The M550d Quad-Turbo Insanity

The M550d Quad-Turbo Insanity

0-100 in 4.2 sec with xHP

The M550d G30 has a truly unique drivetrain, that won't be replicated nor matched anywhere in the future. The G30 LCI no longer gets built with this engine. A 3-liter 6-cylinder-diesel with 4 (!) turbos will never be built again, so what we are looking at here is the last of its breed with 400 HP and 760 Nm of torque, straight out of the factory. This power gets matched by the 8HP75 transmission (2nd Generation 8HP), which has a torque limiter in all gears exactly matched to the power of the engine. In other words, proper engine tuning isn't possible, without removing that limiter (Sure, there is some trickery possible around that limiter for engine tuners... but it will never work if done properly).

BMW 550d


But removing a limiter is an easy job, done in seconds, when knowing what to do where. What our maps do and what’s the actual work, is to redesign the character of the transmission and in turn the character of the whole car. To achieve this goal we bought a M550d and used it on an everyday basis for a few months. This is the only way you get to know the small "quirks" every calibration has and understand what the engineers at BMW had in mind when designing the calibration. They do an awesome job in general, but that’s not the point. They have their constraints and many things are done the same way for all models, for various reasons. The calibration for a 530d matches the one for the M550d in many aspects and that is where we can start to go a more specific route and sharpen up the character. The M550d - despite its weight and size - is a very sporty car overall and people buying such a car do have expectations, which might not always get matched by the transmission.

For instance, setting the transmission to S/Sport+ (the most-sporty setting) does not cut it for experienced driving. Downshifting when braking into corners is late (so the engine brake never supports the car's brakes and you are left with a too-high gear on corner exit), blipping is dull and the trans still hurries into the upper gears between corners. It's a bit half-baked and was clearly designed not to upset the people who do not have sport in mind, but just always buy the top-of-the-line model. On our Stage 3 map, there is no more compromise and 3 different mappings can be selected through the DEC (Driving-Experience-Switch) next to the gear-lever. S/Sport+ does the job on its own when going for it, be it on a race track, on the Autobahn, or empty country-side roads. Selecting S/Sport tames down the brake-shifting, softens the blips, does not hold gears for that long, etc. There is now a real difference between those modes.

BMW 550d side view rear


D/Comfort and D/Sport are also redesigned. D/Sport now combines very similar shift points to D/Comfort with a more responsive behavior to quick throttle inputs and harder braking. The trans is easier to sharpen up by shifting or shifting down 2-3 gears, depending on the driver's steering/throttle inputs, but will still use 8th gear when just driving steady. So it’s a true everyday mode, with just a bit of pepper added. This makes room for D/Comfort to be even a bit more relaxed than stock. On mid-throttle, the trans will now shift up earlier for instance, as the massive torque of the M550d easily allows for that. The stock calibration just overdid it a bit in the mid-range. We also overhauled the Launch Control (which resides in the transmission) and achieved a substantial increase of 0.25 seconds over the stock acceleration. Our 2-Ton-Estate-550d now runs a reproducible and steady 4.2x sec from 0-60mph, Youtube) as opposed to 4.45 sec fully stock. Keep in mind, that this is with stock power! The gain is just due to Launch Control adjustments.

BMW 550d side view front


The M550d joined our fleet on November, 20th and after using it for 2-3 months, the actual mapping process started and took around 3 weeks in-car. This included city driving, quick Autobahn runs, and lots of experienced country-road driving. (those poor brakes...) A total of 75 maps were re-calibrated to achieve what we think is a truly unique calibration, clearly different from BMW or Alpina. Of course, many changes don't surface instantly, as they will only show up over time when getting into all the various situations on the road. For example, Eco-Pro now takes off in 2nd gear as standard, we adjusted the nervous downshifting on the slightest incline (something BMW has implemented for ages now), the lock-up clutch of the torque-converter closes a bit tighter, going full-throttle gives you the mathematically correct shift-RPM in each mode, while pressing the kick down releases a few hundred extra RPM, etc., etc. Many of the things mentioned will trickle down to the lower models (530d, 540d, and alike) over the next weeks/months. Sometimes similar, sometimes adjusted to suit the different power bands of those models.

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