Transmission and Drivetrain
The E92 M3 was available with a traditional 3-pedal, manual 6-speed transmission or a 7-speed dual-clutch transmission called DCT. What exactly is DCT? Hint: It’s not an automatic transmission.
Essentially, DCT is an automated manual transmission which uses two separate clutches, one for odd and even gear sets. Almost like two transmissions stuffed into one. A DCT can operate similar to what we think of as a standard automatic transmission, via a gear selector with P-N-D-R. Or in the case of the M3 – gears can be engaged manually via paddle shifters.
It works like this: one clutch has an odd number gear engaged, the computer determines which even number gear will be needed next and ensures the second clutch is ready. Then, it simply switches clutches. FAST. Depending on the shift mode, the DCT can change gears in just 60 milliseconds. The only dual clutch transmission faster than M-DCT was Porsche’s PDK. And we all know how good that is.
The idea behind the innovative DCT was to give M3 owners the ability to drive in an automatic mode, with upshift and downshift settings predetermined in the transmission software, or allow the driver to shift gears as they choose. It is supposed to be the best of both worlds. Unfortunately, the early model M3’s suffered from clunky downshifting and complaints from owners who primarily used their cars in stop-and-go traffic and for general commuting purposes. The good news is the aftermarket can help.
Gearing and Speed Comparisons
Note: The DCT has a 3.154 final drive ratio and the 6MT gets a 3.678.
|Gear||DCT Ratio||DCT Max Speed||DCT RPM on Upshift||6MT Ratio||6MT Max Speed||6MT RPM on Upshift|
Given the engine’s relatively low torque and willingness to produce high RPM’s, the 7-speed DCT makes more efficient use of the S65’s top end powerband. This results in quicker acceleration, better lap times, and something rarely mentioned: increased fuel economy. It’s no surprise that DCT is the preferred choice if lap times are in mind. For those looking to use the E92 M3 primarily as a street car that sees little track use, we recommend the 6-speed manual. But don’t write-off the DCT until you’ve tried it.
Whichever transmission is equipped, power is directed via a 2-piece driveshaft to the rear differential. If DCT, the differential has a 3.154:1 final drive ratio. The 6MT gets a 3.678:1. Whichever the gear set, an Active Variable M Differential Lock providing up to 100% locking action in a completely variable process whenever required and thus ensuring optimum traction on all surfaces. It’s viscous, and does a marvelous job of putting power down. The differential housing uses a unique cover with built-in heat exchangers. As tempting as it may be, don’t use this as a jack point.
Problem Areas and Solutions
The manual transmission can handle plenty of torque. We’ve never heard of a one of these transmissions not being able to take abuse. The DCT transmission does have more components, and more things to go wrong, but failures are rare. Consider either transmission a solid choice.
Improving the Drivetrain
If the E92 M3 is equipped with the dual-clutch transmission, software is available that can help smooth downshifts and make the transmission less clunky when driving around town. Most tuners will provide their custom software that could also optimize launch control and improve upshift and downshift performance.
Final Drive Gear Ratios
Swapping the 6MT’s 3.678 final drive on a DCT equipped car sounds like a no brainer but there have been reports of gear swaps not playing nicely with DCT software. That said, Motorsport24 claims to have a solution for DCT owners.
3-pedal owners, there are a number of final drive ratios available ranging from 4.10 to 5.44. Motorsport24 offers those as well.
The Good and Bad
|Transmissions can take plenty of torque||DCT can be clunky around town|
|Active M Limited Slip Differential||DCT software doesn’t like FD changes|
|DCT can upshift in 60ms||–|