Why BMW M sealed their intakes.

Why BMW M sealed their intakes.

"These build journal entries are part of a special series on the development of the E60 M5 & E63 M6 sealed carbon intakes and written in collaboration with Sal at Infinity Design.

In this journal entry, I cover the historical foundation to the sealed intake designs of BMW M."
- Matt

They collaborated with the best of them. 

The bombastic S72 found in the Mclaren F1 was a BMW Motorsport creation. It exceeded the legendary threshold of 100hp/liters - an engineering feat on large displacement engines.  

It pumped out a massive 618hp at 7,400 RPM in 1993.  Even more so using a 10:5 compression ratio and an under-square engine design with its 86mm bore x 87mm stroke. 

The V12 6.1 engine was fitted with Individual Throttle Bodies, Double Vanos, 4x oil scavenging pumps and came in at 274kg. 

It made use of a sealed intake design connected to the roof air ram. It was cleverly designed by Gordon Murray to enhance performance & the aural dimension of the driving experience. 

Sounds somewhat familiar.

The V10 in the M5 had Double Vanos, Individual Throttle Bodies, Quasi-Dry Sump with secondary oil scavenging pumps came and in at 240kg. 

It was engineered with a vastly different core design philosophy versus the S72: the S85 was a massively over square square engine configuration featuring a 92mm bore x 75.2mm stroke. 

 

The S85 was arguably the biggest step up in naturally aspirated engine development for BMW M in its entire history. 

It made 500hp revving to 8,250 RPM and generated 384 lbs ft of torque at 6,100 RPM uing the same displacement as the S62 found in the E39 M5, the S85 V10 pumped out an additional 100hp. 

The S85 OE Sealed Intake. 

They still did pretty good with the S85 by using a fully sealed air intake design with ram air affects from the front bumper. 

The S85 air intakes are fed from 2x ducts in the front bumper to maximize the ram air effect at speeds. Anyone who has owned or driven an S85 knows what I mean: once you get into 4th gear at WOT, it feels like you added 2 cylinders to the V10. 

It's part of the recipe to make the BMW M with the highest top speed ever recorded - to this day. 

 

Temperature-Sensitive.  

The sealed configuration is critical to these engines performance.

The S65 & S85 engines are both sensitive to IAT (Intake Air Temperatures) and will suffer from heat soak with exposed filter designs. 

Yet the stock air intake sealed boxes had short comings in their design. The boxes were clunky, and angular, disrupting air flow critical to making optimal power at speed.

The OEM paper filter was a further restricting point. The North American S85s also had a secondary charcoal filter from emissions purposes. 

 

BMW M mastered it with the S65 V8. 

High strung naturally aspirated engines are often already extremely well optimized for air flow in and out of the engine.

The S65 is notorious for this - many companies claimed to get gains from intakes, yet few of any actually did. BMW M optimized the air intake system and simply nailed it.

It pumped out an impressive 105PS per liter, about 5% over the V10. 

With time comes improvements, and BMW M unfortunately never released the mythical 1 piece carbon airbox and enlarged intake designs of the prototype M5 CS.

The S85 was the first of its kind to be fitted to a run-of-the-mill luxury sedan. There were bounds to be shortcomings and areas left with untapped potential. 

Up next: I unbox Infinity's sealed carbon intakes and dive into its technical specifications. 


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