Calculating VE from a MAF sensor

[whipped]

Okay, MAF sensor tells us airflow in grams/sec. Given you know the temp of the air, and relative humidity to calculate the density... And can log it according to MAP and RPM, wouldn't it be pretty easy to put out a pretty accurate VE table? I mean, it wouldn't even depend on the AFR or AE or PE or any of that stuff, since for one RPM and manifold pressure, there's only one VE... you know?

In addition to that....... Is VE not directly proportional to torque? Do I hear a poor man's dyno being constructed in my mind? :scratch:

[eHoward]

I think we talk about that in the turbo thread.

off the forum, we've been doing power estimates for GM engines based on dyno runs and turbo plots from other manufacturers.

Okay, MAF sensor tells us airflow in grams/sec. Given you know the temp of the air, and relative humidity to calculate the density... And can log it according to MAP and RPM, wouldn't it be pretty easy to put out a pretty accurate VE table? I mean, it wouldn't even depend on the AFR or AE or PE or any of that stuff, since for one RPM and manifold pressure, there's only one VE... you know?

In addition to that....... Is VE not directly proportional to torque? Do I hear a poor man's dyno being constructed in my mind? :scratch:

[whipped]

off the forum, we've been doing power estimates for GM engines based on dyno runs and turbo plots from other manufacturers.

What? (confused about what you're talking about) :scratch:

Anybody know the output of standard MAF sensors? Would like a nice linear 0-5 volt output... My wideband can log that.

Northstar? Ls1? L98?

Nice. http://www.dainst.com/info/maf/ford_mustang_maf.html

hmm... I think the northstar is like 1400kg/hr though.. Using the 50lb/min figure

[The Dark Side of Will]

GM MAF's output frequency proportional to flow.

However, you'd have to tune with a MAF computer and then use the MAF tables so derived to calculate your VE table... not really practical.

MAF tables in MAF computer = VE tables in MAP computer

The table equates frequency to airflow... The sensor is supposed to have a certain curve, but lots of things can affect that like the nature of ductwork around the sensor, distance from throttle body, etc.

[eHoward]

Forgive me, I'm tired.

For the poor man's dyno, i was talking about using the theoretical CFM to estimate torque.

What? (confused about what you're talking about) :scratch:

[whipped]

GM MAF's output frequency proportional to flow.

However, you'd have to tune with a MAF computer and then use the MAF tables so derived to calculate your VE table... not really practical.

MAF tables in MAF computer = VE tables in MAP computer

The table equates frequency to airflow... The sensor is supposed to have a certain curve, but lots of things can affect that like the nature of ductwork around the sensor, distance from throttle body, etc.

all GMs, or just late models? Are the L98's frequency output?

If you look at the link above, the mustang sensor has a table for flow and output voltage. My wideband can record RPM, MAP, and the output from a 0-5 volt MAF at the same time... Seems like that's all I'd need to put together a VE table. Granted, it won't be 100% accurate, like you said due to differences in calibration vs actual, but it would give the proper shape, which in tuning, is all you need. Then you can just shift the whole table up and down to lock it in.

In addition, if you have the shape, and an actual dyno run to back it up, you can just sync the two. Voila, you can dyno every mod after that for free.

Just thinking outside the box...

[Sinister Fiero]

all GMs, or just late models? Are the L98's frequency output?

The L98's (Bosch) were a 0-5v analog voltage output. All others were frequency based.

If you look at the link above, the mustang sensor has a table for flow and output voltage. My wideband can record RPM, MAP, and the output from a 0-5 volt MAF at the same time... Seems like that's all I'd need to put together a VE table. Granted, it won't be 100% accurate, like you said due to differences in calibration vs actual, but it would give the proper shape, which in tuning, is all you need. Then you can just shift the whole table up and down to lock it in.

To properly calculate airflow, you need to use absolute manifold pressure and temperature along with maps of other engine variables such as volumetric efficiency. Obviously it is going to be easy to figure out MAP and MAT, but actual VE is going to be the difficult one to nail down.

