Random Data Plots - M42 Engine Parameters Stock vs 2.1L Stroker

[bmwman91]

Dredging this up from the depths again...

I have been doing a lot of research into the stock ECU's map programming and stuff, as well as talking to SSSQuid about doing some live dyno tuning in December. For the time being, I figured enough things out to modify my WOT fuel maps and deal with the 2500-3500RPM leaning issue. Sure, enough, the maps all had a lean region in that RPM range, and I am convinced that it is precisely because the stock VAM over-reports air flow in that range at WOT thanks to intake resonance.

Here are some AFR comparisons from 2nd gear WOT pulls. The first 2 (green and blue) are with the base tune for my built engine. The second two (orange and yellow) are from today with the first round of mods I made to my WOT fuel tables. Not only are the numbers more sensible, but it has a lot more power in that RPM range. I did also make some small changes to the fueling near max 6000 to enrich things a little there too, although it doesn't look like it did all that much. It could be because my original pulls were done in the middle of summer, and today the temperature was a lot lower and the humidity a lot higher. Who knows.



Also, here is a little plot showing what all I did to the WOT fuel map. The values are converted to AFR's for ease of viewing (instead of the raw hex values from the BIN dump).




So, in a month or two I expect to have a FULL custom tune done on a dyno. This excites me, because the car is fun as hell now, and I think that there may be a fair bit of optimization in the fuel and spark tables that has yet to be done. I will definitely post up the dyno results when those are in! This also puts some stuff to bed regarding the MAF conversion...to actually have it run right, you either need a modified WOT fuel table, or a MAF converter that also takes in RPM and throttle position so as to mimic the stock sensor's non-linearities.

[bmwman91]

They are not the exact injectors that were used for the original tune (the chip was developed for the MM 2.1L engine design, not custom burned for this specific engine). I guess that there was some sort of issue with the 24# EV6 injectors that were originally selected (pintles getting stuck open) so MM had me order some 24# EV1 ones. There is more to an injector than the static flow rate, but it's what the option was at the time. The chip was not re-tuned for the different 24# injectors.

I don't have the exact specs for the centerlines. But, based on the timing map for the grind and assuming that the lobes are symmetric about the centerline, the intake CL is 117deg ATDC and the exhaust centerline is 120deg BTDC. The combined cam CL is then 152deg BTDC (92deg separation between intake and exhaust CL's).

If someone local could tune Motronic 1.7, I would have gotten on a dyno and had a custom tune made LONG ago. Sadly, nobody in the region works with it and going stand-alone isn't something I have time for now (or in the foreseeable future).

[digger]

Not sure why the LTFT indicates that the time-zero fueling is way too rich. This engine does have 24# injectors (vs stock 21#) and a custom chip. MM worked with MarkD on the software, so I would imagine that the fuel tables are at least halfway decent.

The cams are 272deg intake and 258deg exhaust (0.125mm lift). Peak lift is 11.40mm intake and 11.15mm exhaust.

are those the injectors that MarkD recommends with that chip?

what centrelines are the cams installed on?

[bmwman91]

Not sure why the LTFT indicates that the time-zero fueling is way too rich. This engine does have 24# injectors (vs stock 21#) and a custom chip. MM worked with MarkD on the software, so I would imagine that the fuel tables are at least halfway decent.

The cams are 272deg intake and 258deg exhaust (0.125mm lift). Peak lift is 11.40mm intake and 11.15mm exhaust.

[digger]

S
So, I think that the AFR's look fairly good, except in the 2500 - 3500 RPM range. The LTFT leans things out even more in that range. I am amazed that I don't have issues with knock since the engine has 11.5:1 compression and we only get 91 octane around here. It must be somewhat of a testament to Metric Mechanic's head and piston developments.

why does the LTFT have such quick and large effect? are you using much larger injectors than are actually needed?

what cam centrelines and duration are being used?

