The S85: the foundation to high displacement, high revving M engines
The S85 was arguably the biggest step up in naturally aspirated engine development for BMW M in its entire history.
Its roots inevitably take us back to the bombastic S72 found in the Mclaren F1. The V12 6.1 engine was fitted with Individual Throttle Bodies, Double Vanos, 4x oil scavenging pumps and came in at 274kg.
It exceeded the legendary threshold of 100hp/liters – an engineering feat on large displacement engines. Even more so using a 10:5 compression ratio.
It did so while using a 86mm bore x 87mm stroke ever so slightly under the square. It pumped out a massive 618hp at 7,400 RPM in 1993
Quite the achievement.
Sounds 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.
Yet, the S85 did with a massively over square engine configuration featuring a 92mm bore x 75.2mm stroke.
The result?
Using the same displacement as the S62 found in the E39 M5, the S85 V10 pumped out an additional 100hp.
It made 500hp revving to 8,250 RPM and generated 384 lbs-ft of torque at 6,100 RPM.
The S85 OEM system: an area of untapped potential
Yet, the S85 was the first of its kind to be fitted to a run-of-the-mill luxury sedan. There were bound to be shortcomings and areas primed for further development.
The intake design was one of them.
High-strung naturally aspirated engines are often already extremely well optimized for airflow in and out of the engine.
The S65 is notorious for this – many companies claimed to get gains from intakes, yet few if 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.
We can now fix this.
Sealed Intake Design: the foundation to power, everywhere, every time.
BMW nailed the S65 intake design and did pretty good with the S85 by using a fully sealed air-intake design with ram air effects 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.
The S65 & S85 engines are both sensitive to IAT (Intake Air Temperatures) and will suffer from heat soak with exposed filter designs.
The sealed configuration is critical to these engines’ performance.
Yet the stock air intake sealed boxes had
shortcomings in their design. The boxes were clunky, and angular, disrupting airflow 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 for emissions purposes.
Optimizing the OEM sealed design with modern-day technology
Technology has moved on since 2004 during the development of the E60 M5.
Today, we’re lucky to have companies like Infinity Auto Design still investing in keeping the S85 relevant, and on the cutting edge of naturally aspirated engine technology.
Infinity revised the sealed intake design by using a double coned filter sandwiched between a lower housing and an upper inlet tube.
There are no rivets, nuts, or screws – just a single clamp.
Control the flow: enhance response & power
The sandwiched filter configuration allows the upper inlet tube to determine the airflow, and not the filter itself.
It reduces the air disruptions and smoothens out airflow, a critical element to improving CFM, and ultimately, throttle response & performance at speeds.
The double coned filter is made from 3x layers of cotton and exclusively made to Infinity Auto Design’s specifications in France.
The upper inlet tube is unique in its design, featuring an integrated MAF housing, unlike other aftermarket intake systems.
The lower housing is designed to fit with the OEM front bumper duct elements, re-using the properly designed aerodynamics from BMW M.
Optimize materials: enhance sound and weight
From my personal experience, the V10 now growls at all RPM ranges. It needs it due to the sound & heat insulation panel under the hood.
The sealed air intakes have a thinner wall construction, enhancing the signature induction noises of the S85.
Infinity’s S85 sealed carbon air intake is the only intake system on the market using a sealed carbon construction. It uses 2x as much carbon as the next best carbon intake on the market.
The carbon process used is the highest of quality: pre-preg carbon cured autoclave.
It is light, strong, and has a signature 2×2 weave pattern.
Unleash the S85
Combining the sealed intakes with DME tuning
I’ve been driving with this combination for a month.
Once you factor in cost, DIY friendliness, and emissions compliance, I believe this is the ultimate bang for your buck performance + driving experience package for S85 V10 on the market today.
Sound, power, efficiencies, laughs, smiles, more fuel stops.
It’s all here.
According to Sal, this is making 540 to 550 at the crank.
I’m clocking 100-200 in the low 8-second range.
Whatever the actual numbers are, the thrills are at peak levels and this is what matters to me in 2022.
I can get ludicrous speeds elsewhere.
There is nothing else like an S85 V10 on caffeine.
Source: Matt@Euroconnex
