Where improving upon M is actually hard.

Where improving upon M is actually hard.

"In this new Special Series, I document the latest S65 Upsized & Sealed Carbon Intake: I go through its development, technical specifications, driving impressions and real world results. 

In this entry, I touch on the engineering prowess of BMW M in their design of the S65's air intake system and why aftermarket options were a nice-to-have, and not a must-have, until now. I discuss the development focus of the new S65 Upsized & Sealed Carbon Intake."
- Matt

Sealed intakes are the only way.

In 2021, I discussed the origins and merits of BMW M's sealed intake design on the S85 and their further evolution on the S65 in "Why BMW M sealed their intakes".

The answer can be generalized to a single metric: air intake temperature. 

In simple terms, cooler air is denser air, and denser air allows more power to be made, and power to be sustained during high RPM operations. 

BMW M's naturally aspirated, high revving are extremely sensitive to this specific temperature change. We can't adjust boost to compensate, we can only lose power.

BMW M understood managing intake air temperatures as a critical component of their design evolution from the S85 to the S65, implementing two main changes: software and design. 

Winter time dynos always produce higher numbers. Honest companies will present the weather and elevation adjusted numbers. 

AlphaN engine management protocols. 

BMW M ditched the S85's Mass Air Flow (MAF) sensors and switched to a AlphaN engine protocol for the S65.

It uses different data inputs and sensors: Mass Air Pressure (MAP) and Intake Air Temperature (IAT) to manage ignition, fuel trims and other variables under load. In short, absolute air pressure and the air's temperature drive the performance of the engine. 

The software change opened up new design possibilities for BMW M leading to a completely redesigned air intake system for the S65.

The S85 originally used 2x Mass Air Flow sensors located at the outlet of the original plastic air filter boxes. 

The S65 uses an IAT at the plenum's inlet.
The MAP sensor located on the back of the bank 2, driver side rail. If it fails, this is knuckle scratching DIY. 

For more information on MAF, MAP and Alpha, you can read my entry "Alpha V10"

Air Intake Design Optimization. 

The S85's MAF sensors restricted the intakes leading to the plenums within specific dimensions and shape to achieve a stable air flow reading. It forced BMW M engineers to design a dual plenum system to individually manage the air intake per bank.

The S65's AlphaN protocols impose no such limitations: it could have any varying shape. 

This is most evident with design of the plenum: it is now a single piece plenum with a singular intake tract. BMW M further maximized the available engine bay space by increasing the air filter box dimensions, and enlarging the intake leading to the plenum. 

The S65's elbow has a varying shape throughout the air tract. 

Heat extraction. 

BMW M notably added vents to the V8s hood, with only the driver side being functional. The vents are often misunderstood: they do not drive cold air in, they extract hot air.

The purpose is to limit turbulence and accelerate air flow in the airbox. It is achieved by allowing the less dense, hotter air to espace the air box through the extractor, leaving colder air to enter the engine. 

The vents and powerdome are signature, functional design elements of the M3 V8. 

The kidney grills are connected to the air filter box by a 2 piece air duct on top of the radiator, going through the carrier. The ducting further drives cold air into the box. 

The driver side bumper opening drives air directly into the air filter box via a sealed duct. 

How do you improve upon this?

It is extremely difficult to objectively improve upon the original design with any meaningful, measurable success. Many after aftermarket companies attempted to improve upon the system.

Most attempts can be framed within these variables:

  1. Material change: 

    Carbon is often selected for its thinner construction, allowing more induction noise and improvement to engine bay aesthetics. 

  2. Design optimization:

    The elbow is smoothen out with claims of single digit horsepower gains.

  3. Filter material:

    Some companies use their own filters and opt for oiled units. Due to slightly lesser filtration, gains can be achieved. 

  4. Filter design:

    Some improve the surface area and shape of filters, notably conic designs. They usually lead to designs making away of the lid, using the aluminum hood instead. This is problematic for IATs. 

  5. Dimensional increases:

    The carbon plenum can be slightly enlarged, but it is physically limited by the power dome's hood clearances. Such plenums may easily rub against the aluminum strut bars due to lower tolerances. 

