So much forum confusion about alpha-n tunes vs csl tunes

[Sajk]

Alpha-n is a crippled limp home tune the dme contains to get you home safe in the event of maf failure. From the factory it is a safe tune that will work anywhere on the planet without destroying the engine due to detonation. It is not an upgrade from maf based tuning its a downgrade. Csl tuning uses a map or manifold absolute pressure sensor to drive what is called speed density tuning which is the dominant tuning scheme used by several vendors most noticeably by nu,ber of units is Chrysler.

This is not alpha-n. Alpha-n can be made to work for one set of fuel / temp / altitude conditions, drive from 6000 feet above sea level to the coast. Oops. Lean or rich or something.

Why is it viewed as a holy grail of performance tunes?

[TomK]

Csl tuning uses a map or manifold absolute pressure sensor to drive what is called speed density tuning which is the dominant tuning scheme used by several vendors most noticeably by nu,ber of units is Chrysler.

From one of the most well regarded tuners in the UK..
"CSLs also run Alpha-N, not speed-density (MAP). The MAP sensor is there for EOBD compliance because the load system has to have a redundancy function. That's why CSLs have higher resolution in the Alpha-N maps because without the MAF it's the primary load measure, not the backup. Vacuum signal is too poor and fluctuates too much to use MAP with any degree of precision."

Why is it viewed as a holy grail of performance tunes?

Where do you see that? Most of the time all I see is alpha-n being rubbished.

[Sajk]

I will take your word for it. Manifold Absolute Pressure sensors are used so that the DME can guess at the airflow. All Chrysler engines except a few use this system. They call it speed density and I know a little about the software having tuned a few. I think it's mostly semantics. Chrysler speed density system uses the map pressure to index into pre set tables to establish fueling etc. I would think thus is exactly what the csl tune is doing they just call it alpha n.

I read about lots of people doing alpha n conversions with no map. This is a crippled tune and at best works OK for the set of environmental conditions in place when it was flashed.

[TomK]

Well I don't see anyone forcing you to get one, so you should be fine?

A CSL airbox added to an S54 is arguably one of the best engine sounds available. With our MSS70 ecu there is no possibility of adding a MAP sensor but for the reasons I noted above it's really not necessary, if I need to run "Alpha-N" to achieve that sound then so be it. I've had no issues with the tune/driveability/engine in 7 years, certainly no regrets!! The MSS70 has the advantage of even better resolution than the MSS54HP the CSL used, I'd hope Martyn on here can chime in as he probably knows the MSS70 better than almost anyone...

[Martyn]

I don't think anyone is claiming it a holy grail, it's a means to end allowing the use of CSL style intakes, nothing more, nothing less.

The MSS70 found in the Z4M runs dual widebands in full time closed loop and is significantly more advanced than the MSS54/MSS54HP found in the E46 M3 and M3 CSL, the MSS70 also has an inbuilt baro sensor so is able to compensate for elevation changes with or without the MAF.

[Ed Doe]

Alpha-n is simply a mathematical function, where alpha is a variable (throttle plate position) and N is a number, which in this situation is rpm - hence its a formula for working out the volumetric efficency % of the engine at a given rpm and throttle position. This information is then used by the ecu to workout which ignition and fuel tables to read from, giving you your fuel and spark advance.

Using map sensor simply measures the manifold pressure for a given rpm to calculate volumetric efficiency.

There's more to it (such as the need for iat sensors and barometric sensors to further define the spark and fuelling tables for specific temperature and pressure combinations) to calculate mass airflow but ultimately its slightly different ways to achieve the same same thing - the clever bit surely lies in the ability of a mapper to do a decent job of the map...

Feel free to correct me if I'm wrong, the above is my understanding, but I'll be the first hold my hand up and say I'm no mapper!

[Sajk]

Well I bow to greater knowledge . Alot of my reading has been on e46 m3 which as far as I know does not possess widebands or built in map sensors. I read about a lot of people installing carbon air boxes for the sound who may or may not be on an alpha n piston melting party with a canned tune as without factory widebands or widebands when dialing in said tune their is no real way for the dme to know. Maybe a trim maxed out code. Anyway.. .

[Martyn]

The MSS54/MSS54HP has a built in baro sensor too FYI.

The ECU will throw a code if the fuel trims are maxed out, alphaN or not, besides, it's easy to max those trims out when you have an intake leak post MAF sensor but how many cars do you see with melted pistons? The MSS54 might well run narrowband O2s but it still knows what is rich, and what is lean both in the short and long term via its trims.

I've tuned loads of E46 M3 track and race cars and have never seen melted pistons from 'just' running AlphaN, but then I dial things in with an external wideband during setup. Things tend to 'blow up' or melt stuff when knock factors are heavy massaged and overly agressive ignition timing is added.

This aside, cars with ITBs tend to create very little vacuum at low and medium loads, and therefore arent really very well suited to using MAP as a primary load source, hence why TPS or MAF is a better load source for the S54.

[Justino]

The MSS54/MSS54HP has a built in baro sensor too FYI

Didn't know that.

