Please Read --> MAF Sensors with the EMS - Great Thread!

[andris]

I understand the way each type of system works, but there are still some inaccuracies floating around.  There are several types of MAF sensors out there that have been used in recent years.  Karmann vortex (DSM), flapper/plunger (older mazdas, others), thin-film (Subaru, can't remember the proper name), and Hotwire (many modern cars, including ford, mazda, nissan, toyota).  The flapper and karmann sensors seem to typically use baro and or temp sensors to get a usable reading.  I don't know enough about the film sensors to talk about how they work.  I know a good bit about hotwire sensors because I have built a few cars that use them.  I'll use my personal car as an example.. It is an early-90's Nissan Sentra that runs a hotwire MAF sensor stock.  It does not have a Baro or temp sensor anywhere on the car stock.  The TPS is mainly used just as a switch to tell the computer when to go out of closed-loop.  It also has some minor functions on throttle tip-in at low rpms because of the lag between throttle opening and MAF reading.  However, the car will run nearly perfect with the TPS unplugged; free-revving, driving around, no problem.   The car is turbocharged and the stock computer has been reprogrammed to run a 300zx twin-turbo MAF sensor, which is accurate to around 450+ hp.  It is ~3" I.D. with a small bridge across the middle to hold the wire, but not really what I would call a significant intake restriction.  With a bone-stock motor (normally aspirated) I've plugged in the 300zx maf, computer, and 72lb injectors and the car drove as if it were completely stock.  Bolt on the turbo stuff and run 15psi and the tuning is still dead-on.   I really don't understand why people don't like them.  Maybe they're thinking about flapper-door sensors when they think "intake restriction" ?  As i stated earlier, altitude (density) has no effect on mass, so the comments about needing a baro sensor for that are incorrect.  (still talking about hotwire sensors here).  

andris

[anoldsman]

Andris wrote:

As i stated earlier, altitude (density) has no effect on mass, so the comments about needing a baro sensor for that are incorrect. (still talking about hotwire sensors here).

I think that you have the basics correct but your assumptions are incorrect.  You are correct that the mass of air will not change after the air goes through the turbo or after it has been measured.  But, you MUST know the baro pressure and air temperature to determine air mass flow rate.  The equation is ma = Va * ρ where ma is mass flow rate, Va is volumetric flow rate and ρ is air density.  
A hot-wire MAF heats up a wire to a constant temperature above ambient.  This combined with the baro pressure allows the MAF to measure the mass flow rate.  If the MAF does not look at intake air temp then it will not work properly since it can not hold a constant temperature difference across the hot-wire.  
A 2.7 change in mercury (pressure) has the same affect as changing the air temp by 47 degrees.  While most of us will not see this much of a range it shows how baro must be used to correctly measure mass air flow.

But, I do agree with you 100% that a MAF is more accurate and when correctly matched to the engine will not be a restriction.  Hopefully I will be able to test an edge orifice MAF or a GM MAF against a the MAP to tell you of the differences.  But money does not fall from trees.   So, it will be a while.  

Chris

[andris]

Look, baro and temp are NOT NEEDED if you are truly measuring mass.  Maybe KV sensors need them because the vortex measurement does not 100% represent mass.  Maybe flapper meters need them because they only measure velocity or something.  This is not something I can tell you for sure; I can tell you with certainty that most hotwire MAF sensors DO accurately measure mass without the aid of temperature or pressure sensors.  

You completely contradict yourself with the formula you used.  You have mass on one side and volume and density on the other.  This shows that a measurement of mass is representative of both volume and density.  This is BASIC PHYSICS.   Take for example a solid chunk of steel with a mass of 1 kilogram.   Got it?  Now go drive it up to the top of Mt Everest and weigh it.. What do you get? 1 kilo.   Death valley? one kilo.  500 degrees in an oven? 1 kilo.  Antarctica? 1 kilo.  in the rain? one kilo. See where I'm going with this?  Mass is constant regardless of the other factors.  One sticking point I think we are having is that maybe some types of FLOW meters people are thinking of are not really measuring MASS.  If you have a true measurement of mass, things like altitude, pressure and temperature DO NOT MATTER.  

andris

[SA]

I agree with Andris.  The Karman Vortex sensor measures air flow VELOCITY...not MASS AIR FLOW.  To get a variable proportional to mass air flow, you need an indication of temperature and pressure as well.

A hot wire/film mass air flow sensor provides a voltage output that is proportional to MASS AIR FLOW.  No temperature or pressure compensations are necessary.

I don't know about the GM sensor.  From what I've read here, it outputs a frequency that is proportional to MASS AIR FLOW.

SA

[BLKMGK]

Okay, I guess I see where I'm getting confused - I've not ever worked with any MAF other than the Fords. It sounds as if there are MAFs that operate on principles that I'm ignorant of. I can live with that

Honestly, if the actual airflow can be measured, not inferred, without restriction then an argument could certainly be made that that this is a better way to measure load.

Imagine not having to deal with IAT correction tables Would the fuel map be a straight VE table at that point?

[chevyeater]

This is the GM 3 1/2" MAF I would like to use on my car. It outputs a square wave frequency variable from approximately 0Hz to 39KHz that is directly proportional to mass air flow. It needs ignition power feed, ground and a regulated 5 volts on the sensor circuit. Would this work in KV mode on the EMS with the baro and air temp corrections turned off?

[SA]

I'm pretty sure it would.  You might have to play with the scaling to get the range you need but it should be do-able.  You won't be able to log your load in units of mass airflow though...like you can with the 0-5V MAF sensors.  Just run the output into the EMS Spare Speed Input (T4) then configure it just like any DSM KV sensor.

