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Old 04-19-2015, 08:59 PM   #1
bmwman91
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Random Data Plots - M42 Engine Parameters Stock vs 2.1L Stroker

EDIT: See post #34 for the latest data and findings.

--------------------------------------------------

I finally got my new data logger working and went out to do some quick measurements with it. It is not really intended to be a full engine measurement system, but rather to just measure a few voltage parameters in support of the next-gen MAF conversion I am putting together for the car. Anyway, I figured that I would post up a little bit of information since everyone loves charts and stuff.

First up is a log showing a pull in 2nd gear with the car's current engine (a Metric Mechanic 2.1L M42 with every bell & whistle that MM offers for it along with a couple of extras). Note that the horizontal axis is TIME in milliseconds, not RPM. For the purposes of what I am working on, RPM is not really a factor which is why I am not logging it (I can always add it to the logger in the future). Also note that the green line is AFR which uses the RIGHT vertical axis.


The M42B21 in the above plot is using a 100% stock M42 air box (complete with sort-of-dirty Mahle filter) and VAM. You can see the wild overshoot as I snap onto the throttle and the flapper door bangs open, and then it oscillates a little which causes the AFR to go lean for 100 msec or so. You should also notice that there is not really much of an appreciable lag between when I open the throttle and when the VAM responds, although obviously all accuracy of its output goes straight out the window. I assume that the DME is programmed to account for this though, but I really have no idea there. There also appears to be a fairly significant delay between throttle / VAM signal changes and the AFR responding, maybe indicating that much of the response delay in the system is just due to the DME. Also, the straight horizontal green line is at 14.7 AFR just as a reference for stoichiometric.



Next up is a fun one. I converted the air flow units to CFM since that is probably what folks on here are more familiar with. The orange line is the same one as above (but in CFM instead of CMH). The blue line is from 2007 and the car's original M42B18. Also of note is that the blue line's output came from a MAF sensor, and since I knew the air temperature I could convert the output to CFM from kg/hr. Now, this comparison is subject to whatever inaccuracy is present in both the MAF I used in 2007 and the 20-something year old VAM in my car now. I'd say that the orange VAM signal might be plus/minus 5% accurate and the blue MAF signal is probably pretty dead-on. The logger I built back in 2007 was rudimentary, to put things nicely, compared to what I am using now. Signal accuracy is probably fine though, so this should be a fair-enough comparison.



There are 4 fun things to note here:
1) Cray-cray (that's a technical term, right?) overshoot of the stock VAM when the throttle opens up. The blue line, again, was from a MAF and it keeps its wits about it a lot better since there is no door flapping around all willy-nilly.
2) The peak you see is (I suspect) due to the MM "Pulse Chamber" intake manifold which they say was designed to boost mid-range torque. Clearly it does what it is advertised to, assuming I am guessing right. The green circle for #2 covers ~2000RPM to ~3500RPM, which makes sense given how well this engine behaves at lower RPMs around town. EDIT: This is NOT due to the MM pulse chamber manifold. It is most likely some behavior of the VAM when intake resonances are really bad which make the flapper door open more than it would with steady air flow.
3) The 2.1L engine maxes out the VAM. Output is capped at 240CFM, which is actually in nearly perfect agreement with the Bosch datasheet for the M42's VAM. The first plot shows that the AFR stays good even when the sensor is output is clipped, so the DME doesn't seem to mine the maxed-out VAM since it is working off of custom fuel maps for this engine. I do assume that the VAM is restricting air flow at least little bit in this case though since I am moving enough air through it to peg it at its limit.
4) I "scrunched" the time axis for the blue line for the stock M42. Obviously it took the stock engine longer (about 1 second) to rev all the way up to 7200RPM and I scaled its time axis to align with the MM engine plot for a better comparison.

Another observation is that it is obvious that the stock M42 (blue line) stops breathing as you get into the high-end of the RPM range (it starts flattening at the equivalent of ~5500RPM). The MM M42 looks like it might want to start running of out of breath at the same range, but then it picks back up at ~6000RPM and just keeps going from there. The redline is set at 7700RPM in the DME software, and I can tell you that it pulls nice and hard all the way up to 7700RPM. Apparently I need a bigger air flow meter lol (and I will have a MAF in there soon enough).


I have other plots for idle, part-throttle cruising, stop & go, etc if people are interested. I just thought that this was interesting stuff that I could share from this project.


The logger itself is a side project of mine. It measures each signal 30,000 times a second, hits them with some digital filters, then downsamples to 10,000Hz and sends the data to the PC (so I have 0.1 msec time resolution). There are also some 4th order anti-aliasing filters on each channel to keep RF noise out and that sort of thing. One thing I did find today was that ignition noise is present in all of the analog signals coming from the stock sensors. That is not really much of a surprise, and it isn't a big deal since the DME seems to be fine with working around it. You cannot see it in the plots as they are scaled here, but the idle plot definitely shows "blips" on a very regular period in the VAM, IAT and TPS signals, probably because they are resistive sensors and EMI + high impedance lines means noise spikes.