[bmwman91]

Yeah, SMOG regulations in my state make things a little more of a pain, especially NOx when it comes to ignition timing tweaks. It also means that the engine has to look mostly stock (since I want to avoid having to swap manifolds for the test every 2 years!).

Anyway, I'll see if I can get MarkD to tweak the WOT fuel table in the 2500-3500RPM range to enrich things a little. The maps were purposely leaned out there because the stock AFM has a resonance there and over-reports air flow in that range with large throttle openings (whereas my MAF does not do this and remains accurate).

[digger]

about 5% in various chunks of the powerband IIRC, i dont have good records from back then since is was 2006/07. with SMOG and all that shit it probably makes it a little harder perhaps

[bmwman91]

I am planning to go with MS3Pro eventually. That is a big long-term project and I am planning to do it in a plug-n-play style with the factory harness, plus a few improvements (sequential injection, MAF support, maybe ignition coils with integrated drivers). In the meantime, I want to get this thing dialed in more properly and enjoy it before ripping things apart again!

How much power did you gain with a custom tune versus the stock one provided by MM/MarkD?

[digger]

why not a MS or other aftermarket system? it make s a big difference to be able run the fuel and timing the engine needs as compared to generic maps. The MarkD chip for my MM was not even close to being optimal

[bmwman91]

Slight resurrection...

I did a little more data logging today now that I am 100% certain that the long term fuel trim (LTFT) is fully in place. Here is a comparison between 2 of the runs I did today, and a couple from a year ago shortly after I reset the ECU.



What's what?
MAF 1 and MAF 2 lines are from today's WOT pulls in 2nd gear, and I last reset the ECU ~4 months ago during an audio project.
MAF 3 is a 2nd gear WOT pull from about 5 minutes after resetting the ECU.
MAF 4 is a 2nd gear WOT pull from about 10 minutes after resetting the ECU.

So, I think that the AFR's look fairly good, except in the 2500 - 3500 RPM range. The LTFT leans things out even more in that range. I am amazed that I don't have issues with knock since the engine has 11.5:1 compression and we only get 91 octane around here. It must be somewhat of a testament to Metric Mechanic's head and piston developments.

Anyway, I am going to try to work with MarkD to get a customized map that enriches things in that range a little so that I don't get that dead spot in the powerband anymore. What are everyone's thoughts on the rest of the AFR's throughout the powerband?

[varg]

The main point is that getting power from the NA M42 is expensive.

Fixed ;)

This thread delivers. Lots of neat info.

[bmwman91]

I can tell your an engineer, I love reading your findings. Thanks for your contribution.

Off topic, if you had to do it all over again, would you go MM? Considering costs vs. gains.
My engine is getting up there in miles and I'm expecting any day to have to make a choice, rebuild to stock or upgrade.

Thanks for the kind words.

Would I go with MM again? Hard to say. On the one hand, their customer service is excellent, they are fanatics about what they do and they deliver a quality product. On the other hand, they are $$$ and a built M42 from them will take as long as building one yourself with a competent local shop (I initially figured that MM would be faster, but they don't get many M42 orders so everything had to be special ordered for the build). I'd say that if there is a highly competent builder local to you and you don't depend on the car as a DD, then you might save a few $thousand that way. MM has extensive experience with BMW head work and they developed their own cam profiles, so I think that they might have an advantage over an engine shop that does not specialize in BMW, particularly older ones.

Either way, parts will cost you an arm and a leg. The M47 crank is like $1300 these days (new), and I bet that parts alone for a 2.1L high compression build will cost at least $4000. The machine labor will probably be another $2000-3000. So, you could save a couple $thousand by assembling most or all of it yourself. You would also want to look into using the M44 timing case with its larger oil pump and more reliable design, although you would need a crank position sensor bracket.

The main point is that getting power from the M42 is expensive.

[eur04lif3]

I can tell your an engineer, I love reading your findings. Thanks for your contribution.

Off topic, if you had to do it all over again, would you go MM? Considering costs vs. gains.
My engine is getting up there in miles and I'm expecting any day to have to make a choice, rebuild to stock or upgrade.

