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So much forum confusion about alpha-n tunes vs csl tunes
- Thread starter Sajk
- Start date
pokeybritches
Member
Let me blow your mind for a minute. All Z4M MAF-based tunes still use alpha-n. The MAF sensor can't respond quickly enough to rapid changes in airflow, so the ECU momentarily reverts to alpha-n until the MAF can catch up. Unfortunately most tuners don't touch the alpha-n tables with MAF-based tunes, and I would venture to say that most aren't familiar enough with the ECU to understand what it's doing. This leads to the perception of lag with the MAF tune, but in reality it's because the tune isn't optimized. It becomes more apparent with engine modifications.
I wrote a long post about alpha-n vs MAF previously, so I won't fully rehash what I've already said. In summary, MAF is better in most cases. However, a fully optimized alpha-n tune should behave like stock. Many times sensor scaling is misunderstood or ignored, and that leads to some of the problems others have mentioned with alpha-n. I would take an MSS70 alpha-n tune over a MSS54 MAF tune on any naturally aspirated or supercharged setup, due to the MSS70's wideband sensors. While the ECU "guesses" airflow with alpha-n, the MSS70's wideband oxygen sensors will tell you what the actual mixture was. The ECU trims fuel to correct.
Martyn's info is on point. MSS70 does have a built-in baro sensor. Tunes that don't perform as well at altitude are likely suffering due to the ECU operating in a different part of the fueling map which isn't typically tuned at sea level on the dyno. I have not heard of melted pistons in a naturally aspirated S54. The S54 is very robust. You wouldn't believe some of the tunes I've come across... knock thresholds raised to the moon, 16+ deg of ignition timing beyond stock with 98RON tables copied over to 91RON, on cars that are driven hard in the Middle East. I couldn't have come up with a worse tune if I was intentionally trying to blow up an S54, yet the engine endured and still put down fantastic numbers when properly tuned.
The car exhibited a hiccup with both Epic's tune and my tune, which would lead me to believe it was hardware-related, since the airbox was the commonality with both tunes. Most alpha-n Z4Ms don't have hiccups, and it wasn't showing in data logs. MSS70 is sensitive to brake booster faults, and the modifications to support the carbon airboxes can cause hiccups. FWIW, the Epic canned map did cost more than the Severn custom map, and we also provided the MAF-based tune for no additional charge once the car's direction changed.
OEMs don't do nearly the performance calibration work that we're led to believe, and they are bound by emissions standards. I'm fortunate to be one of the few to acquire the official Siemens documentation on MSS70, which is very rare, over 6000 pages long and describes how the ECU works. Additionally, I have a (more common) A2L file which details the addresses of all 8000 parameters in MSS70. I don't think BMW has any one single engineer that is fully familiar with MSS70, because the parameters look like they were decided upon by committee. Some sections that should be minimally relevant are overly complex- like an engineering team was seeking job validation or something to brag about to their customer- while other very important areas are only briefly covered. These files paint an interesting story. Nonetheless, it does take a lot of time to figure out MSS70, even with all the documentation. Much of it is not documented in the way we would like.
I wrote a long post about alpha-n vs MAF previously, so I won't fully rehash what I've already said. In summary, MAF is better in most cases. However, a fully optimized alpha-n tune should behave like stock. Many times sensor scaling is misunderstood or ignored, and that leads to some of the problems others have mentioned with alpha-n. I would take an MSS70 alpha-n tune over a MSS54 MAF tune on any naturally aspirated or supercharged setup, due to the MSS70's wideband sensors. While the ECU "guesses" airflow with alpha-n, the MSS70's wideband oxygen sensors will tell you what the actual mixture was. The ECU trims fuel to correct.
Martyn's info is on point. MSS70 does have a built-in baro sensor. Tunes that don't perform as well at altitude are likely suffering due to the ECU operating in a different part of the fueling map which isn't typically tuned at sea level on the dyno. I have not heard of melted pistons in a naturally aspirated S54. The S54 is very robust. You wouldn't believe some of the tunes I've come across... knock thresholds raised to the moon, 16+ deg of ignition timing beyond stock with 98RON tables copied over to 91RON, on cars that are driven hard in the Middle East. I couldn't have come up with a worse tune if I was intentionally trying to blow up an S54, yet the engine endured and still put down fantastic numbers when properly tuned.
maupineda said:
The car exhibited a hiccup with both Epic's tune and my tune, which would lead me to believe it was hardware-related, since the airbox was the commonality with both tunes. Most alpha-n Z4Ms don't have hiccups, and it wasn't showing in data logs. MSS70 is sensitive to brake booster faults, and the modifications to support the carbon airboxes can cause hiccups. FWIW, the Epic canned map did cost more than the Severn custom map, and we also provided the MAF-based tune for no additional charge once the car's direction changed.
maupineda said:
OEMs don't do nearly the performance calibration work that we're led to believe, and they are bound by emissions standards. I'm fortunate to be one of the few to acquire the official Siemens documentation on MSS70, which is very rare, over 6000 pages long and describes how the ECU works. Additionally, I have a (more common) A2L file which details the addresses of all 8000 parameters in MSS70. I don't think BMW has any one single engineer that is fully familiar with MSS70, because the parameters look like they were decided upon by committee. Some sections that should be minimally relevant are overly complex- like an engineering team was seeking job validation or something to brag about to their customer- while other very important areas are only briefly covered. These files paint an interesting story. Nonetheless, it does take a lot of time to figure out MSS70, even with all the documentation. Much of it is not documented in the way we would like.
pokeybritches
Member
Vanne said:
I was looking into it, but I don't think the ECU has the logic to use a MAP like the E46 M3 CSL. I haven't found anything in the ECU's documentation mentions it, and it only seems to be referenced in the parameter section of the ECU's file. It would be nice if it was as simple as flipping a digital switch to turn it on, but I don't think that's the case.
