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Old 07-19-2012, 01:20 AM   #41
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I'm so sick of arguing with you, but I can't let myself leave misinformation in an otherwise very helpful thread full of correct design and theory.

A calibration curve is just that, a sensor calibration, in our case a MAF. The calibration curve is not going to change no matter where that sensor is, given a few constants. Here, I'm going to assume temperature and pressure are constant across all scenarios. Did you catch that assumption? (I know you missed the one where I assumed his calibration curve was accurate) The mass of air moving through the sensor correlated to a voltage output from the sensor (actually a resistance change across the sensor body) is not going to change whether that same MAF is on a laboratory bench, in a miata, a corvette, or on an airplane. It doesn't matter whether the air goes through ten miles of pipe first or nothing at all. The sensor will still output a given voltage for a given amount of air flow. I'm assuming this calibration is known. I know how to measure and generate my own calibration for whatever MAF, but I haven't done enough research to know whether a GM MAF calibration equation is accurate for a miata MAF or not. So, if you know that calibration, and can plot the raw voltage reading, you will know with some degree of accuracy how much air goes through the motor. From there, calculating the VE is simply a math problem. Are you all caught up now?
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Old 07-19-2012, 01:25 AM   #42
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Originally Posted by baron340 View Post
I'm so sick of arguing with you, but I can't let myself leave misinformation in an otherwise very helpful thread full of correct design and theory.

A calibration curve is just that, a sensor calibration, in our case a MAF. The calibration curve is not going to change no matter where that sensor is, given a few constants. Here, I'm going to assume temperature and pressure are constant across all scenarios. Did you catch that assumption? (I know you missed the one where I assumed his calibration curve was accurate) The mass of air moving through the sensor correlated to a voltage output from the sensor (actually a resistance change across the sensor body) is not going to change whether that same MAF is on a laboratory bench, in a miata, a corvette, or on an airplane. It doesn't matter whether the air goes through ten miles of pipe first or nothing at all. The sensor will still output a given voltage for a given amount of air flow. I'm assuming this calibration is known. I know how to measure and generate my own calibration for whatever MAF, but I haven't done enough research to know whether a GM MAF calibration equation is accurate for a miata MAF or not. So, if you know that calibration, and can plot the raw voltage reading, you will know with some degree of accuracy how much air goes through the motor. From there, calculating the VE is simply a math problem. Are you all caught up now?
Thank you!
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Old 07-19-2012, 01:41 AM   #43
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it will change, but it depends on the piping, size of the inlets, bends, etc
size of the maf housing.

been there and dealt with it.
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Old 07-19-2012, 05:06 AM   #44
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it will change, but it depends on the piping, size of the inlets, bends, etc
size of the maf housing.

been there and dealt with it.
No. It will not change. Practically the first rule of fluid dynamics: what is flowing through a pipe at one point must be flowing through it at all points.

I'm done reading you. I wish there was a way to block your posts.

You don't learn, you don't want to learn.
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Old 07-19-2012, 07:00 AM   #45
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Quote:
Originally Posted by baron340 View Post
I'm so sick of arguing with you, but I can't let myself leave misinformation in an otherwise very helpful thread full of correct design and theory.

A calibration curve is just that, a sensor calibration, in our case a MAF. The calibration curve is not going to change no matter where that sensor is, given a few constants. Here, I'm going to assume temperature and pressure are constant across all scenarios. Did you catch that assumption? (I know you missed the one where I assumed his calibration curve was accurate) The mass of air moving through the sensor correlated to a voltage output from the sensor (actually a resistance change across the sensor body) is not going to change whether that same MAF is on a laboratory bench, in a miata, a corvette, or on an airplane. It doesn't matter whether the air goes through ten miles of pipe first or nothing at all. The sensor will still output a given voltage for a given amount of air flow. I'm assuming this calibration is known. I know how to measure and generate my own calibration for whatever MAF, but I haven't done enough research to know whether a GM MAF calibration equation is accurate for a miata MAF or not. So, if you know that calibration, and can plot the raw voltage reading, you will know with some degree of accuracy how much air goes through the motor. From there, calculating the VE is simply a math problem. Are you all caught up now?
Yes. But I dont plan on using the GM math, because well, the maf is very different internally from that. Ours is quite strange looking inside actually, bad enough that if I cant find the formula I'm completely unwilling to derive it myself. And all the GM cars I have access to have the maf built into the air box so I couldnt even borrow a GM maf.
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Old 07-19-2012, 11:03 AM   #46
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No. It will not change. Practically the first rule of fluid dynamics: what is flowing through a pipe at one point must be flowing through it at all points.

I'm done reading you. I wish there was a way to block your posts.

You don't learn, you don't want to learn.
the point of screens in front of and behind the maf housing is to keep flow laminar. Well if you put say a bend infront of the maf it can easily move the majority of the mass flow away from the middle of sensor as it flows past. Anyone with tuning experince deadling with maf tuning will know this. They will also know by changing out to a bigger housing a maf sensor can be made to read higher airflow. The best way to know what its output to airflow is in a setup is to actually use it for fuel control. Get it down so you know what the airflow numbers are. And yes it does matter if the maf has straight piping before vs no piping before the maf. It will affect sensor readings.