[bmwman91]

So, I revisited the data that I took this summer and put together another plot. This time I displayed the air flow rates and AFR's from all 4 runs, with RPM as the X-axis. The most obvious thing is that the first run from each sensor is MUCH richer than the second run. Remember that I unplugged/reset the Motronic before swapping sensors, so it was re-learning all of the short- and long-term fuel trim settings. There was ~5 minutes of run-time after reconnecting the Motronic and doing the first pull, and then another 5 minutes after that until the second pull. Since the second pull is leaner, a big factor must be in allowing the Motronic to adjust based on run-time data from the O2 sensor.

OK. Here's the plan. I reinstalled the datalogger hardware this evening. I am to put at least 100 miles on this thing so that the Motronic will (hopefully) be fully adjusted, and then I will log some more 2nd gear pulls with the MAF (which is on there now). I will probably also log the idle and some part-throttle driving just for the sake of completeness. Thereafter, the VAM will get stuffed back in, the Motronic reset and after 100+ miles I will do the same measurements with it. Does anyone here know how many hours of operation it generally takes for the Motronic to establish its long-term fuel trim values?

Here is the plot of data that I mentioned at the start of this post.


The green and orange lines are the first runs after resetting the Motronic with the engine at full operating temperature (green is MAF, orange is VAM). Similarly, the blue and yellow lines are the second runs, at which point the Motornic has had 10-15 minutes of operation at full operating temperature (blue is MAF, yellow is VAM).

You will notice that the first runs are much richer than the second ones. My main interest here is the blue and yellow lines below 3500RPM. On these second runs, the MAF runs a lot leaner than the VAM (AFR of 15.0 vs 13.5). This corresponds exactly to the big "bump" in air flow signal coming from the VAM in that range. Someone correct me if I am wrong, but an AFR of 15.0 at WOT is not a recipe for power, and I think that this must be why I "feel the bog" in that range.

I have no reason to believe that the VAM+stock air box is magically flowing that much more air in that range, and as noted in a prior post, I think that it is a resonance effect interacting with the VAM's door which causes an artificially high output voltage from the VAM sensor, which just about any M42 tune will have factored in. Since the MAF accurately reports air flow here, it ends up passing through the tuning tables and leads to leaner running since the table tuned with the assumption that air flow is over-reported in this range. I do seem to recall hearing unverified information over the years that indicates that the Motronic runs off of the 2D maps below 4000RPM regardless of throttle position, which means that it is using the air flow voltage as a primary load signal, and then above 4000RPM if the throttle is open more than 80% it switches to 1D maps for faster response (in which case the air flow signal is largely ignored). From looking at how well the AFR's match above 4000RPM, this seems like it could be the case.

The initial implications here are that there may very well be no way that the M42 can ever have a "perfect" plug-and-play MAF conversion. You would either need a chip with a tune that is not based on a big bump in voltage from 2500-3500RPM, or you would need a MAF converter that taps into the crank position sensor and throttle potentiometer...in which case it really can't be called plug-and-play anymore since you are cutting wires. Maybe I could work an FFT algorithm in to the converter that basically allows the RPM to be read from the pulse frequency of the raw MAF signal, and then a correction curve is applied which mimics the VAM's goofy signal bump from 2500-3500RPM.

Phew. That is a lot of text. At this point, I know one thing for certain. It is time to find a tuner that can work with M1.7 and get a custom tune for this engine with the MAF installed.



For a little bit of extra fun, this link has a ~11,000 pixel wide plot. This one has the raw MAF output signal on it, and it is super duper wide which allows you to see how ugly the signal is. Every single intake valve opening is clearly visible! Remember, in this plot the horizontal axis is in milliseconds, not RPM.

http://www.e30tuner.com/assist/b21secondgear_superwideintakepulses.png

[digger]

What's cams do mm use in these things? Did they give a full camcard ?