Quote:
Originally Posted by E90convert
The the electronic LSD, the calibration is specific to the BMW/Castrol oil. So using something different may result less than optimized differential performance in all operating conditions.
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This is untrue for so many reasons:
1) The actual OEM fluid for these differentials isn't castrol's/bmw's SAF-XJ, it's actually BMW's MSP/A, and MSP/A is unlikely to be a Castrol product (I believe Castrol I'm Germany is based in Hamburg, while MSP/A is made in Munich). The only country that uses SAF-XJ is the USA (well Canada will soon move over to SAF-XJ too, because of logistics but when I changed my diff oil in 2020 and 2016 I was given MSP/A).
2) ISTA specifies bmw approved differential oils, and liquimoly among others were approved as suitable replacements for bmw's diff oil.
3) the differential isn't as tunable as you think it is, the 2 servos are driven by a pwm signal. The higher the pwm the more force the servos put onto the clutch packs which locks the rear axles tighter. This tuning is quite granular and not based on 1% increases in pwm (because the changes in clamping forces is way too small to make a difference). Instead the pwm changes is likely in the 5%, 10%, 25% increments. What really makes the tuning work is how these servos respond to yaw angle, and wheel speed - pretty much the dsc and stability control system. Then it determines if it wants more wheel lock or not, and if it still needs more wheel lock itll request more pwm from the servos. In addition to that it can apply that pwm to the left or right wheel independently to vector torque. The ghas coding likely helps it determine how agressive it vectors torque. So pretty much it's the car's vehicle dynamics tuning that determines how much the diff engages and if it needs to engage more to meet targets (yaw and wheel speed), the diff itself is pretty granular in terms of tuning (pwm and left or right).
So the idea that it's calibrated only for the Castrol/BMW oil is absurd.
Quote:
Originally Posted by E90convert
I’d bet the MTF-LT-5 will handle heat just as well as any other PAO synthetic. It’s the gears, bearings, and seals that are the question! I’m sure they are fine, it’s designed and for that oil viscosity. The transmission doesn’t get that hot on an M2 either, and the thin oil helps keep the temps lower.
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I doubt it, bmw oem fluids are designed to meet 2 main things: oxidation resistance to last "a lifetime", and low viscosity (mtf from bmw is super thin) to reduce drivetrain losses and meet emissions targets. This means they're not going to be able to bring a lot of Pao's and esters to the mix because it will break down too fast to be a "lifetime fluid", and so they have to use more group 3 oils. We know for a fact esters and Pao oils tolerate heat way better than group 3 oils, so there is no way bmw's mtf is going to tolerate heat better than something like a redline dctf which is all esters and Pao's.
The transmission may be designed for that oil viscosity, but that doesn't say anything about sheering and viscosity decreases due to heat.
What is your proof the 6mt doesn't get hot on the m2? Have you ever done an oil change on it before? Because I have and it gets unbelievably hot even with just city driving for an hour I can barely touch the transmission case. When I drained the oil itself, that was after jacking up the car, and doing an oil change so ~1hr total before I drained the mtf, and it was still as hot as a cup of coffee. You get from the store.
So im willing to say when on track that mtf is easily exceeding 100C.