"These build journal entries are part of a Special Series on the development of the S85 CSL Style Carbon Plenum and S85 CSL Competition Complete Carbon Intake System.

In this entry, we're discussing the technical specifications of S85 Competition Carbon Plenum in collaboration with Salman, head product designer at Infinity."
- Matt

Keyword: modular.

Why does being modular matter?

The S85B55 & S85B50 were designed with individual throttle bodies at an angle of 120 degrees - unlike its littler brother, the S65B40, that has a 180 degrees, flat individual throttle body design. 

The S85B50. 

The S65B40. 

It was just a prototype!

BMW M engineered the prototype CSL intake as just that - a prototype. The engineering restrictions for ease of access and maintenance by dealerships was not a concern. 

Fitting a 1 piece plenum over 120 degrees ITBs would result in an extremely high rate of installation errors leading to engine power limiting errors. 

It would also potentially lead to damages to the carbon plenum considering the tight spaces within the engine bay and the enlarged dimensions of the 1 piece plenum. 

The modular specs.

The ITBs bosses are attached separately from the plenum base directly on the ITBs. This allows you to easily position the carbon base over them prior to fitting the velocity stacks. 

The upper cover of the plenum is designed to be fitted with bolts to the carbon base. The ability to remove the upper cover is key to making the whole modular design work. It gives you access to the velocity stacks. 

Individually removable velocity stacks

You guessed it, the velocity stacks are indeed removable and modular. The current velocity stacks are designed to mimic the OEM dimensions. 

More designs will be made available in the future along with documented R&D notes to show the varying performance gains. 

One Piece Velocity Stack designed with flanges

The velocity stacks have flanges that enable you to directly bolt the stacks to throttle body bosses. This is key to avoid common causes of carbon fiber trumpet failures.

Larger side inlets

The larger inlets are designed to resemble the M5 CSL prototype. Along with the increase carbon volume, this is another key to allowing more air to flow into the S85. 

Modular inlet ducts

The side inlets connecting to the dual air boxes are modular. An OEM sized inlet is available and designed for fitment with OEM MAF to retain a stock-like tune.

Optionally, you can opt for larger diameter inlet ducts to mimic the BMW M5 CLS prototype. These require Alpha N tuning and to be paired with the soon-to-be-released larger diameter inlet tubes on the S85 Sealed Carbon Intakes.

A complete plenum, intake and Alpha N tuning package will be made available during introduction.  

Up next: we will explore the test fitment of the 3D printed prototype and initial impressions of the carbon prototype of the S85 CSL Style Carbon Plenum.