[whipped]

all GMs, or just late models? Are the L98's frequency output?

The L98's (Bosch) were a 0-5v analog voltage output. All others were frequency based.

To properly calculate airflow, you need to use absolute manifold pressure and temperature along with maps of other engine variables such as volumetric efficiency. Obviously it is going to be easy to figure out MAP and MAT, but actual VE is going to be the difficult one to nail down.

I thought they would be... They run on the 7730, which probably wouldn't have the power to be monitoring both rpm and MAF... I don't understand your next paragraph though...

The MAF tells us airflow in grams/sec. Of course, we need to bring that to a standard temp and pressure, but you can get that from the BARO reading and MAT sensor... Then VE is just actual airflow divided by calculated airflow... right? Stuff those values into a table of RPM vs MAP, and you've got a ve table.

[The Dark Side of Will]

all GMs, or just late models? Are the L98's frequency output?

The L98's (Bosch) were a 0-5v analog voltage output. All others were frequency based.

To properly calculate airflow, you need to use absolute manifold pressure and temperature along with maps of other engine variables such as volumetric efficiency. Obviously it is going to be easy to figure out MAP and MAT, but actual VE is going to be the difficult one to nail down.

I thought they would be... They run on the 7730, which probably wouldn't have the power to be monitoring both rpm and MAF... I don't understand your next paragraph though...

The MAF tells us airflow in grams/sec. Of course, we need to bring that to a standard temp and pressure, but you can get that from the BARO reading and MAT sensor... Then VE is just actual airflow divided by calculated airflow... right? Stuff those values into a table of RPM vs MAP, and you've got a ve table.

What do you mean both run 7730? The L98 MAF engines used the '165.

Theoretically, what you say about VE is so, but you hinge a lot on the MAF calibration.

[whipped]

What do you mean both run 7730? The L98 MAF engines used the '165.

Theoretically, what you say about VE is so, but you hinge a lot on the MAF calibration.

err... sorry. you're right.

Like I said before, MAF calibration is irrelevant. Even if it's off 10%, you can take that into account.

For instance, in the cheap homemade dyno, you just take it to a real dyno, and you have several points you can "calibrate" it to.

In the tuning/VE table example, you have the shape of the curve down, you just shift it up and down with the BPW constant until it locks in.

[The Dark Side of Will]

The calibration may not be off by a consistent amount due to resonances and intake tract turbulence that change with different engien airflow demands. This is why MAF based engine management still needs to be tuned.

[whipped]

merde.

[whipped]

here's an interesting post from DIY-EFI:

Here is part of a post from Feb 02, this year:

========================================================================
Here's a formula that should work:

VE = m_dot / ( N * Vol * Rho / 120 ) * 100

where: VE - volumetric efficiency (%)
m_dot - mass air flow (g/s)
N - crank speed (rpm)
Vol - Engine Displacement (litres)
Rho - Manifold Air Density (g/litre)

where: Rho = 1.202 * MAP / 101.325
MAP = Manifold Absolute Pressure (kPa)

You should also compensate the air density for temperature too since
the 1.202 is air density at 20_C and inlet temperature is elevated due
to heat transfer from the manifold surfaces etc.

Also VE for family cars these days will probably be better than 80%.
======================================================================

That was posted by Andrew Rabbitt from Orbital, a while ago.
Much simpler, and the variables are available in the ECM. I worked
on this off and on for a while because I could not get a good
match with the table VE and MAF VE. It takes a fair amount of
effort to get it to work right.

Where are you getting "T" (air temp) in your setup? How accurate
do you think it is? After taking 9 months or so to get the
variables right, my MAF VE and table VE usually match quite well
over the whole operating temp range. And it is not over 80% VE,
in my case. Much closer to 65% max at 100 kPa MAP

I make the ECM calculate VE real time, then save it in added
non-vol RAM. It took a while, but the results are very
gratifying now....

Scot Sealander