates independently from either of those systems. With the LSD installed the DTC system does not engage as often. The LSD transfers torque mechanically to the opposite wheel. It will then allow some wheelspin before the traction control kicks in. If you turn off traction control you still have the torque transfer of the LSD working and then wheel spin. So you can get traction in the corner and some wheelspin out of it to facilitate rotation without engine power being cut so soon. Our limited slip units are either 2 or 3 clutch 'factory type' units with a pre-set lock-up (usually 40-60%) or the multi-disc OS Giken 0-100% variable lock-up.

Core Charge. If we are building a diff from our own stock a refundable core charge will apply until we get your original diff back. You have a maximum of 30 days from the time you receive the diff to send it back us for a refund. Click here for more detail and explanation of the core charge.

FAQ: For a full FAQ on the custom diff process, click here.

This item fits the following BMWs:
2009+ Z4 BMW Z4 sDrive35i
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E46 M3, Z4M Performance Polyurethane Differential Bushing Set
ECS - Corporate Logo
T#:378193
Part#: 002447ECS03KT
In Stock
Sale - Save 20% $130.95
$104.76
Free Shipping
Sale - Save 20% $130.95
$104.76
Free Shipping

Worn rubber differential mounts will lead to the differential twisting and shifting around in the rear subframe. Not only will this be noisy but it's bad for driver confidence and bad for the chassis as well. Even on fresh rubber bushings the differential has deflection and twist, especially if the car has been modified for more torque. Since the differential is centrally mounted in the rear subframe, with all suspension mounts interconnected, a differential with too much deflection will affect handling and could even damage the rear subframe.

These 88A urethane E46 M3 diff mounts are much stiffer than stock but still not as solid as our Turner aluminum/Delrin bushings. This set will resist twisting much better than the stock rubber mounts. Included is the front diff mount and two rear mounts in the cover.

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Powerflex Polyurethane Rear Differential Bushing - E30 E36 318ti Z3
Powerflex - Corporate Logo
T#:376526
Part#: PFR5-300
In Stock
$43.88
Free Shipping

Differential bushings are responsible for keeping the differential in solid alignment while dampening drivetrain vibration. While OE rubber bushings are fine when they are new from the factory, aged and worn out rubber bushings create a multitude of issues that can range from annoying to dangerous. As a factory bushing ages, it begins to harden and become brittle. When this happens the bushing will actually shrink and allow for movement at the differential mounting point. At this point, the differential is free to shift under load causing a noticeable clunking noise under acceleration and deceleration and massively increasing the stress on the driveshaft and axles. Manual transmissions suffer the worst from this as it can make shifting difficult since the differential will shift when the clutch is engaged and disengaged.

By replacing these bushings with full polyurethane, the movement is eliminated since the mounting point is supported by a much stiffer material that will not harden or shrink over time. This means less stress on the driveshaft and axles and greater longevity of supporting components. 

Engineered to perform, Powerflex performance polyurethane differential bushings offer a supreme level of control, while still providing enough comfort for the street, with advanced polyurethane that reduces NVH that often accompanies lesser bushings. Expect improved acceleration response, more direct shifting feel and overall improved drivetrain composure with Powerflex performance polyurethane bushings.

Poweflex is a leading manufacturer of aftermarket suspension bushings. Using state of the art design and manufacturing, all replacement bushings are engineered to out-perform and out-last the ones that came in the car. Each line of bushings is meticulously tested and then re-tested to ensure perfect fitment and enduring quality through the life of the vehicle. A full lifetime warranty backs every one of their products and demonstrates the level of confidence and commitment Powerflex has to their customers. 

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