Funnily enough, my little logger project is more complex than the MAF converter I am now working on. I guess it is like anything...you spend more time prepping and building tools/fixtures than actually doing whatever it is you are doing.
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Old 04-20-2015, 09:08 AM   #2
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Great info dude, love that you keep innovating and pushing forward with the M42 where most of us on here would simply dump the motor for a 24v.
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Old 04-20-2015, 09:13 AM   #3
DER E30
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That's really neat! So are you gonna be selling the MAF conversions?
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Be sure to remind them that the M42 is one of the best engines ever made, but be sure to not mention where it actually falls on that list.
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Old 04-20-2015, 10:04 AM   #4
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Originally Posted by BraveUlysses View Post
Great info dude, love that you keep innovating and pushing forward with the M42 where most of us on here would simply dump the motor for a 24v.
Thanks. Life would be a hell of a lot easier if I stopped wanting to mess with the M42 and just dropped an LS1 or S52 into the car...but, I've owned M42 cars fro 15 years and might as ell keep going lol!

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That's really neat! So are you gonna be selling the MAF conversions?
Funny question. So, the intent all along has been to sell MAF conversions. I even promised to make and sell a kit at least once. Then life got in the way (marriage, blown up M42, bought a house, etc). I would really like to sell a plug-n-play kit though. Once I have my "personal version" up & running, I will see. There is also an audio project that I put together (and posted about extensively on here) and still want to sell, but the head unit it was to go with is no longer available lol...makes it hard to sell the pre-amp boards!
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Old 04-20-2015, 10:07 AM   #5
Dj Buttchug
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wow this is really cool.
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Old 04-21-2015, 10:21 AM   #6
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Huh, that's very interesting. Probably some things to be learned about the volumetric efficiency of an M42 there as well. 17% increase in displacement over stock, but you're seeing a surprisingly consistent 30% improvement in airflow. I'd put a lot of that gains under any porting work that MM does, as well as camshafts, but the nearly constant improvement over the rev range speaks to how well developed their modifications are.
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Old 04-21-2015, 10:42 AM   #7
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Huh, that's very interesting. Probably some things to be learned about the volumetric efficiency of an M42 there as well. 17% increase in displacement over stock, but you're seeing a surprisingly consistent 30% improvement in airflow. I'd put a lot of that gains under any porting work that MM does, as well as camshafts, but the nearly constant improvement over the rev range speaks to how well developed their modifications are.
Yes that is interesting!

Too bad you're not closer, it would be interesting to compare mine to yours! Mine supposedly has a ported/flowed head with s14 profile cams.
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Be sure to remind them that the M42 is one of the best engines ever made, but be sure to not mention where it actually falls on that list.
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Old 04-21-2015, 12:04 PM   #8
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Yeah, the aross-the-board 30-40% increase in air flow is a little surprising since displacement is only up 17%. Maybe 5-10% of it could be due to accuracy variance between the two different air flow sensors. But then again, the MM figure of 205bhp vs ~150bhp stock+chip is ~37% higher, which obviously means a lot more air getting in there. One of the big things with MM when I spoke with them was their emphasis on building a well-balanced engine that still retains a broad, useful powerband. Anyone can build a top-end screamer, but I think that their careful work on the head and cam profiles are a big part of why this thing sees gains across the entire RPM range, while still pulling hard all the way to 7700RPM. All I can say is that this engine wants to be driven hard...it takes a lot of restraint to not floor it every chance I get lol.
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Old 05-08-2015, 07:54 AM   #9
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interesting ... !!!
any information more detail for MAF conversion?

thank you
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Old 05-08-2015, 08:21 AM   #10
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Cool!

No matter what system you use, the AFR's will spike when stabbing the throttle.

Interesting to see the AFM is maxed out. Not surprising, though, when you increased the displacement by 20% or so.

I have found that the BMW's likes to run about 13.5:1 when in accelerator enrichment (WOT), most engines seem to like high 12's better. Stoich is more for idle, lean cruise will be in the 16's or so.

It would be interesting to add a tach input to log so you aren't judging by ms.
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Old 05-08-2015, 09:26 AM   #11
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I love data, thanks for sharing
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Old 06-13-2015, 06:33 PM   #12
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A couple of updates...

1) I installed my MAF conversion and it is up and running. This is the 7th iteration of the device (a project which I began in 2005 lol). This time around, it looks like I finally put all of my mad nerd skillz to work in the right way and it's a solid device.

2) I have added a 5th analog channel to the data logger, as well as RPM input. Within a couple of weeks I should have the VR sensor conditioner board and be able to get even more detailed logs for everyone's enjoyment.
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Old 06-13-2015, 09:03 PM   #13
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Nice! Eager to see the results!
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Be sure to remind them that the M42 is one of the best engines ever made, but be sure to not mention where it actually falls on that list.
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Old 06-14-2015, 01:41 PM   #14
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Originally Posted by bmwman91 View Post
A couple of updates...

1) I installed my MAF conversion and it is up and running. This is the 7th iteration of the device (a project which I began in 2005 lol). This time around, it looks like I finally put all of my mad nerd skillz to work in the right way and it's a solid device.

2) I have added a 5th analog channel to the data logger, as well as RPM input. Within a couple of weeks I should have the VR sensor conditioner board and be able to get even more detailed logs for everyone's enjoyment.
Is this something you ever think you will manufacture to sell? Could use if I ever decided to go FI.
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Old 06-14-2015, 02:25 PM   #15
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Is this something you ever think you will manufacture to sell? Could use if I ever decided to go FI.
+1 really interested to see if this makes any power NA as well.
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