SA

[andris]

I don't know about all Ford MAF sensors used in recent years (and how they measure), but another data point:  Besides the 300zxTT MAF, the other very common MAF sensor to swap into Sentras and 240sx is a mid-90's Mustang Cobra MAF (with an appropriate calibration/program)  It is a hotwire just like the various nissan units.  I think they are all made by hitachi.  0-5v.  That is on cars with no temp or baro sensors.

Regarding the GM maf - If it is not feasible to use it as-is, you could make a simple frequency>voltage converter that outputs 0-5v and run it like any other sensor.  

The Infiniti Q45 MAF outputs 0-5v and (IIRC) can read accurately into the 6-700 hp range.

andris

[chevyeater]

Kewl.  

[BLKMGK]

Hrm, I have a 42lb calibrated Ford bullet MAF sort of laying around. Wonder if it might be worthwhile to play with on a spare input. If nothing I'd like to know if it presents any sort of restriction. Unfortunatly I've not got the calibration sheet for it any longer but it was made to work in place of a stock Ford MAF....

[andris]

This may be an ignorant question, but why would it matter what the calibration curve looks like?  0 volts is nothing, and 5 volts is all it will read.  You're going to be tuning from scratch anyways, so the MAF provides the Y-axis and you'll just be tuning it to whatever it needs to be in each cell.  I can imagine that some sort of calibration or reference point is needed for a frequency MAF, but 0-5 volts is 0-5 volts.   I suppose that knowing what voltage=what airflow might be helpful for picking breakpoints.. Like if nothing really happened from 0-1v, you wouldn't need a bunch of cells in that area.  

If you hooked up the MAF you've got laying around and just datalogged what it reads, you'd be way ahead of the game if you ever wanted to actually use it because you'd already have an idea how much fuel is needed for what MAF reading.  

andris

[BLKMGK]

Well... it came with one when new so I figure they must have had SOME reason for including it. I also recall looking at one and noting that the response curve was NOT linear. It just seems to me that in order to best use something like this you would want to know what X voltage equals so far as airflow. I guess I have some fantasy idea that if you knew how much air was bieng moved at X RPM you could come up with effeciency figures and maybe even take a shot at building a fuel map prior to ever firing it up.

I watched a guy reflash an EECV Mustang not long ago and it was kind of interesting to watch as his biggest concern was simply how much air was being moved (duh). Not so cool was finding out just how many MAFs he had seen maxed out on high powered combinations! Overall it looked somewhat easy in that his main concerns were adding X amount of fuel with Y amount of air to get a specific A/F. Timing appeared to be the primary tuning point, I think the other stuff was pretty straightforward. He used lots of Excel spreadhseets to do calcs and conversions.

My turn for a stupid question - which type of MAF are the Ford units Pro-M makes? My MAF equipped Ford had both IAT and Baro sensors. Given a choice I'd prefer NOT having to worry about those corrections. Which MAF exactly can do this that flows oh say 750+HP worth of air? The MAF I have I think would choke things but I might be able to get a bigger Ford MAF easily enough

P.S. Having to recirculate my BOV would SUCK though. Bleah!

[andris]

A lot of the reason guys like the mustang dudes worry about calibrations is that they aren't doing any real tuning - just substituting matched parts (like 43lb injectors and a MAF machined to read the right thing) and going on their merry way.  Tuning from scratch it probably matters less.

RE: sensors.. Just because MAF sensors can measure mass doesn't mean manufacturers don't have baro or temp sensors on the car.  I know that the second generation of Nissan SE-Rs added a temp sensor in the airbox, but the MAF functionality remained unchanged.  The sensor was there for cranking/startup or something smog-related (I can't remember).  I'm sure there are similar cases with other manufacturers.

From what I gathered from the pro-flow.com site, they are hotwire sensors.  A quick look at their site shows meters good for 800+ hp.  If you want to get tricky you can also divide the flow.  This makes most sense on twin turbo cars, but anyways... Jim Wolf Technology has a program for running two cone filters on a 300zx instead of one.  The MAF measures one side and a dummy MAF (piece of tubing or something) resides in the other one.  Now you are flowing twice the air with the same sensor reading.  This setup is widely used on high hp 300xzs and performs flawlessly.   You'd just need to make sure both tubes had the same bends/length.

andris

[a10ha10ha7]

so are you guys saying that the STOCK MAF sensor on the MKIV supra can be used with the AEM EMS. but now how are we suppose to get the cailbration for it? anyone have a techtom? lets plug it in to the Stock EUC and find the calibration for the MAF on the SUPRA.

the stock MKIV supra has the AIT on the MAF and has a MAP. so why does it need all these sensors, when its got a MAF that does'nt need Baro and temp? what was the stock ECU doing with the Baro and Temp sensors?

oh ya one question to Andris, does the MAF mesures the vol of Air by the hotwired and it does not need a baro or temp becuase when Altiude goes up air gets thiner therfore there is less air cooling the hotwire but if there were more velocity it will make up for the thiner pressure density, therefore making the MAF with hotwire type dont need the Baro and temp sensor?

i m not trying to question anyone but i m trying to learn more.

and i want to put the MAF back into my Supra, i m looking for only 600hp is there any japanese MAF out there that can take 600Hp perhaps DENSO?
or is there any japanese MAF that can take 600HP

thanks for helping out
and i'v learned alot with the post of this topic
 

[SA]

I made this thread a sticky and modified the title a little.  There's been a lot of confusion lately regarding this subject.  IMO this thread has some great discussion!

SA