I could use a beer or two :rofl: When are you coming out this way??
pokeybritches
Member
Sajk said:
I know a guy- me
Feel free to send me a PM.I can say Josh’s tunes are really good. I am in Mexico City and we have 2,400m above sea level, or almost 7900 ft. . My tune is optimized for sea level but I drove it this past week in Mexico city and the car ran perfect, i always feel the effect of elevation in the engine’s performance but that is expected at such altitude which means 24% less power 
@pokeybritches, interesting your thought on my issue being hardware related, the MAF based tune has totally fixed the hiccups I had, I wonder if the hardware issue was the shut off valve, or the airbox itself. The car always had a vacuum dtc but there were no leaks, though we know the seal between the two halves of the CSL airbox is far from being air tight. So It could be the shutoff solenoid valve. With the MAF, Eventuri and Karb box is really smooth and hiccups free.
@pokeybritches, interesting your thought on my issue being hardware related, the MAF based tune has totally fixed the hiccups I had, I wonder if the hardware issue was the shut off valve, or the airbox itself. The car always had a vacuum dtc but there were no leaks, though we know the seal between the two halves of the CSL airbox is far from being air tight. So It could be the shutoff solenoid valve. With the MAF, Eventuri and Karb box is really smooth and hiccups free.
maupineda said:I can say Josh’s tunes are really good. I am in Mexico City and we have 2,400m above sea level, or almost 7900 ft. . My tune is optimized for sea level but I drove it this past week in Mexico city and the car ran perfect, i always feel the effect of elevation in the engine’s performance but that is expected at such altitude which means 24% less power
@pokeybritches, interesting your thought on my issue being hardware related, the MAF based tune has totally fixed the hiccups I had, I wonder if the hardware issue was the shut off valve, or the airbox itself. The car always had a vacuum dtc but there were no leaks, though we know the seal between the two halves of the CSL airbox is far from being air tight. So It could be the shutoff solenoid valve. With the MAF, Eventuri and Karb box is really smooth and hiccups free.
At least on the CSL, a leak at the airbox will not cause a DTC. It sounds like you might have an issue with one of the vacuum lines and the MAF is compensating for a hardware issue. The ECU has the baro pressure sensor, so altitude should not be your problem. Any combustion engine will lose power at that altitude change.
just-right
Member
An interesting topic. A lot of the older racing engines are running pure alpha (throttle position) and n (engine rpm) For almost all engines this is still the base table with a considerable addition of sensors to aid fueling and ignition adjustments.
The lambda sensor will give you a reading of oxygen content and therefore the air fuel mixture. Based on the injected fuel this will allow the ecu to calculate the air and thus load on the engine. Depending on the position of the sensor and response time there will typically be some lag.
A MAF or MAP sensor will allow a much more direct measure of load on the engine. On the CSL the MAP sensor should be measuring behind the throttle plates and thus have more variation in static pressure than for example in the airbox itself. The beauty is that depending on temperature the ambient static pressure will change, directly affecting the reading on the engine, the same applies to altitude. Equally for a MAF sensor the temperature and altitude would also affect the density and hence alter the resistance and thus the signal to the ECU.
A good ram air setup will also add up several percent more static pressure to the engine at high speeds which the above systems would account for. Add to this intake temperature sensors an actual barometric pressure and you have a very complete picture of what is happening with the engine on this topic. Good map sensors have a very small response time of single digit or sub milliseconds even. Therefore transient fueling adjustments can be accounted for which should make a very controllable and thus driveable setup.
With alpha - n you are not measuring a lot of these items, you are trying to predict them indirectly. There will not be an adjustment for ram air and one will be predicting load from the intake temperatures, throttle position and engine rpm, possibly adjusting for barometric pressure. For the tuned conditions there is a good chance this will work absolutely fine. Depending on the tuner they might have to get clever with the transient fueling but you will not have the finesse of an additional load measurement such as the map or maf sensor.
The lambda sensor will give you a reading of oxygen content and therefore the air fuel mixture. Based on the injected fuel this will allow the ecu to calculate the air and thus load on the engine. Depending on the position of the sensor and response time there will typically be some lag.
A MAF or MAP sensor will allow a much more direct measure of load on the engine. On the CSL the MAP sensor should be measuring behind the throttle plates and thus have more variation in static pressure than for example in the airbox itself. The beauty is that depending on temperature the ambient static pressure will change, directly affecting the reading on the engine, the same applies to altitude. Equally for a MAF sensor the temperature and altitude would also affect the density and hence alter the resistance and thus the signal to the ECU.
A good ram air setup will also add up several percent more static pressure to the engine at high speeds which the above systems would account for. Add to this intake temperature sensors an actual barometric pressure and you have a very complete picture of what is happening with the engine on this topic. Good map sensors have a very small response time of single digit or sub milliseconds even. Therefore transient fueling adjustments can be accounted for which should make a very controllable and thus driveable setup.
With alpha - n you are not measuring a lot of these items, you are trying to predict them indirectly. There will not be an adjustment for ram air and one will be predicting load from the intake temperatures, throttle position and engine rpm, possibly adjusting for barometric pressure. For the tuned conditions there is a good chance this will work absolutely fine. Depending on the tuner they might have to get clever with the transient fueling but you will not have the finesse of an additional load measurement such as the map or maf sensor.