Ultimately, none of of these add up to meaningful gains beyond questionable dyno sheets and 100-200 times with considerable negative slope differences. 

In consideration, performance oriented intake upgrades have not been my priority on the S65 over my other M cars. I have been happy with S65 carbon plenums for their impact on induction noise and engine bay aesthetics.

They're a great smile per mile upgrade with limitless customization options. 

In 2023, the need for more arose. 

In 2023, I set out to empirically prove, or disprove an hypothesis: could we reach 125hp/liters on naturally aspirated, stock displacements S54, S65 and S85 engines?

The Sxx-EVO high duration camshaft programs begun development with the S85B50.

The fundamental approach of the Sxx-EVO program is to maximize the intake and exhaust duration of the camshafts compatible with BMW M's dual VANOS systems. 

The underlying approach is make optimal use of the available air volume of enlarged intake systems and the increased flow of enhanced aftermarket exhaust systems to rev higher. 

In short: we succeeded. 

Maximizing the air volume is a critical component in unlocking performance at higher RPMs in the S85-EVO Program as is evident by the Mustang dyno results below. 

The S85-EVO uses the CSL Competition Intake System with an enlarged, single plenum design with space maximized intake inlets and sealed lower housings. 

The V8 is a different beast. 

In the Spring of 2024, we started road and dyno testing of the S65-EVO high duration camshaft program. 

The exhaust component. 

BMW M further refined the S65's exhaust design by featuring equal length headers with its primary catalytic converters moved to the section 1 system for optimal merge collector design. 

I have the Akrapovic EVO system fitted with it's 2x100 CPSI catalytic converters to optimize the remainder of exhaust pathways. 

The headers hiding under the heat shields. Shame, they are truly works of art. 

The intake component. 

Upon reviewing dyno numbers from the first tuning session, we analyzed cam timing numbers and felt there was more potential to be found on the intake side. 

Considering the exhaust side was optimized, the next focus to enhance the S65-EVO was to increase air volume as proven effective on the S85-EVO. Few quality carbon options were available on the market to improve upon the OEM air intake. 

The only available option at the time was the M3 V8 Karbonius complete carbon intake kit

It's the most massive plenum on the market, maximizing engine bay and hood clearances. It is unfortunately restricted by the elbow, and most critically, the air filter box design.  

We had to go beyond the box. 

Ever since the initial market entry of Infinity Design with the S85 carbon intakes, we had been discussing ways to bring an innovative S65 solution to market.

The design team scanned, digitally simulated air flow and analyzed potential improvements to the OEM plenum and air intake. 

The original plenum is very well designed. It presents some improvement possibilities in regards to overall volume as achieved by other companies on the market. 

A core focus. 

As previously discussed, the current aftermarket elbow designs are ultimately limited by the available space between the plenum's inlet, and the original air filter box. 

From a cost/benefit/market analysis, we isolated the elbow and the air filter box as the most probable area of improvement.

The design team begun development of the first designs by approaching the S65 at a new angle. They opted to redesign the complete air intake tract from the plenum as a single unit, with a focus around maximizing its core: the air filter.

A rough render was released in 2022 showing the filter at the core.


The render showed promises of the largest cone filter ever fitted to the S65 by enlarging and extending the elbow design into a completely new air filter box. 


The design still kept the fundamental cold/hot air circulation of BMW M's engineer by retaining the 2x cold air ducts, and the heat extractor.

Following the released of the S85 CSL Competition intake, the S65 design was revised, refined and enhanced in 2023. 

The elbow was further extended and enlarged, maximizing the available space in the chassis while still retaining BMW M's sealed and ducted air filter box concept. 


In 2024, it was time to go from virtual to reality. The molds were put into production and the first prototypes were delivered. 

Up next: I get my hands on a production unit of the S65 Upsized & Sealed Carbon Air Intake

I will document its features and review it against the original airbox before being installed and tested on the S65-EVO. 

Leave a comment

Please note, comments must be approved before they are published

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

The latest entries to the Stripper's build journal

m3 v8 programs
I source what I document.