My conclusion is that given the MAP on the E46 CSL is there probably just as a backup, and that vacuum is not that a reliable source in any event, that a Z4M with Alpha N, given the barometric adjustment in built into the ECU, the greater processing over a CSL ECU 'might' actually be better than a CSL setup, certainly no worse ?

[Sajk]

Found this on m3 cutters. This is how I also understand it.

See below snippet from M3Carbon1’s page.

“
Now onto the mapping aspect. There are a couple of options available:

1. Alpha N mapping

2 CSL ECU conversion mapping

Alpha N is basically a way of the engine calculating how much load is on the engine using RPM and Throttle position. This information is sent to the ecu via these sensors and then into a table where a load is calculated, Alpha N can work well, but it can be a little lumpy on part throttle acceleration, but top end is responsive, this has been a comment from many using this setup, but after some time, you can adapt to the car and find your way around it. Peak output power is around 350-355bhp. (standard car healthy engine 330bhp on a well setup dyno dynamics) the standard BMW software is modified for more power and MAF sensor deletion. Because the Alpha N setup does not have an actual way of measuring since the MAF has been removed, it is guessing the load, and is less accurate and that shows slightly while driving, but it still does a pretty good job and fine for most.

CSL ECU Conversion - This is where the entire platform of the software is changed. There are 2 types of ECU that are in the E46 M3, the MSS54 (2001- October 2002) Then the MSS54HP, which is the newest version coming in at around September 2002 - 2005, with bigger storage capacity, and a few small changes. Essentially the HP unit is the same as a stock CSL ECU without the associated hardware to run the flap which the stock csl has, just to clear up questions regarding the flap, there is no real need to fit, it has no difference in terms of performance and was mainly implemented to speed up air speed into the engine but mainly sound restriction at low rpm, (who would want that!).

A solution is available that if you have the earlier ecu, it can be modified to accept the full CSL conversion, the later ecu needs no hardware modifications and can be flashed directly with CSL software. The MSS54 unit is upgraded by changing the EEPROMS that store the software, and some resistors, when this has been carried out, the unit is then technically a HP unit ready to accept CSL software, which is uploaded to the ecu via BDM, a method which is known for programming the EEPROMS directly thought a programmer connected to the ECU.

The best option here is the CSL ecu conversion, it has a completely different calibration compared to Alpha N and is more complex, one of the reasons that this is the better option is because the CSL software runs with a map sensor, the map sensor uses a vacuum reading in order to calculate load and is accurate. This basically is replacing the MAF and has a 3rd load reference, Alpha N has 2, this results in a smoother and more responsive throttle and gives you the 'cable' feel of the throttle and not fly by wire, which the M3 uses, which makes it feel far more responsive and smoother

[Sajk]

And this

Right, just come across this and time to put this to bed. Whilst Alpha N doesn't solely work on throttle position and RPM, its significantly flawed and I will tell you why, there is no *true* load reference, which is exactly what a MAP sensor/MAF sensor does. Putting it simply, having a map sensor helps with tip in throttle slightly, dont get me wrong though, it isnt a massive difference but just keeps everything running cleaner, I would rather have it than not having it, an extra point of reference is always a good thing.

The CSL software can run well without the map sensor, just better with. With a stock modified software which has been changed to support an airbox, doesnt run very well, it wasnt designed for it, as the CSL software was hence the mapping being far more advanced to what we know as 'Alpha N'. The map sensor isnt ignored, its used as a reference for air density which will then adjust fueling as needed, especially at tip in throttle, Who said it wasnt needed?

Alpha N will make good top end power, but part throttle drivability and response isnt great at all, lumpy and jerky, but Haider by the sounds if it you have a CSL software installed anyway.

Based on the fact that the CSL Conversion software is actual software that came off of the CSL and is designed to run a gearbox, its 100% worth it. There are many calibrations added within that software that many do not know about in comparison to modified normal software to work with an airbox, it just isnt logical.

Its an amazing mod and well worth the money, over the years and as per my tutorials and every single cutters members cars I have worked on, there have literally been smiles from ear to ear, which keeps me doing this. For what its worth, a decat with this mod works really well too.

Regarding the video above, the owner of this car had a high attention to detail and high expectation and he was very happy.

Mike

[Martyn]

None of that has anything to do with the MSS70?

[TomK]

See below snippet from M3Carbon1’s page.

That guys tuning reputation is poor, I wouldn't listen to a word of it.

What is the point of this thread exactly? If you don't have an e46 with a CSL airbox why are you thinking about alpha-n tunes and whether they are better/worse/same as CSL and discussing it here?

[Slideways]

OP, I recommend reading the tech docs that BMW made for the CSL and the E9X M3. They describe how the engine management works in both cars. Martyn did a very good job explaining it though.

[Sajk]

"I recommend reading the tech docs that BMW made for the CSL and the E9X M3. They describe how the engine management works in both cars. Martyn did a very good job explaining it though."

That would be great. Love to. Do you have a link.