I do not know how much of a restriction the MAFS are in the M6's but I do know that in other non-BMW vehicles some decent gains were had with physically removing them from the intake tract. Since the M6 slot-style MAFS are roughly similar shape and size in the intake tract, and the engine requires proportionally more airflow then the others that gained I would figure that something would be gained with the M6 as well, especially considering there are not just one MAFS but two. Will the gain be large? Probably not. But when people fight tooth and nail to even gain 75rwhp from bolt-ons installed in their M6 then 3-5rwhp here and there can add up.
I am an custom ECM tuner so I tend to understand a bit more than the average guy when it comes to the jargon. Every other vehicle I have tuned, the AFR's both at part throttle and at WOT were always more smooth and accurate when the MAFS has been properly recalibrated through the transfer table than any other way such as a speed density mode using MAP or just forcing the vehicle into closed loop all the time. I am not trying to be a naysayer, since I have never tuned an M6 I do not know all of its ins and out's yet. But I would like to better understand the benefits of what you are talking about without you feeling I am asking you to disclose enough information that would be considered intellectual property. So exactly what is allowing it to be more "smooth" because simply stating that it is smoother doesn't really tell anyone much. Is it a WOT AFR thing, PT AFR, Spark advance, transmission shift related or what? When a sensor as important to engine function as the MAFS is removed from the equation I want to know exactly why. I don't mean to come across as challenging or rude, but inquiring minds would prefer more of an explanation than it is smoother and go talk to the E39 guys before dropping their hard earned dollars on this mod.
I will test the restriction for everyone by doing a thorough dyno test with the MAF's in and without by replacing the MAF with a blanking plate/bung.
Will try and measure the pressure drop accross that area with the MAF's removed also.
The cars we are converting to AlphaN already have stage 1 tunes one them so we are not touching the ignition maps between the two versions.
The smoothness does not come from AFR changes. Part load we are always at 1 lambda. Same as with MAF's. The system is in closed loop with or without the MAF's.
Fuel is all target based on the MSS85.
So where does the smoothness come from??
HFM Technology does not measures air mass directly. It is done with the additional input sensors such as barometric and intake air temperature sensors. The output signal is literally just that. An electrical signal. This is used to then calculate a 'load' which is used in variables tables such as fuel.
VANOS and ignition are usually independant of the HFM load calculation.
SO the HFM is really all about trying to make the fuelling as close to maximal efficiency as possible.
However, the setup relies on laminar (smooth) flow through the MAF housing tube so a far more accurate signal may be generated. While in theory on a bench laminar flow may exist, when installed at the beginning of the plenum with pulses being generated through it laminar flow can become turbulent flow at certain loads and engine speeds. Once you get any type of turbulent flow over the HFM the signal becomes distorted.
By removing the HFM altogether (but keeping the IAT sensor) this turbulence is removed leading to improved smoothness.
So now the question comes.... without the HFM we might run into lean or rich conditions under partial load especially.
Well, not really no. First of all we have the closed loop wide band lambda control with the DME being target based.
Then, the fuel maps are very very well developed by BMW and there is also programmed in the throttle position memory of what assumed air mass or load is at any given throttle position. We have barometric and intake temperature correction (so atmospheric) still active.
Now, we are not going to dismiss the MAF completely. They are very useful but really in conditions where for example the air filter becomes extremely blocked or restrcitive and the oil becomes very old and contaminated. Really conditions which the enthusiast is never going to allow. Under these conditions the MAF allows enough correction of fuel injection to get the system to an acceptable emissions level or target.
On the downside the MAF can very easily become contaminated especially when being used with any type of oiled performance (so called) air filter.
Where does this then leave your MAF's as part of an accurate system to control fuel?
What you will tend to find is that if an excellent calibration for fuel is made on AlphaN setup even on cars like the old E30 325i M20 and you just use barometric and intake temperatures for correction, keep the filters and oil clear and don't even use a closed loop lambda system, these cars will run incredibly well and pass tail pipe emissions tests.
So, really, on something as sophisticated as the MSS85 with so much more control and development the MAFs can be taken out of the equation and you have a fantastic running car.
E46 M3, E39 M5's are running evolve AlphaN all over the world with excellent independant feedback and passing emissions at the same time.
The same will happen with the S85.
The assumption here is that owners will avoid any kind of rich running and excellent emissions by keeping clean (ish) air filters and oil.