E46, Z4 Differential Upgrade - Custom Options

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

T#: 340178 | Part#: TMS340178
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No REM Bearing Polish.
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E46, Z4 Differential Upgrade - Custom Options
$1805.95