Last edited by Techsalvager; 07-19-2012 at 01:35 PM.
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Old 07-19-2012, 02:05 PM   #47
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Tech is correct. The Maf is calibrated for the tube dia it is mounted within. It only samples a small fraction of the airflow so the cal is velocity sensitive. If you use the same dia as what the Maf originally used, and can ensure laminar flow (straight sections up and downstream of the Maf) then the original cal curve will remain valid. Use a larger dia and you will need to recharacterize the Maf if you want an accurate cal curve.
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Old 07-19-2012, 06:46 PM   #48
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Tech is correct. The Maf is calibrated for the tube dia it is mounted within. It only samples a small fraction of the airflow so the cal is velocity sensitive. If you use the same dia as what the Maf originally used, and can ensure laminar flow (straight sections up and downstream of the Maf) then the original cal curve will remain valid. Use a larger dia and you will need to recharacterize the Maf if you want an accurate cal curve.
Yes... ...obviously.

The MAF as a sensor works within the parameters of a given tube, and if you deliberately set out to sabotage the flow through that tube, you could affect the calibration.

But if you use it as intended, it doesn't matter what else that MAF/tube combination is connected to. It measures the flow through the tube and the flow through the rest of the system MUST be the same.
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Old 07-20-2012, 10:01 AM   #49
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Originally Posted by alangbaker View Post
Yes... ...obviously.

The MAF as a sensor works within the parameters of a given tube, and if you deliberately set out to sabotage the flow through that tube, you could affect the calibration.

But if you use it as intended, it doesn't matter what else that MAF/tube combination is connected to. It measures the flow through the tube and the flow through the rest of the system MUST be the same.
And how you gonna use as intended on a completely different car\engine with different size piping? And yes it always matters what maf\tube combination it is if its anything different then a stock it will change.
actual flow though the tube maybe the same but airflow vs output has changed

where with a bend infront it maybe 1v at idle
and without a bend infront it maybe .7v at idle.

Last edited by Techsalvager; 07-20-2012 at 10:14 AM.
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Old 07-20-2012, 02:03 PM   #50
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Originally Posted by Techsalvager View Post
And how you gonna use as intended on a completely different car\engine with different size piping? And yes it always matters what maf\tube combination it is if its anything different then a stock it will change.
actual flow though the tube maybe the same but airflow vs output has changed

where with a bend infront it maybe 1v at idle
and without a bend infront it maybe .7v at idle.
It only matters if the flow is change so that a significantly different fraction flows past the wire, and that is not nearly as easy as you imagine. Could one do it deliberately? Probably. Is it going to happen because you have a different bend in the pipe flowing into it? Almost certainly not.

Go away.
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Old 07-20-2012, 05:35 PM   #51
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It only matters if the flow is change so that a significantly different fraction flows past the wire, and that is not nearly as easy as you imagine.

Go away.
Not as easy as I imagine?
Do you have first hand experince tuning maf based systems?

Quote:
Could one do it deliberately? Probably. Is it going to happen because you have a different bend in the pipe flowing into it? Almost certainly not.
lol
Yes it will happen.
It happens so easily as well
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Old 07-20-2012, 06:49 PM   #52
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Not as easy as I imagine?
Do you have first hand experince tuning maf based systems?
I have schooling and personal study in fluid dynamics. Keeping a fluid from adopting a flow pattern where the pressures vary significantly inside a tube is no simple matter.


Quote:
lol
Yes it will happen.
It happens so easily as well
Prove it.
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Old 07-23-2012, 06:00 PM   #53
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Sure probably over the weekend I will look at doing it again
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Old 07-23-2012, 06:15 PM   #54
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I'll cross post this, because I at the very least seriously doubt the VE numbers in the actual tune on a hydra, VE number and HP numbers really arent correlating to something that makes sense. This person does not want me discussing the tune, but I will say based on the VE numbers in that tune and the HP its making stock 1.8 would be in the low 70's for peak VE if the numbers in the hydra are to be believed. So rather than basing it off the fuel table we will just have to do the math ourselves. https://dl.dropbox.com/u/18163809/Ho...ityWorks16.doc
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Old 07-23-2012, 06:21 PM   #55
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I know nothing about Hydra, but VE is rarely really VE. For example in MS1, it is not at all. In MS2 B&G, it's not either. In MS2Extra it CAN be, but ONLY if you enable a non-default option, and have multiply MAP turned on (this shouldn't even BE an option). Even then, I'd be weary of the numbers as you'd need to set up ReqFuel perfectly and that's rarely done correctly, if ever. In fact, it's often beneficial to not do it "correctly". Thus, with a closed source EMS like Hydra, your only option is to do the math yourself.
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Old 07-23-2012, 06:58 PM   #56
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I'm used to mostly dealing with GM car, and GM has their own VE which does things a bit different, so seeing a tune that hits 198% VE is nothing abnormal to me. But the work I've done with haltech suggests that at least they use real VE and the numbers seem to make sense. But I guess everything just has to be different.
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Old 07-23-2012, 07:06 PM   #57
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OK, that's good to know about Haltech. FreeEMS does it "right" too, fwiw.
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Old 08-09-2012, 10:41 AM   #58
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Hey leafy, are you suggesting that the actual VE for the 1.8 motor is closer to 70%? Sorry, I have had a lot of family issues lately (deaths in the family) and haven't been on to keep track of everyones posts on my thread :P
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Old 08-09-2012, 10:43 AM   #59
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No, just saying that based off the last hydra tune I did that would likely be the result in another hydra tune with the same injectors and comp tables (likely stock comp tables, owner specifically wanted me to not touch them). 70% is unrealistically low for real VE.
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Old 08-09-2012, 10:45 AM   #60
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Would you say my assumed 80% is too low as well? Have you noticed an increase in VE across the RPM range at all? Specifically a linear increase?
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