Interesting MAF vs. RPM data...
03-05-2007, 05:53 PM
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Interesting MAF vs. RPM data...
<center><img src="http://pictureposter.audiworld.com/87072/aan-maf-data.jpg"></center><p>So turns out MAF output isn't linear in the least. Another interesting point is that the data shows the MAF voltage maxed out as early as 3500 RPMs. How is it that the ECU can properly know how much air is entering the engine if this is the case?
03-05-2007, 06:17 PM
#2
You can't really say whether it's linear from that plot or not...
You can say it's not linear with respect to RPM, but that's not really the issue. For your dual MAF idea you need to know whether the MAF voltage is linear with respect to air mass. I guess in theory given MAP and air temperature at those RPM points and a good estimate of the engine's VE you could approximate the mass flow (a la speed density ECUs) and plot THAT against MAF voltage. That's certainly out of my league though...
How much does a flow bench cost, anyway?
How much does a flow bench cost, anyway?
03-05-2007, 06:48 PM
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Well, the testing was done without a turbo attached, so as a generalization...
the mass of air travelling through the motor and the MAF should double between 2000 and 4000 RPM (correct me if I'm wrong). Instead though, voltage increases from approximately 3.6v to approximately 4.9v.
I wouldn't even want to take a stab at how much a flow bench would cost... lots and lots of Benjamins.
I wouldn't even want to take a stab at how much a flow bench would cost... lots and lots of Benjamins.
03-05-2007, 07:06 PM
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But if Nick could find a CQ body to put his motor/tranny/etc into... that'd be tight.
IMO, and sad to say, but in my case the S4/S6's are too big for a daily driver unless I was frequently hauling people around... but most of the time it's just me in the car and I very rarely have more than one other person in there with me.
03-05-2007, 08:48 PM
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Re: Interesting MAF vs. RPM data...
After a certain point I think the pressure transducer in the ecu takes over. Correct me if i'm wrong. I always thought it would be interesting to remove the cylinder around the hot film/wire in the MAF and replace it with a larger cylinder (like a 4" pvc pipe from Home Depot). You would have to recalibrate the MAF with some sort of signal conditioner to make up for the change. That is the tricky part. This is kinda what Shadetree does with the 928 MAFs (in theory at least). I have some flow maps from a 928 MAF (email me for them). I thought I had one for an RS2 MAF too but I can't seem to find it....
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03-05-2007, 08:52 PM
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^^^Agreed. A few more thoughts...
Okay, first I know I don't belong on this forum (and thus don't have any real credibility), but this info may help.
I agree that RPM is not probably not directly proportional to air flow, but the why would only be speculation on my part.
As far as flow measurement, I can suggest a few things:
1. I know basically every engineering department on my campus has atleast one flow bench. If you have connections with a professor or a graduate student, it might be possible to hook up the MAF to the bench (assuming it doesn't need to be on the car).
2. Buy a hotwire anemometer. See wikipedia link below. These measure MASS airflow very quickly and accurately on the same principle as the MAF in the car, and can be had for a couple hundred bones. Similarly, if you have any connections with anyone who works in a mill or an engineering firm, you could probably borrow one. Another benefit is that this can be done on the car, as the probe is only about .5 cm in diameter.
3. If you have any way of measuring/recording the fuel flow to the injectors and recording the A/F ratio, you could determine the airflow. Plot this vs your MAF data and you're set.
If all this is already obvious to you, i apologize. I'm not sure what you've already considered, but figured I'd do what I could to help. Best of luck!<ul><li><a href="http://en.wikipedia.org/wiki/Anemometer#Hot-wire_anemometers">anemometer</a></li></ul>
I agree that RPM is not probably not directly proportional to air flow, but the why would only be speculation on my part.
As far as flow measurement, I can suggest a few things:
1. I know basically every engineering department on my campus has atleast one flow bench. If you have connections with a professor or a graduate student, it might be possible to hook up the MAF to the bench (assuming it doesn't need to be on the car).
2. Buy a hotwire anemometer. See wikipedia link below. These measure MASS airflow very quickly and accurately on the same principle as the MAF in the car, and can be had for a couple hundred bones. Similarly, if you have any connections with anyone who works in a mill or an engineering firm, you could probably borrow one. Another benefit is that this can be done on the car, as the probe is only about .5 cm in diameter.
3. If you have any way of measuring/recording the fuel flow to the injectors and recording the A/F ratio, you could determine the airflow. Plot this vs your MAF data and you're set.
If all this is already obvious to you, i apologize. I'm not sure what you've already considered, but figured I'd do what I could to help. Best of luck!<ul><li><a href="http://en.wikipedia.org/wiki/Anemometer#Hot-wire_anemometers">anemometer</a></li></ul>
03-05-2007, 09:39 PM
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If you find that RS2 one (RS2 = AAN, only difference is the screens) that would be perfect!
Though having the 928 mapped out would be nice too... I'll shoot you an email mate. Thanks!