"In this entry, I document the S65/S85 Manual OE+ Lightweight Flywheel Kit. I touch on the design features, its compatibility with the OE clutch and its benefits." 
- Matt

The GS6-53BZ.

The M5/6 V10 and M3 V8 share the same manual transmission minus a few details. Both are GS6-53BZ. However, the V10's manual transmission made due without an oil cooler due to space constraints. Additionally, the M5/6 V10s had a slightly different and heavier flywheel and matching clutch.. 

I have good news: the differences do not matter in the context of a lightweight flywheel upgrade. 

The OE+ lightweight flywheel. 

The 6spd variant is machine from forged carbon steel just like the DCT. This material is preferred over aluminum for its higher density. As a result, its thermal capacity is uprated and durability is increased. 

OE clutch fitment. 

At the core of our OE+ flywheel design philosophy is the ability to use BMW clutches and retain compatibility with auxiliary components such as throwout bearings, clutch forks, and bolts. 

This provides many benefits: reliability of components, accessibility for replacements and predictability in the driving behaviour.

The last point is arguably most important if you are considering this upgrade. By using OE replacement clutches, the pedal pressure and travel are the same as with the original flywheel - drivability is essentially unchanged. 

The flywheel is designed with the required surface area for the original clutch and the necessary threaded bolt holts and dowel pins to align and install the clutch.

Additionally, the OE clutch for the S65 and S85 were spec'ed by BMW with twin discs - a rather unique choice in BMW M's history. They have continuous organic discs with strap drives to improve smoothness and reduce NVH. They can hold considerable power and make for an ideal street oriented configuration.  

We package our lightweight flywheel clutch kits with OE replacement clutches. Specifically on the S65/85, we use LUKS clutches. The throwout bearing is included along with the flywheel to crankshaft bolts and the pressure plate bolts. 

Reduced weight. 

The single mass design eliminates the dual mass mechanism of the original flywheel on the engine side. Consequently, this is where most of the weight is removed as seen below. 

Due to the transmission and designs differences, the OE+ 6spd manual lightweight flywheel (13.2 lbs) is heavier than the DCT flywheel (11.6 lb). However, the weight delta between the original flywheel (27.5 lbs) is larger leading to more performance benefits in comparaison.

Auxiliary hardware compatibility. 

The flywheel's outer section is machined with a dual teeth outline. The upper section allows the crankshaft position sensor to feed data to the MSS60 to performance its calculations. The lower section is for the engine starter gear.

The starter alignment is validated by aligning the off-round bolt hole on the flywheel with the off-found bolt hole on the crankshaft. 

Additionally, TTV Racing dynamically balances all flywheels in-house. Each hole is carefully machined to a specific depth, shaving off a precise amount of weight.